mandragara wrote:I'm able to merge the areas of interest into a virtual raster and then process that as a big chunk in QGIS, but there's a file limit so I can't process a ton. I can use a command to merge them all as a TIFF but the output is much larger than the .asc files that go into making it. A TIFF that covers all of the Greater Blue Mountains would be 11 terabytes or so. I'm investigating if there's a way of merging the raw .asc files.
Go the other way. I have hierarchies of virtual rasters, and then I just process the area of interest.
I have a virtual raster (of virtual rasters, of 2x2km GeoTIFFs) which stretches from south of Ulladulla to north of Maitland, and west to the edge of the Blue Mountains. All up there are around 10000 files and 90GB.
I will progressively write up how to put one of these together and how to use it - but the core information is already up:
https://maps.ozultimate.com/wiki/nsw_dems
You can then use PyQGIS to clip and load an area of interest, as long as it's not too large (not sure what size that is!). Download a GeoJSON of the area (using say the polygon tool in https://maps.ozultimate.com/), and then run the following at the Python Console (replacing any file paths with your own):
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resultClip = processing.runAndLoadResults("gdal:cliprasterbymasklayer", { 'ALPHA_BAND' : False, 'CROP_TO_CUTLINE' : True, 'DATA_TYPE' : 0, 'EXTRA' : '', 'INPUT' : 'E:/geodata/nsw100k.vrt', 'KEEP_RESOLUTION' : False, 'MASK' : 'C:/Users/brennant/Downloads/data.geojson', 'MULTITHREADING' : False, 'NODATA' : None, 'OPTIONS' : '', 'OUTPUT' : 'TEMPORARY_OUTPUT', 'SET_RESOLUTION' : False, 'SOURCE_CRS' : None, 'TARGET_CRS' : None, 'X_RESOLUTION' : None, 'Y_RESOLUTION' : None })