<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div>On Apr 5, 2010, at 12:33 PM, Matt Klaric wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><br><div class="gmail_quote">On Mon, Apr 5, 2010 at 2:20 PM, William Kyngesburye <span dir="ltr"><<a href="mailto:woklist@kyngchaos.com">woklist@kyngchaos.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
I thinking of creating a vrt for approx 19000 geotiff DEM tiles (SRTM). Any comments on the performance or practicality of this? Is there a difference in performance between Geotiff and GRASS as the tile format?<br>
<br>
Mainly it's so I can easily extract regions for projects, so it would be one-shot gdal_translate runs.<br><br></blockquote><div><br>I've done something similar. <br><br>Check out the SourceProperties tag in
<a href="http://www.gdal.org/gdal_vrttut.html">http://www.gdal.org/gdal_vrttut.html</a>. If you specify that for each source image, then GDAL doesn't have to open all 19000 images at runtime. The performance is quite good. <br></div></div></blockquote></div><br><div>Looking at the vrt from the file I built with my drg images, I have this:</div><div><br></div><div><div> <SimpleSource></div><div> <SourceFilename relativeToVRT="1">./barrett_canyon/o39117a4.tif</SourceFilename></div><div> <SourceBand>1</SourceBand></div><div> <SourceProperties RasterXSize="4463" RasterYSize="5710" DataType="Byte" BlockXSize="4463" BlockYSize="1"/></div><div> <SrcRect xOff="0" yOff="0" xSize="4463" ySize="5710"/></div><div> <DstRect xOff="92733" yOff="134498" xSize="4473" ySize="5723"/></div><div> </SimpleSource></div><div><br></div><div>So, presumably, gdalbuildvrt generates this for you. Is there something missing here to achieve what you are talking about, Matt?</div><div><br></div><div>Thanks,</div><div>John</div></div></body></html>