<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>I do not see that you specified that the output TIFF image be tiled</div><div><div>-co TILED=YES -co BLOCKXSIZE=512 -co BLOCKYSIZE=512</div><div>gdal_merge.py supports the -v input option that reports progress as a % for every source image merged into the destination image. </div></div><div><div>It is better to do the initial gdal_merge.py uncompressed, and then follow that with a gdal_translate to created a compressed file.</div></div><div>Greg</div><br><div><div>On Jul 16, 2010, at 9:19 PM, Leith Bade wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">Hi,<div><br></div><div>I am trying to use gdal_merge to mosaic a very large topo GeoTIFF set.</div><div><br></div><div>Uncompressed the data set is 60GB, but I keep it stored with DEFLATE compression which results in a dataset under 10GB.</div>
<div><br></div><div>Mosaicked the uncompressed file will be 125GB because of the large regions of nodata generated. Unfortunately this is too big to store on my HDD so I need to apply DEFLATE to it as well.</div><div><br>
</div><div>I am experimenting with only 1/2 the data set at the moment with this command:</div><div>gdal_merge -co COMPRESS=DEFLATE -co ZLEVEL=9 -co BIGTIFF=YES -o NI-50.tif *-00.tif</div><div><br></div><div>On my AMD Phenom II X4 @ 3.2GHz, 64 bit Windows 7, 4GB DDR3 CAS-7 RAM (basically a decently specced PC gaming machine)</div>
<div>it has been running for 16 hours and so far has only made it 60% (124 of 204 files)</div><div><br></div><div>The other issue is so far the file is 54GB so I will likely run out of disc space before it finished. This indicates that no DEFLATE compression is happening at all!</div>
<div><br></div><div>It currently maxing only 1 CPU core, so I assume it is trying to run DEFLATE then somehow failing to compress at all?</div><div><br></div><div>Looking at gdal_merge.py I think the major performance issue is the order in which it copies the data. Currently it copies an entire image at a time (1 colour channel at a time). Thus DEFLATE will not work due to the rather random write pattern to each scanline.</div>
<div><br></div><div>I think a much faster method would be to calculate the destination rectangles for each file into some sort of list. Aftter this generate the destination file 1 scanline at a time, calculating which source images intersect, and working left to right filling with solid color or copying scanlines from the source image.</div>
<div><br></div><div>This allows the DEFLATE to work far more effciently as the write pattern is horizontally linear.</div><div><br></div><div>What are your views/suggestions/etc.?</div><div><br clear="all">Thanks,<br>Leith Bade<br>
<a href="mailto:leith@leithalweapon.geek.nz">leith@leithalweapon.geek.nz</a><br><br>
</div>
_______________________________________________<br>gdal-dev mailing list<br><a href="mailto:gdal-dev@lists.osgeo.org">gdal-dev@lists.osgeo.org</a><br>http://lists.osgeo.org/mailman/listinfo/gdal-dev</blockquote></div><br></body></html>