[postgis-users] How is Centroid(Geometry) calculated?

[TECHER David]

Hi Matt,

It you want a point always inside your geometries use pointonsurface() 
instead.

The centroid is not always on the geometries

it deals with the "convexity/concavity" of your geometries
Matt Doughty a écrit :
>
> Hi,
>
> Can anybody explain how PostGIS calculates centroids? I’ve checked the 
> manual but the relevant section doesn’t refer to an OGC Specification. 
> From what I can understand, it takes an average of the coordinates of 
> all the vertices of an entry, ignoring whether or not the centroid 
> falls outside the polygons. Is this right? This differs from other 
> GIS- GeoMedia, for example, when confronted with a multipolygon entry, 
> always puts the centroid inside the largest polygon.
>
> Can anybody shed some light on this?
>
> Cheers,
>
> Matt
>
> Matt Doughty
>
> 	
>
> GEOGRAMA S.L.
>
> Tel.: +34 945 13 13 72 652 77 14 15
>
> Fax: +34 945 23 03 40
>
> www.geograma.com
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> postgis-users mailing list
> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users
>   


	

	
		
___________________________________________________________________________ 
Yahoo! Mail réinvente le mail ! Découvrez le nouveau Yahoo! Mail et son interface révolutionnaire.
http://fr.mail.yahoo.com