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<p class="MsoNormal"><span lang="EN-US">Hello list,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">While executing old scripts today I noticed that the behavior of the function ST_PointN has changed between postgis 1.5 and 2.0<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">When the function is used on a MULTILINESTRING the behavior is not the same and it looks like a bug in 2.0 I think.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">The doc says :<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">“”ST_PointN — Return the Nth point in the first linestring or circular linestring in the geometry. Return NULL if there is no linestring in the geometry.””<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">(<a href="http://postgis.refractions.net/documentation/manual-2.0/ST_PointN.html">http://postgis.refractions.net/documentation/manual-2.0/ST_PointN.html</a>)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">So when I call the function on a MULTILINESTRING I expect it to return the Nth point of the first linestring.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">In postgis 1.5 it’s the case but in 2.0 it returns null.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Example :<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">select st_astext(st_pointn(st_geomFromText('MULTILINESTRING((0 0, 1 1, 2 2))'), 2));<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Result in postgis 1.5 (PostgreSQL 9.1)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">"POINT(1 1)"<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Result in postgis 2.0 (postgreSQL 9.2)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Null<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I could fix my script by merging my multi into single geometries but I think that either the doc or the behavior of the function should be updated.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Nicolas.<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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