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I have a few large LiDAR DEMs that I want to merge. Each DEM has some glitches around the borders which need to be removed in order to get a seamless final product. I manually traced around each DEM to create a polygon which excludes the glitchy areas. I am using gdalwarp to clip the raster files, but I am experiencing very slow performance.
The rasters are between 3 and 10 GB, which I understand is pretty big… however I have ~3 ghz of processing power & 4GB of RAM. These rasters load into QGIS quickly and are quick to refresh. I can derive a hillshade or slope raster from one of these DEMS in 2 or 3 minutes.. so it seems unreasonable when it takes 4-6 HOURS to clip one of these rasters with gdalwarp.
Can anybody offer an explanation of what might be going on?
I am also bothered by the very large file sizes (up to 4x larger than the original) which result from the clipping. Research suggests that this is a compression issue, but gdalinfo does not return any compression info for any of the original rasters, and even when I compress the files are still 2x larger than the originals. Could there be any reason for this other than compression?