<html xmlns="http://www.w3.org/1999/xhtml"><head><title></title></head><body><div>I do specify -i 20 in my scripts (that was a typo just in my original email). Does it still work ok for you with an interval of 20 instead of 100?
</div><div><br></div><div>I’m actually doing more tests just now. I’ve found that gdal_contour is significantly faster with a far smaller output shape file size if I first reproject to EPSG:3785 using gdalwarp, e.g
</div><div>gdalwarp -s_srs EPSG:4326 -t_srs EPSG:3785 -r bilinear srtm_36_02.tif srtm_36_02_rp.tif<br>
</div><div><br></div><div>Then contour extraction with
</div><div>gdal_contour -a elev -snodata 32767 -i 20 srtm_36_02_rp.tif srtm_36_02_contours.shp<br>
</div><div><br></div><div>Interestingly if I gdalwarp then gdal_merge the contour processing is still pretty fast (but with the artifacts of bilinear warping).
</div><div>But if I first merge, then reproject with gdalwarp then the processing is very slow, or fails due to the ~4GB limit
</div><div><br></div><div>Not entirely sure what is going on, but I’ll put together a script to demonstrate the different issues.
</div><div><br></div><div>Tom
</div><div><br></div><div><br></div><blockquote type="cite"><div>On Mar 24, 2014, at 1:41 PM, Jukka Rahkonen <jukka.rahkonen@mmmtike.fi> wrote:
</div><div><br></div><div>Jukka Rahkonen <jukka.rahkonen <at> mmmtike.fi> writes:
</div><div><br></div><blockquote><div><br></div><div>Tom Beddard <tom <at> subblue.com> writes:
</div><div><br></div><div><br></div><blockquote><div>Can anyone else confirm this behaviour when extracting contours from
</div><div><br></div></blockquote><div>merged SRTM tiles?
</div><div><br></div></blockquote><div><br></div><div>Can you check this command, it is perhaps not that you actually used:<br>gdal_contour -a elev -snodata 32767 -i uk-3785.tif uk-contour.shp
</div><div><br></div><div>My GDAL gives FAILURE: Neither -i nor -fl are specified.<br>With -i 100 I have managed to run your commands. Result was 620 MB shapefile<br>with 135020 linestrings and it took several minutes to run it but it worked<br>for me.
</div><div><br></div><div>-Jukka Rahkonen-
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