[Qgis-user] New User: Cropping makes HUGE files (and I know about COMPRESS-LZW)

[Alex M]

The Clipper dialog is missing GUI options to set the compression. In the
box at the bottom, edit the command to add the following "-co
COMPRESS=DEFLATE -co PREDICTOR=2 -co ZLEVEL=9"

That will apply compression to the output.

Thanks,
Alex

On 03/09/2018 01:44 PM, Dennis Grant wrote:
> Hi all, I have a very specific problem I'm attempting to solve, and I'm sad
> to say it has defeated me.
> 
> What I am trying to do is generate a 3D model of the terrain relief in a
> certain area so that it can be fed into a CNC machine for subsequent
> carving.
> 
> So then, step 1 - get a DEM GEOTIFF from EarthExplorer: done.
> 
> Here's the thumbnail
> https://earthexplorer.usgs.gov/browse/srtm_v3/1arc/w067/n45_w067_1arc_v3.jpg
> (but I have the actual GEOTIFF too - I know that the thumbnail is not the
> GEOTIFF)
> 
> Now what I need to do is crop the area covered by the GEOTIFF down to the
> roughly 4 sq km area I want to model.
> 
> So I downloaded and installed qgis for Linux. Add new raster layer using
> the downloaded GEOTIFF, and that comes in fine.
> 
> Problem: I can't narrow down the exact area I need. So I installed the
> OpenStreetMap plugin and added an OSM layer. Happily, the OSM layer and the
> GEOTIFF raster layer line up as expected. So I'm able to adjust the zoom
> window to the area I want to carve.
> 
> I go to Raster: Extraction: Clipper. Input file is the downloaded DEM
> GEOTIFF. Output file is a filename I pick for the extract. I select the
> area I want, and I see that it builds a command line for gdal_translate
> accordingly. OK, I get it, QGIS is a graphical front end for command line
> tools - that's a common Linux method for building applications. Seen that
> before. No worries.
> 
> So then I execute, and after 10 minutes, it still isn't done, and the file
> it is building is almost a gigabyte in size.
> 
> Stop process, google for "qgis extract huge files" and I find that the
> issue is likely compressed vs uncompressed TIFF, and there are a couple of
> options to feed gdal_translate to turn on compression (via the little
> pencil icon) OK, add that, and set it off.
> 
> Come back an hour later, still not done, and the file is 150 Gb in size.
> 
> Something is not right. The base GEOTIFF is 25 Mb. A drastically cropped
> version - even uncompressed - should not be that large.
> 
> This happens even if I delete the OSM layer.
> 
> What is going on here? What have I missed?
> 
> DG
> 
> 
> 
> _______________________________________________
> Qgis-user mailing list
> Qgis-user at lists.osgeo.org
> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
>