I didn’t think this was going to be so troublesome! but wanted to note down the steps to resolve.<\/p>\n\n\n\n
The ‘Build Virtual Raster<\/strong>‘ process in QGIS will not bring together multiple rasters if they span across 2 CRS projections Following my initial post of the issue on GIS stackexchange:https:\/\/gis.stackexchange.com\/questions\/342830\/cant-join-multiple-dems-using-qgis-build-virtual-raster-if-they-span-2-crss<\/a> A users tip re unifying the projections for loaded data sent me in the right direction.<\/p>\n\n\n\n\n\n\n\nAdding test selection of DEM’s from the following ALOS PALSAR<\/strong> dataset into QGIS:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAs you can see we have only 1 DEM tile on 20S <\/strong>CRS, so we\u2019ll see if we can simply re-project that one to match the others with 21S<\/strong><\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nFirst switch QGIS project CRS to 21S<\/strong> (bottom right globe icon)<\/p>\n\n\n\nCreate shapefile for square extent in this case 250000 x 250000:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nExtent: (229085.941613, 4146747.332439) – (479085.941613, 4396747.332439)<\/p>\n\n\n\nRun the Warp<\/strong> process on the single 20S <\/strong>DEM tile:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nOr if you need to carry out the warp process on multiple dem files, just use the ‘Run as Batch Process<\/strong>‘ button bottom left of screen shot above. And select all the assets you want re-projected:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAnd fill out the appropriate fields:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nOr you could use Python to carry out the same GDAL task:<\/p>\n\n\n\nimport os\npath=r\"F:\/GIS\/Falklands\/dem\/\"\nfor file in os.listdir(path):\n if file.endswith(\".tif\"):\n print path+\"\/\"+file\n os.system('\"gdalwarp.exe\"'\/\n +' -dstnodata -multi -s_srs EPSG:32720 '\/\n +'-t_srs EPSG:32721 -r cubic '+path+\"\/\"+file\/\n +' F:\/GIS\/Falklands\/dem\/'+file+' -wo NUM_THREADS=8')<\/code><\/pre>\n\n\n\nLayers over perfectly:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nNow run Build virtual Raster <\/strong>selecting only the assets that are EPSG:32721<\/strong><\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nFor some reason QGIS can’t render this new vrt<\/strong> very well:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nBut we will push\nforward and use the gdalwarp<\/strong> command to\ncut the new virtual raster above to the square extent created earlier:<\/p>\n\n\n\nNot forgetting to switch the CRS <\/strong>to 32721<\/strong> which is what the virtual raster is set to:<\/p>\n\n\n\ngdalwarp -t_srs EPSG:32721 -wo SOURCE_EXTRA=1000 -tr 12.5 12.5 -srcnodata \"-9999\" -r cubic -ot Float32 -of GTiff -te 229085.941613 4146747.332439 479085.941613 4396747.332439 \"F:\/GIS\/Falklands\/virtual_final.vrt\" F:\/GIS\/Falklands\/dem_final.tif<\/code><\/pre>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAll working nicely on UTM 21S<\/strong> CRS:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nI’m not too happy having to process a DEM up to three times to get to a clean unified extract of the full dataset, so I’ll keep looking for an alternative, potentially doing it all via GDAL commands. But degradation of the data seems to be kept to a minimum, likley helped by using cubic convolution resampling.<\/p>\n","protected":false},"excerpt":{"rendered":"I didn’t think this was going to be so troublesome! but wanted to note down the steps to resolve. The ‘Build Virtual Raster‘ process in QGIS will not bring together multiple rasters if they span across 2 CRS projections Following my initial post of the issue on GIS stackexchange:https:\/\/gis.stackexchange.com\/questions\/342830\/cant-join-multiple-dems-using-qgis-build-virtual-raster-if-they-span-2-crss A users tip re unifying the … Read More<\/a><\/span><\/p>\n","protected":false},"author":1,"featured_media":1203,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2,4],"tags":[],"_links":{"self":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160"}],"collection":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=1160"}],"version-history":[{"count":22,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions"}],"predecessor-version":[{"id":1216,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions\/1216"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media\/1203"}],"wp:attachment":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=1160"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=1160"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=1160"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
Adding test selection of DEM’s from the following ALOS PALSAR<\/strong> dataset into QGIS:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAs you can see we have only 1 DEM tile on 20S <\/strong>CRS, so we\u2019ll see if we can simply re-project that one to match the others with 21S<\/strong><\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nFirst switch QGIS project CRS to 21S<\/strong> (bottom right globe icon)<\/p>\n\n\n\nCreate shapefile for square extent in this case 250000 x 250000:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nExtent: (229085.941613, 4146747.332439) – (479085.941613, 4396747.332439)<\/p>\n\n\n\nRun the Warp<\/strong> process on the single 20S <\/strong>DEM tile:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nOr if you need to carry out the warp process on multiple dem files, just use the ‘Run as Batch Process<\/strong>‘ button bottom left of screen shot above. And select all the assets you want re-projected:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAnd fill out the appropriate fields:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nOr you could use Python to carry out the same GDAL task:<\/p>\n\n\n\nimport os\npath=r\"F:\/GIS\/Falklands\/dem\/\"\nfor file in os.listdir(path):\n if file.endswith(\".tif\"):\n print path+\"\/\"+file\n os.system('\"gdalwarp.exe\"'\/\n +' -dstnodata -multi -s_srs EPSG:32720 '\/\n +'-t_srs EPSG:32721 -r cubic '+path+\"\/\"+file\/\n +' F:\/GIS\/Falklands\/dem\/'+file+' -wo NUM_THREADS=8')<\/code><\/pre>\n\n\n\nLayers over perfectly:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nNow run Build virtual Raster <\/strong>selecting only the assets that are EPSG:32721<\/strong><\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nFor some reason QGIS can’t render this new vrt<\/strong> very well:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nBut we will push\nforward and use the gdalwarp<\/strong> command to\ncut the new virtual raster above to the square extent created earlier:<\/p>\n\n\n\nNot forgetting to switch the CRS <\/strong>to 32721<\/strong> which is what the virtual raster is set to:<\/p>\n\n\n\ngdalwarp -t_srs EPSG:32721 -wo SOURCE_EXTRA=1000 -tr 12.5 12.5 -srcnodata \"-9999\" -r cubic -ot Float32 -of GTiff -te 229085.941613 4146747.332439 479085.941613 4396747.332439 \"F:\/GIS\/Falklands\/virtual_final.vrt\" F:\/GIS\/Falklands\/dem_final.tif<\/code><\/pre>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAll working nicely on UTM 21S<\/strong> CRS:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nI’m not too happy having to process a DEM up to three times to get to a clean unified extract of the full dataset, so I’ll keep looking for an alternative, potentially doing it all via GDAL commands. But degradation of the data seems to be kept to a minimum, likley helped by using cubic convolution resampling.<\/p>\n","protected":false},"excerpt":{"rendered":"I didn’t think this was going to be so troublesome! but wanted to note down the steps to resolve. The ‘Build Virtual Raster‘ process in QGIS will not bring together multiple rasters if they span across 2 CRS projections Following my initial post of the issue on GIS stackexchange:https:\/\/gis.stackexchange.com\/questions\/342830\/cant-join-multiple-dems-using-qgis-build-virtual-raster-if-they-span-2-crss A users tip re unifying the … Read More<\/a><\/span><\/p>\n","protected":false},"author":1,"featured_media":1203,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2,4],"tags":[],"_links":{"self":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160"}],"collection":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=1160"}],"version-history":[{"count":22,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions"}],"predecessor-version":[{"id":1216,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions\/1216"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media\/1203"}],"wp:attachment":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=1160"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=1160"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=1160"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
As you can see we have only 1 DEM tile on 20S <\/strong>CRS, so we\u2019ll see if we can simply re-project that one to match the others with 21S<\/strong><\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nFirst switch QGIS project CRS to 21S<\/strong> (bottom right globe icon)<\/p>\n\n\n\nCreate shapefile for square extent in this case 250000 x 250000:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nExtent: (229085.941613, 4146747.332439) – (479085.941613, 4396747.332439)<\/p>\n\n\n\nRun the Warp<\/strong> process on the single 20S <\/strong>DEM tile:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nOr if you need to carry out the warp process on multiple dem files, just use the ‘Run as Batch Process<\/strong>‘ button bottom left of screen shot above. And select all the assets you want re-projected:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAnd fill out the appropriate fields:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nOr you could use Python to carry out the same GDAL task:<\/p>\n\n\n\nimport os\npath=r\"F:\/GIS\/Falklands\/dem\/\"\nfor file in os.listdir(path):\n if file.endswith(\".tif\"):\n print path+\"\/\"+file\n os.system('\"gdalwarp.exe\"'\/\n +' -dstnodata -multi -s_srs EPSG:32720 '\/\n +'-t_srs EPSG:32721 -r cubic '+path+\"\/\"+file\/\n +' F:\/GIS\/Falklands\/dem\/'+file+' -wo NUM_THREADS=8')<\/code><\/pre>\n\n\n\nLayers over perfectly:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nNow run Build virtual Raster <\/strong>selecting only the assets that are EPSG:32721<\/strong><\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nFor some reason QGIS can’t render this new vrt<\/strong> very well:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nBut we will push\nforward and use the gdalwarp<\/strong> command to\ncut the new virtual raster above to the square extent created earlier:<\/p>\n\n\n\nNot forgetting to switch the CRS <\/strong>to 32721<\/strong> which is what the virtual raster is set to:<\/p>\n\n\n\ngdalwarp -t_srs EPSG:32721 -wo SOURCE_EXTRA=1000 -tr 12.5 12.5 -srcnodata \"-9999\" -r cubic -ot Float32 -of GTiff -te 229085.941613 4146747.332439 479085.941613 4396747.332439 \"F:\/GIS\/Falklands\/virtual_final.vrt\" F:\/GIS\/Falklands\/dem_final.tif<\/code><\/pre>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAll working nicely on UTM 21S<\/strong> CRS:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nI’m not too happy having to process a DEM up to three times to get to a clean unified extract of the full dataset, so I’ll keep looking for an alternative, potentially doing it all via GDAL commands. But degradation of the data seems to be kept to a minimum, likley helped by using cubic convolution resampling.<\/p>\n","protected":false},"excerpt":{"rendered":"I didn’t think this was going to be so troublesome! but wanted to note down the steps to resolve. The ‘Build Virtual Raster‘ process in QGIS will not bring together multiple rasters if they span across 2 CRS projections Following my initial post of the issue on GIS stackexchange:https:\/\/gis.stackexchange.com\/questions\/342830\/cant-join-multiple-dems-using-qgis-build-virtual-raster-if-they-span-2-crss A users tip re unifying the … Read More<\/a><\/span><\/p>\n","protected":false},"author":1,"featured_media":1203,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2,4],"tags":[],"_links":{"self":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160"}],"collection":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=1160"}],"version-history":[{"count":22,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions"}],"predecessor-version":[{"id":1216,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions\/1216"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media\/1203"}],"wp:attachment":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=1160"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=1160"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=1160"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
First switch QGIS project CRS to 21S<\/strong> (bottom right globe icon)<\/p>\n\n\n\nCreate shapefile for square extent in this case 250000 x 250000:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nExtent: (229085.941613, 4146747.332439) – (479085.941613, 4396747.332439)<\/p>\n\n\n\nRun the Warp<\/strong> process on the single 20S <\/strong>DEM tile:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nOr if you need to carry out the warp process on multiple dem files, just use the ‘Run as Batch Process<\/strong>‘ button bottom left of screen shot above. And select all the assets you want re-projected:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAnd fill out the appropriate fields:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nOr you could use Python to carry out the same GDAL task:<\/p>\n\n\n\nimport os\npath=r\"F:\/GIS\/Falklands\/dem\/\"\nfor file in os.listdir(path):\n if file.endswith(\".tif\"):\n print path+\"\/\"+file\n os.system('\"gdalwarp.exe\"'\/\n +' -dstnodata -multi -s_srs EPSG:32720 '\/\n +'-t_srs EPSG:32721 -r cubic '+path+\"\/\"+file\/\n +' F:\/GIS\/Falklands\/dem\/'+file+' -wo NUM_THREADS=8')<\/code><\/pre>\n\n\n\nLayers over perfectly:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nNow run Build virtual Raster <\/strong>selecting only the assets that are EPSG:32721<\/strong><\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nFor some reason QGIS can’t render this new vrt<\/strong> very well:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nBut we will push\nforward and use the gdalwarp<\/strong> command to\ncut the new virtual raster above to the square extent created earlier:<\/p>\n\n\n\nNot forgetting to switch the CRS <\/strong>to 32721<\/strong> which is what the virtual raster is set to:<\/p>\n\n\n\ngdalwarp -t_srs EPSG:32721 -wo SOURCE_EXTRA=1000 -tr 12.5 12.5 -srcnodata \"-9999\" -r cubic -ot Float32 -of GTiff -te 229085.941613 4146747.332439 479085.941613 4396747.332439 \"F:\/GIS\/Falklands\/virtual_final.vrt\" F:\/GIS\/Falklands\/dem_final.tif<\/code><\/pre>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAll working nicely on UTM 21S<\/strong> CRS:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nI’m not too happy having to process a DEM up to three times to get to a clean unified extract of the full dataset, so I’ll keep looking for an alternative, potentially doing it all via GDAL commands. But degradation of the data seems to be kept to a minimum, likley helped by using cubic convolution resampling.<\/p>\n","protected":false},"excerpt":{"rendered":"I didn’t think this was going to be so troublesome! but wanted to note down the steps to resolve. The ‘Build Virtual Raster‘ process in QGIS will not bring together multiple rasters if they span across 2 CRS projections Following my initial post of the issue on GIS stackexchange:https:\/\/gis.stackexchange.com\/questions\/342830\/cant-join-multiple-dems-using-qgis-build-virtual-raster-if-they-span-2-crss A users tip re unifying the … Read More<\/a><\/span><\/p>\n","protected":false},"author":1,"featured_media":1203,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2,4],"tags":[],"_links":{"self":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160"}],"collection":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=1160"}],"version-history":[{"count":22,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions"}],"predecessor-version":[{"id":1216,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions\/1216"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media\/1203"}],"wp:attachment":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=1160"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=1160"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=1160"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
Create shapefile for square extent in this case 250000 x 250000:<\/p>\n\n\n\n
Extent: (229085.941613, 4146747.332439) – (479085.941613, 4396747.332439)<\/p>\n\n\n\n
Run the Warp<\/strong> process on the single 20S <\/strong>DEM tile:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nOr if you need to carry out the warp process on multiple dem files, just use the ‘Run as Batch Process<\/strong>‘ button bottom left of screen shot above. And select all the assets you want re-projected:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAnd fill out the appropriate fields:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nOr you could use Python to carry out the same GDAL task:<\/p>\n\n\n\nimport os\npath=r\"F:\/GIS\/Falklands\/dem\/\"\nfor file in os.listdir(path):\n if file.endswith(\".tif\"):\n print path+\"\/\"+file\n os.system('\"gdalwarp.exe\"'\/\n +' -dstnodata -multi -s_srs EPSG:32720 '\/\n +'-t_srs EPSG:32721 -r cubic '+path+\"\/\"+file\/\n +' F:\/GIS\/Falklands\/dem\/'+file+' -wo NUM_THREADS=8')<\/code><\/pre>\n\n\n\nLayers over perfectly:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nNow run Build virtual Raster <\/strong>selecting only the assets that are EPSG:32721<\/strong><\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nFor some reason QGIS can’t render this new vrt<\/strong> very well:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nBut we will push\nforward and use the gdalwarp<\/strong> command to\ncut the new virtual raster above to the square extent created earlier:<\/p>\n\n\n\nNot forgetting to switch the CRS <\/strong>to 32721<\/strong> which is what the virtual raster is set to:<\/p>\n\n\n\ngdalwarp -t_srs EPSG:32721 -wo SOURCE_EXTRA=1000 -tr 12.5 12.5 -srcnodata \"-9999\" -r cubic -ot Float32 -of GTiff -te 229085.941613 4146747.332439 479085.941613 4396747.332439 \"F:\/GIS\/Falklands\/virtual_final.vrt\" F:\/GIS\/Falklands\/dem_final.tif<\/code><\/pre>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAll working nicely on UTM 21S<\/strong> CRS:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nI’m not too happy having to process a DEM up to three times to get to a clean unified extract of the full dataset, so I’ll keep looking for an alternative, potentially doing it all via GDAL commands. But degradation of the data seems to be kept to a minimum, likley helped by using cubic convolution resampling.<\/p>\n","protected":false},"excerpt":{"rendered":"I didn’t think this was going to be so troublesome! but wanted to note down the steps to resolve. The ‘Build Virtual Raster‘ process in QGIS will not bring together multiple rasters if they span across 2 CRS projections Following my initial post of the issue on GIS stackexchange:https:\/\/gis.stackexchange.com\/questions\/342830\/cant-join-multiple-dems-using-qgis-build-virtual-raster-if-they-span-2-crss A users tip re unifying the … Read More<\/a><\/span><\/p>\n","protected":false},"author":1,"featured_media":1203,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2,4],"tags":[],"_links":{"self":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160"}],"collection":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=1160"}],"version-history":[{"count":22,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions"}],"predecessor-version":[{"id":1216,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions\/1216"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media\/1203"}],"wp:attachment":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=1160"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=1160"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=1160"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
Or if you need to carry out the warp process on multiple dem files, just use the ‘Run as Batch Process<\/strong>‘ button bottom left of screen shot above. And select all the assets you want re-projected:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAnd fill out the appropriate fields:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nOr you could use Python to carry out the same GDAL task:<\/p>\n\n\n\nimport os\npath=r\"F:\/GIS\/Falklands\/dem\/\"\nfor file in os.listdir(path):\n if file.endswith(\".tif\"):\n print path+\"\/\"+file\n os.system('\"gdalwarp.exe\"'\/\n +' -dstnodata -multi -s_srs EPSG:32720 '\/\n +'-t_srs EPSG:32721 -r cubic '+path+\"\/\"+file\/\n +' F:\/GIS\/Falklands\/dem\/'+file+' -wo NUM_THREADS=8')<\/code><\/pre>\n\n\n\nLayers over perfectly:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nNow run Build virtual Raster <\/strong>selecting only the assets that are EPSG:32721<\/strong><\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nFor some reason QGIS can’t render this new vrt<\/strong> very well:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nBut we will push\nforward and use the gdalwarp<\/strong> command to\ncut the new virtual raster above to the square extent created earlier:<\/p>\n\n\n\nNot forgetting to switch the CRS <\/strong>to 32721<\/strong> which is what the virtual raster is set to:<\/p>\n\n\n\ngdalwarp -t_srs EPSG:32721 -wo SOURCE_EXTRA=1000 -tr 12.5 12.5 -srcnodata \"-9999\" -r cubic -ot Float32 -of GTiff -te 229085.941613 4146747.332439 479085.941613 4396747.332439 \"F:\/GIS\/Falklands\/virtual_final.vrt\" F:\/GIS\/Falklands\/dem_final.tif<\/code><\/pre>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAll working nicely on UTM 21S<\/strong> CRS:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nI’m not too happy having to process a DEM up to three times to get to a clean unified extract of the full dataset, so I’ll keep looking for an alternative, potentially doing it all via GDAL commands. But degradation of the data seems to be kept to a minimum, likley helped by using cubic convolution resampling.<\/p>\n","protected":false},"excerpt":{"rendered":"I didn’t think this was going to be so troublesome! but wanted to note down the steps to resolve. The ‘Build Virtual Raster‘ process in QGIS will not bring together multiple rasters if they span across 2 CRS projections Following my initial post of the issue on GIS stackexchange:https:\/\/gis.stackexchange.com\/questions\/342830\/cant-join-multiple-dems-using-qgis-build-virtual-raster-if-they-span-2-crss A users tip re unifying the … Read More<\/a><\/span><\/p>\n","protected":false},"author":1,"featured_media":1203,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2,4],"tags":[],"_links":{"self":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160"}],"collection":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=1160"}],"version-history":[{"count":22,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions"}],"predecessor-version":[{"id":1216,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions\/1216"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media\/1203"}],"wp:attachment":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=1160"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=1160"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=1160"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
And fill out the appropriate fields:<\/p>\n\n\n\n
Or you could use Python to carry out the same GDAL task:<\/p>\n\n\n\n
import os\npath=r\"F:\/GIS\/Falklands\/dem\/\"\nfor file in os.listdir(path):\n if file.endswith(\".tif\"):\n print path+\"\/\"+file\n os.system('\"gdalwarp.exe\"'\/\n +' -dstnodata -multi -s_srs EPSG:32720 '\/\n +'-t_srs EPSG:32721 -r cubic '+path+\"\/\"+file\/\n +' F:\/GIS\/Falklands\/dem\/'+file+' -wo NUM_THREADS=8')<\/code><\/pre>\n\n\n\nLayers over perfectly:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nNow run Build virtual Raster <\/strong>selecting only the assets that are EPSG:32721<\/strong><\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nFor some reason QGIS can’t render this new vrt<\/strong> very well:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nBut we will push\nforward and use the gdalwarp<\/strong> command to\ncut the new virtual raster above to the square extent created earlier:<\/p>\n\n\n\nNot forgetting to switch the CRS <\/strong>to 32721<\/strong> which is what the virtual raster is set to:<\/p>\n\n\n\ngdalwarp -t_srs EPSG:32721 -wo SOURCE_EXTRA=1000 -tr 12.5 12.5 -srcnodata \"-9999\" -r cubic -ot Float32 -of GTiff -te 229085.941613 4146747.332439 479085.941613 4396747.332439 \"F:\/GIS\/Falklands\/virtual_final.vrt\" F:\/GIS\/Falklands\/dem_final.tif<\/code><\/pre>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAll working nicely on UTM 21S<\/strong> CRS:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nI’m not too happy having to process a DEM up to three times to get to a clean unified extract of the full dataset, so I’ll keep looking for an alternative, potentially doing it all via GDAL commands. But degradation of the data seems to be kept to a minimum, likley helped by using cubic convolution resampling.<\/p>\n","protected":false},"excerpt":{"rendered":"I didn’t think this was going to be so troublesome! but wanted to note down the steps to resolve. The ‘Build Virtual Raster‘ process in QGIS will not bring together multiple rasters if they span across 2 CRS projections Following my initial post of the issue on GIS stackexchange:https:\/\/gis.stackexchange.com\/questions\/342830\/cant-join-multiple-dems-using-qgis-build-virtual-raster-if-they-span-2-crss A users tip re unifying the … Read More<\/a><\/span><\/p>\n","protected":false},"author":1,"featured_media":1203,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2,4],"tags":[],"_links":{"self":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160"}],"collection":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=1160"}],"version-history":[{"count":22,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions"}],"predecessor-version":[{"id":1216,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions\/1216"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media\/1203"}],"wp:attachment":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=1160"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=1160"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=1160"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
Layers over perfectly:<\/p>\n\n\n\n
Now run Build virtual Raster <\/strong>selecting only the assets that are EPSG:32721<\/strong><\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nFor some reason QGIS can’t render this new vrt<\/strong> very well:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nBut we will push\nforward and use the gdalwarp<\/strong> command to\ncut the new virtual raster above to the square extent created earlier:<\/p>\n\n\n\nNot forgetting to switch the CRS <\/strong>to 32721<\/strong> which is what the virtual raster is set to:<\/p>\n\n\n\ngdalwarp -t_srs EPSG:32721 -wo SOURCE_EXTRA=1000 -tr 12.5 12.5 -srcnodata \"-9999\" -r cubic -ot Float32 -of GTiff -te 229085.941613 4146747.332439 479085.941613 4396747.332439 \"F:\/GIS\/Falklands\/virtual_final.vrt\" F:\/GIS\/Falklands\/dem_final.tif<\/code><\/pre>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAll working nicely on UTM 21S<\/strong> CRS:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nI’m not too happy having to process a DEM up to three times to get to a clean unified extract of the full dataset, so I’ll keep looking for an alternative, potentially doing it all via GDAL commands. But degradation of the data seems to be kept to a minimum, likley helped by using cubic convolution resampling.<\/p>\n","protected":false},"excerpt":{"rendered":"I didn’t think this was going to be so troublesome! but wanted to note down the steps to resolve. The ‘Build Virtual Raster‘ process in QGIS will not bring together multiple rasters if they span across 2 CRS projections Following my initial post of the issue on GIS stackexchange:https:\/\/gis.stackexchange.com\/questions\/342830\/cant-join-multiple-dems-using-qgis-build-virtual-raster-if-they-span-2-crss A users tip re unifying the … Read More<\/a><\/span><\/p>\n","protected":false},"author":1,"featured_media":1203,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2,4],"tags":[],"_links":{"self":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160"}],"collection":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=1160"}],"version-history":[{"count":22,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions"}],"predecessor-version":[{"id":1216,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions\/1216"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media\/1203"}],"wp:attachment":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=1160"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=1160"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=1160"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
For some reason QGIS can’t render this new vrt<\/strong> very well:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nBut we will push\nforward and use the gdalwarp<\/strong> command to\ncut the new virtual raster above to the square extent created earlier:<\/p>\n\n\n\nNot forgetting to switch the CRS <\/strong>to 32721<\/strong> which is what the virtual raster is set to:<\/p>\n\n\n\ngdalwarp -t_srs EPSG:32721 -wo SOURCE_EXTRA=1000 -tr 12.5 12.5 -srcnodata \"-9999\" -r cubic -ot Float32 -of GTiff -te 229085.941613 4146747.332439 479085.941613 4396747.332439 \"F:\/GIS\/Falklands\/virtual_final.vrt\" F:\/GIS\/Falklands\/dem_final.tif<\/code><\/pre>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAll working nicely on UTM 21S<\/strong> CRS:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nI’m not too happy having to process a DEM up to three times to get to a clean unified extract of the full dataset, so I’ll keep looking for an alternative, potentially doing it all via GDAL commands. But degradation of the data seems to be kept to a minimum, likley helped by using cubic convolution resampling.<\/p>\n","protected":false},"excerpt":{"rendered":"I didn’t think this was going to be so troublesome! but wanted to note down the steps to resolve. The ‘Build Virtual Raster‘ process in QGIS will not bring together multiple rasters if they span across 2 CRS projections Following my initial post of the issue on GIS stackexchange:https:\/\/gis.stackexchange.com\/questions\/342830\/cant-join-multiple-dems-using-qgis-build-virtual-raster-if-they-span-2-crss A users tip re unifying the … Read More<\/a><\/span><\/p>\n","protected":false},"author":1,"featured_media":1203,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2,4],"tags":[],"_links":{"self":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160"}],"collection":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=1160"}],"version-history":[{"count":22,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions"}],"predecessor-version":[{"id":1216,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions\/1216"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media\/1203"}],"wp:attachment":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=1160"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=1160"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=1160"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
But we will push\nforward and use the gdalwarp<\/strong> command to\ncut the new virtual raster above to the square extent created earlier:<\/p>\n\n\n\nNot forgetting to switch the CRS <\/strong>to 32721<\/strong> which is what the virtual raster is set to:<\/p>\n\n\n\ngdalwarp -t_srs EPSG:32721 -wo SOURCE_EXTRA=1000 -tr 12.5 12.5 -srcnodata \"-9999\" -r cubic -ot Float32 -of GTiff -te 229085.941613 4146747.332439 479085.941613 4396747.332439 \"F:\/GIS\/Falklands\/virtual_final.vrt\" F:\/GIS\/Falklands\/dem_final.tif<\/code><\/pre>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAll working nicely on UTM 21S<\/strong> CRS:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nI’m not too happy having to process a DEM up to three times to get to a clean unified extract of the full dataset, so I’ll keep looking for an alternative, potentially doing it all via GDAL commands. But degradation of the data seems to be kept to a minimum, likley helped by using cubic convolution resampling.<\/p>\n","protected":false},"excerpt":{"rendered":"I didn’t think this was going to be so troublesome! but wanted to note down the steps to resolve. The ‘Build Virtual Raster‘ process in QGIS will not bring together multiple rasters if they span across 2 CRS projections Following my initial post of the issue on GIS stackexchange:https:\/\/gis.stackexchange.com\/questions\/342830\/cant-join-multiple-dems-using-qgis-build-virtual-raster-if-they-span-2-crss A users tip re unifying the … Read More<\/a><\/span><\/p>\n","protected":false},"author":1,"featured_media":1203,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2,4],"tags":[],"_links":{"self":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160"}],"collection":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=1160"}],"version-history":[{"count":22,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions"}],"predecessor-version":[{"id":1216,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions\/1216"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media\/1203"}],"wp:attachment":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=1160"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=1160"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=1160"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
Not forgetting to switch the CRS <\/strong>to 32721<\/strong> which is what the virtual raster is set to:<\/p>\n\n\n\ngdalwarp -t_srs EPSG:32721 -wo SOURCE_EXTRA=1000 -tr 12.5 12.5 -srcnodata \"-9999\" -r cubic -ot Float32 -of GTiff -te 229085.941613 4146747.332439 479085.941613 4396747.332439 \"F:\/GIS\/Falklands\/virtual_final.vrt\" F:\/GIS\/Falklands\/dem_final.tif<\/code><\/pre>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAll working nicely on UTM 21S<\/strong> CRS:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nI’m not too happy having to process a DEM up to three times to get to a clean unified extract of the full dataset, so I’ll keep looking for an alternative, potentially doing it all via GDAL commands. But degradation of the data seems to be kept to a minimum, likley helped by using cubic convolution resampling.<\/p>\n","protected":false},"excerpt":{"rendered":"I didn’t think this was going to be so troublesome! but wanted to note down the steps to resolve. The ‘Build Virtual Raster‘ process in QGIS will not bring together multiple rasters if they span across 2 CRS projections Following my initial post of the issue on GIS stackexchange:https:\/\/gis.stackexchange.com\/questions\/342830\/cant-join-multiple-dems-using-qgis-build-virtual-raster-if-they-span-2-crss A users tip re unifying the … Read More<\/a><\/span><\/p>\n","protected":false},"author":1,"featured_media":1203,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2,4],"tags":[],"_links":{"self":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160"}],"collection":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=1160"}],"version-history":[{"count":22,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions"}],"predecessor-version":[{"id":1216,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions\/1216"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media\/1203"}],"wp:attachment":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=1160"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=1160"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=1160"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
gdalwarp -t_srs EPSG:32721 -wo SOURCE_EXTRA=1000 -tr 12.5 12.5 -srcnodata \"-9999\" -r cubic -ot Float32 -of GTiff -te 229085.941613 4146747.332439 479085.941613 4396747.332439 \"F:\/GIS\/Falklands\/virtual_final.vrt\" F:\/GIS\/Falklands\/dem_final.tif<\/code><\/pre>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nAll working nicely on UTM 21S<\/strong> CRS:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nI’m not too happy having to process a DEM up to three times to get to a clean unified extract of the full dataset, so I’ll keep looking for an alternative, potentially doing it all via GDAL commands. But degradation of the data seems to be kept to a minimum, likley helped by using cubic convolution resampling.<\/p>\n","protected":false},"excerpt":{"rendered":"I didn’t think this was going to be so troublesome! but wanted to note down the steps to resolve. The ‘Build Virtual Raster‘ process in QGIS will not bring together multiple rasters if they span across 2 CRS projections Following my initial post of the issue on GIS stackexchange:https:\/\/gis.stackexchange.com\/questions\/342830\/cant-join-multiple-dems-using-qgis-build-virtual-raster-if-they-span-2-crss A users tip re unifying the … Read More<\/a><\/span><\/p>\n","protected":false},"author":1,"featured_media":1203,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2,4],"tags":[],"_links":{"self":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160"}],"collection":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=1160"}],"version-history":[{"count":22,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions"}],"predecessor-version":[{"id":1216,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions\/1216"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media\/1203"}],"wp:attachment":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=1160"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=1160"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=1160"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
All working nicely on UTM 21S<\/strong> CRS:<\/p>\n\n\n\n<\/div><\/div><\/div><\/div><\/a><\/div><\/div><\/div><\/div><\/noscript><\/div>\n\n\n\nI’m not too happy having to process a DEM up to three times to get to a clean unified extract of the full dataset, so I’ll keep looking for an alternative, potentially doing it all via GDAL commands. But degradation of the data seems to be kept to a minimum, likley helped by using cubic convolution resampling.<\/p>\n","protected":false},"excerpt":{"rendered":"I didn’t think this was going to be so troublesome! but wanted to note down the steps to resolve. The ‘Build Virtual Raster‘ process in QGIS will not bring together multiple rasters if they span across 2 CRS projections Following my initial post of the issue on GIS stackexchange:https:\/\/gis.stackexchange.com\/questions\/342830\/cant-join-multiple-dems-using-qgis-build-virtual-raster-if-they-span-2-crss A users tip re unifying the … Read More<\/a><\/span><\/p>\n","protected":false},"author":1,"featured_media":1203,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2,4],"tags":[],"_links":{"self":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160"}],"collection":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=1160"}],"version-history":[{"count":22,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions"}],"predecessor-version":[{"id":1216,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions\/1216"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media\/1203"}],"wp:attachment":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=1160"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=1160"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=1160"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
I’m not too happy having to process a DEM up to three times to get to a clean unified extract of the full dataset, so I’ll keep looking for an alternative, potentially doing it all via GDAL commands. But degradation of the data seems to be kept to a minimum, likley helped by using cubic convolution resampling.<\/p>\n","protected":false},"excerpt":{"rendered":"
I didn’t think this was going to be so troublesome! but wanted to note down the steps to resolve. The ‘Build Virtual Raster‘ process in QGIS will not bring together multiple rasters if they span across 2 CRS projections Following my initial post of the issue on GIS stackexchange:https:\/\/gis.stackexchange.com\/questions\/342830\/cant-join-multiple-dems-using-qgis-build-virtual-raster-if-they-span-2-crss A users tip re unifying the … Read More<\/a><\/span><\/p>\n","protected":false},"author":1,"featured_media":1203,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2,4],"tags":[],"_links":{"self":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160"}],"collection":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=1160"}],"version-history":[{"count":22,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions"}],"predecessor-version":[{"id":1216,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1160\/revisions\/1216"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media\/1203"}],"wp:attachment":[{"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=1160"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=1160"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rossedwards.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=1160"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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