<HTML dir=ltr><HEAD><TITLE>Re: [postgis-devel] ST_MakePolygon returns null geometrywhen passedNULL or empty array</TITLE>
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<DIV dir=ltr><FONT face=Arial color=#000000 size=2>Well on the list of priorities, its pretty low on the totem pole at least for me and I'm not even sure its a desirable thing to do without some configuration switch if there is a cost penalty. I think a simple note in the docs that these functions will not guarantee validity is sufficient and if they want to throw out invalid results they should do an after processing ST_IsValid check.</FONT></DIV>
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<DIV dir=ltr><FONT face=Arial size=2>I think as long as people are aware of it, that's probably good enough. Just don't want people thinking because PostGIS lets you do it, then it is valid. </FONT></DIV>
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<DIV dir=ltr><FONT face=Arial size=2>Its actually kind of perversely comforting to know that I can create creatures that can't sustain life. Almost as fun as working in a molecular biology lab again, but less dangerous.</FONT></DIV>
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<DIV dir=ltr><FONT face=Arial size=2>Thanks,</FONT></DIV>
<DIV dir=ltr><FONT face=Arial size=2>Regina</FONT></DIV></DIV>
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<FONT face=Tahoma size=2><B>From:</B> postgis-devel-bounces@postgis.refractions.net on behalf of Kevin Neufeld<BR><B>Sent:</B> Wed 7/9/2008 12:11 PM<BR><B>To:</B> PostGIS Development Discussion<BR><B>Subject:</B> Re: [postgis-devel] ST_MakePolygon returns null geometrywhen passedNULL or empty array<BR></FONT><BR></DIV>
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<P><FONT size=2>As a geometry constructor, this method is similar to the WKT or WKB<BR>parser which don't currently test for validity. As MarkC pointed out a<BR>few emails ago (in the "Removing geometry parsing checks" thread),<BR>isvalid() calls are heavyweight and expensive to make.<BR><BR>Oh the other hand, this method is fundamentally different than the WKT/B<BR>parser in that it's highly unlikely to be used in any sort of bulk<BR>loading. So maybe the performance hit for testing for validity (and<BR>throwing a NOTICE if necessary) is not so bad? It would probably be the<BR>only geometry constructor that tests for validity though.<BR><BR>Cheers,<BR>Kevin<BR><BR>Obe, Regina wrote:<BR>> On the robust side of things should we be concerned that if we feed it<BR>> closed line strings that are not contained in the shell (or is the<BR>> shell) and/or overlap each other. The function happily returns you an<BR>> invalid geometry.<BR>><BR>> SELECT ST_IsValid(the_geom), ST_AsText(the_geom)<BR>> FROM (<BR>> SELECT ST_MakePolygon(<BR>> 'LINESTRING(0 0, 0 8, 8 8, 8 0, 0 0)'::geometry,<BR>> ARRAY['LINESTRING(0 0, 0 8, 8 8, 9 0, 0 0)'::geometry]) AS the_geom<BR>> ) AS foo;<BR>><BR>> seems like it should give you a NOTICE or something.<BR>><BR>_______________________________________________<BR>postgis-devel mailing list<BR>postgis-devel@postgis.refractions.net<BR><A href="http://postgis.refractions.net/mailman/listinfo/postgis-devel">http://postgis.refractions.net/mailman/listinfo/postgis-devel</A><BR></FONT></P></DIV></BODY></HTML>
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