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<DIV><FONT size=2><FONT size=3><FONT size=2>Hi.</FONT></FONT></FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2> I don't know OGC spec.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2> But I have a couple of questions about your getting
centroids method.</FONT></DIV>
<DIV><FONT size=2><FONT size=3><FONT size=2></FONT></FONT></FONT> </DIV>
<DIV><FONT size=2><FONT size=3><FONT size=2> Do you consider concave
polygons for calculating centroids? For some of them, centroids by "<FONT
size=3>average location </FONT>" maybe exist outside of polygons.
</FONT></FONT></FONT></DIV>
<DIV><FONT size=2><FONT size=3><FONT size=2></FONT></FONT></FONT> </DIV>
<DIV><FONT size=2><FONT size=3><FONT size=2> <FONT size=3>For
multipolygons, "average all the points on all the outer rings" doesn't seem to
always exist within multipolygons. If not, in some cases, centroids will exist
within smaller ones of multipolygons. I don't think smaller polygon's
centroid is representative of multipolygon without any other info or
knowledge, for example, Vancouver Island, which has Province capital,
Victoria, in BC province .</FONT></FONT></FONT></FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2><FONT size=3><FONT size=2><FONT size=3> I think larger
polygon should has a centroid within a
multipolygon.</FONT><BR></DIV></FONT></FONT></FONT>
<DIV><FONT size=2><FONT size=3><FONT size=2> </DIV></FONT>
<DIV><FONT size=2> How do you think?</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><BR>Dave Blasby wrote:<BR><BR>>from section
2.1.9.1/3.2.18.2<BR>>--------------------<BR>><BR>>centroid(geometry)
:- if geometry is a polygon (or multipolygon), return<BR>>the mathematical
centroid (no guaranteed to be on polygon), otherwise<BR>>return NULL. I
define centroid as the average location of all the points<BR>>in the polygon
(outer ring only). For multipolygons, average all the<BR>>points on all
the outer rings.<BR>><BR><BR></DIV></FONT></FONT>
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