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

[Alex M]

Can you supply the bounding box you are using (or the full command).

Also which version of QGIS on which OS?

You are correct that something is odd.

Thanks,
Alex

On 03/09/2018 02:04 PM, Dennis Grant wrote:
> I did that, and I got a file that was 150 Gb (and still growing after an
> hour)
> 
> On Fri, Mar 9, 2018 at 6:01 PM, Alex M <tech_dev at wildintellect.com> wrote:
> 
>> 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
>>>
>>
>>
>