Alexandre,<br><br>Your straight forward method is the best.<br><br>PostGIS takes care of optimization using rectangular bounding boxes.<br>Union function works best if you use it as an aggregate function. In OGR, you can use OGRGeometry::UnionCascaded() by passing a OGRGeometryCollection object to it.<br>
<br><br><div class="gmail_quote">On Fri, Jun 10, 2011 at 12:58 AM, Alexandre Gacon <span dir="ltr"><<a href="mailto:alexandre.gacon%2Bgdal@gmail.com">alexandre.gacon+gdal@gmail.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;">
Hi,<div><br></div><div>I am using GDAL/OGR to find the links under a set of towns, on the whole France territory.</div><div><br></div><div>My links and my towns are stored on a Postgis database.</div><div><br></div><div>For the moment I use the most precise request I can:</div>
<div><br></div><div>- I make a union of all the polygons of the towns I am interested in</div><div>- I send a request with GDAL to the Postgis database to get the links covered by the geometry</div><div>- I read the result</div>
<div><br></div><div>Would it be faster if I make a request for each town, instead of making the union of the geometries ?</div><div><br></div><div>Would it be faster if I use a simple spatial filter (like a rectangle) instead of the precise geometry ?<br clear="all">
<br>-- <br>Alexandre Gacon<br>
</div><br clear="all"></blockquote></div><br>-- <br>Best regards,<br>Chaitanya kumar CH.<br>/tʃaɪθənjə/ /kʊmɑr/ <br>+91-9494447584<br>17.2416N 80.1426E<br>