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<font face="Helvetica, Arial, sans-serif">Hi all,<br>
<br>
Martin, sounds clear to me, but what's the deal with the intersection?
>From my experience, when I buffer 50 line segments, I get 50 buffers
(i.e 50 "rows"). So no intersection is made between the several
buffers, as far as I can see. Please correct me if I'm wrong.<br>
<br>
reagrds,<br>
alex.<br>
</font><br>
Martin Davis wrote:
<blockquote
cite="mid5A94289A9268514C8D6C0F1FF44BA0274F4F4E@venus.VividSolutions.com"
type="cite">
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<div><span class="204313117-12032004"><font face="Arial"
color="#0000ff" size="2">The performance difference is probably due to
the difference in the buffer widths. In general, larger buffer widths
require longer to compute than smaller ones. This is due to the
greater interaction (intersections) between the offset curves computed
to build the buffer curve.</font></span></div>
<div> </div>
<div> </div>
<div align="center"><font face="Arial" size="2">Martin Davis, Senior
Technical Architect<br>
<strong><font color="#0000ff">Vivid Solutions Inc.</font></strong><br>
<em>Suite #1A-2328 Government Street Victoria, B.C. V8T 5G5<br>
Phone: (250) 385 6040 - Local 308 Fax: (250) 385 6046</em></font></div>
<blockquote
style="border-left: 2px solid rgb(0, 0, 255); padding-left: 5px; margin-left: 5px; margin-right: 0px;">
<div class="OutlookMessageHeader" lang="en-us" dir="ltr"
align="left"><font face="Tahoma" size="2">-----Original Message-----<br>
<b>From:</b> Alexander Pucher
[<a class="moz-txt-link-freetext" href="mailto:pucher@atlas.gis.univie.ac.at">mailto:pucher@atlas.gis.univie.ac.at</a>] <br>
<b>Sent:</b> Friday, March 12, 2004 3:39 AM<br>
<b>To:</b> PostGIS Users Discussion<br>
<b>Subject:</b> [postgis-users] Buffer Performance<br>
<br>
</font></div>
<font face="Helvetica, Arial, sans-serif">Hi,<br>
<br>
did some buffer performance testing with a table that holds about 2100
multilinestrings (river network of europe).<br>
<br>
'select buffer(the_geom,5) from river;'<br>
<br>
takes about 7 seconds to execute, whereas<br>
</font><font face="Helvetica, Arial, sans-serif"><br>
'select buffer(the_geom,15000) from river' <br>
<br>
takes a couple of minutes...<br>
<br>
The 'river' table is not indexed, if this might be of importance ?!?<br>
<br>
'explain select....' <br>
<br>
shows similar output for both queries:<br>
<br>
QUERY PLAN<br>
-----------------------------------------------------------<br>
Seq Scan on river (cost=0.00..139.51 rows=2051 width=32)<br>
(1 row)<br>
<br>
<br>
What's the reason for the difference in execution time, depending on
the buffer size?<br>
Is there a way to speed up </font><font
face="Helvetica, Arial, sans-serif">execution time of </font><font
face="Helvetica, Arial, sans-serif">such queries??<br>
<br>
Best regards,<br>
alex.<br>
</font><font face="Helvetica, Arial, sans-serif"><br>
</font></blockquote>
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