I agree with you Hamish, I didn't thought about increasing data sets and hidden information. But still, I think that if you know what you are doing, and you do it without erasing the original file (increasing need for storage -which is the same problem as the index) it might be a simple solution (i.e. not introducing any other file) that can improve speed. Is speed improvement the only virtue of spatial indexing, or am I wrong ?<br>
<br>Etienne<br><br><div class="gmail_quote">On Wed, Apr 22, 2009 at 6:18 AM, Hamish <span dir="ltr"><<a href="mailto:hamish_b@yahoo.com">hamish_b@yahoo.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br>
just a small argument against re-ordering data.<br>
<br>
the raw order gives some information re. time of sample and direction of<br>
travel for a cost of 0 bytes. if the instrument or navigation goes a bit<br>
wonky for a short while and this is not noticed until late in the post-<br>
processing stage (when you're pouring through the data) it provides an<br>
efficient method or slicing out a chunk of data from a specific length<br>
of that specific transect. if your swaths overlap and you removed the<br>
raw order, the best you could do would to be to chop by geographical<br>
extent, even for the swaths which overlap the region which are fine.<br>
<br>
also anything that introduces memory or processing time overheads must<br>
be built in a way that will scale to much larger datasets than we have<br>
today (but might in 5 years time, when hopefully this fine library is<br>
still in active use)<br>
<br>
<br>
<br>
Also, I've been meaning to send a note about the C/C++ ABI stability<br>
issues. There was a thread on the DebianGIS list about GDAL's C/C++<br>
ABI and who should link to what. The result was that the C ABI was<br>
heavily favoured for external apps to use even though internally<br>
GDAL is written in C++. Maybe it is just GDAL specific -- you can read<br>
Frank's comments at the following link, possibly it gives you some ideas<br>
for how to handle this in libLAS.<br>
<br>
<a href="http://thread.gmane.org/gmane.comp.gis.grass.pkg.general/1230/focus=1286" target="_blank">http://thread.gmane.org/gmane.comp.gis.grass.pkg.general/1230/focus=1286</a><br>
<br>
<br>
regards,<br>
<font color="#888888">Hamish<br>
</font><div><div></div><div class="h5"><br>
<br>
<br>
<br>
<br>
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