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--- nsw_dems [2021/02/10 08:23] – created bushwalking
+++ nsw_dems [2021/05/04 18:25] – [Pre-processing data] bushwalking
@@ Line 1: / Line 1: @@
-====== Managing DEMs ======
+====== Managing large DEMs ======
-===== Downloading data =====
+===== Intro =====
 While data can be downloaded in an ad hoc manner, if you are regularly processing DEMs, it is better to have the DEM tiles already downloaded.
+Once downloaded, pre-process the tiles into GeoTIFFs, build a virtual raster for each 1:100k grid square. You can then build a virtual raster of virtual rasters!
+===== Downloading data =====
 Download tiles by 1:100k map area, which is 0.5 x 0.5 degree squares. Each 1:100k map area ranges from around 2GB to 6GB of data, depending on the number of 2m DEMs vs 1m DEMs, and other factors.
@@ Line 153: / Line 157: @@
 New-Item "$targetFolder\input.txt"
 Get-ChildItem -Path "$targetFolder\*.tif" | Add-Content "$targetFolder\input.txt"
-&"gdalbuildvrt.exe" -resolution lowest -input_file_list "$targetFolder\input.txt" "$targetFolder\temp.vrt"
+&"gdalbuildvrt.exe" -resolution user -tr 2 2 -input_file_list "$targetFolder\input.txt" "$targetFolder\temp.vrt"
 </file>
-It is possible to then build a larger virtual raster from the individual 1:100k virtual rasters.
+You can rename temp.vrt to anything you like, but it needs to stay relative to the GeoTIFF files.
+It is possible to then build a larger virtual raster from the individual 1:100k virtual rasters. Note that larger rasters need to have the same projection. Also keep in mind that not all data is at 2m resolution.
 ===== Loading data =====