[postgis] new Functions/ Function changes

[Timothy H. Keitt]

Also there's always http://www.google.com/search?q=computational+geometry

T.

Dave Blasby wrote:

>CVS version has some new OpenGIS functions (and a few changes).
>
>Comming soon is a bunch of testing, then a release (not sure exactly
>when).  
>After that, I'll go over the OpenGIS spec and see where we are not
>compliant.  I'd appreciate other peoples help on that.
>Then, its on to doing the complicated spatial operations.  Hopefully
>we'll be using JTS since Martin (and vividsolutions) have spent a lot of
>time and talent getting the spatial operators/functions robust.
>
>
>Length2d() is renamed length()
>perimeter2d() is renamed to perimeter()
>
>numgeometries(geometry) works on MULTI* types
>geometryn(geometry) works on MULTI* types
>
>
>from section 2.1.5.1
>--------------------
>startpoint(geometry) :- if geometry is a linestring, return the first
>point.  Otherwise, return NULL.
>
>endpoint(geometry) :- if geometry is a linestring, return the last
>point.  Otherwise, return NULL.
>
>from section 2.1.9.1/3.2.18.2
>--------------------
>
>centroid(geometry) :- if geometry is a polygon (or multipolygon), return
>the mathematical centroid (no guaranteed to be on polygon), otherwise
>return NULL. I define centroid as the average location of all the points
>in the polygon (outer ring only).  For multipolygons, average all the
>points on all the outer rings.
>
>from section 3.2.12.2/3.2.17.2
>---------------------
>isclosed(geometry) :- if geometry is a linestring then returns 
>startpoint == endpoint.  If its not a linestring then return NULL.  If
>its a multilinestring, return true only if all the sub-linestrings have
>startpoint=endpoint.
>
>
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> 
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>
>

-- 
Timothy H. Keitt
Department of Ecology and Evolution
State University of New York at Stony Brook
Stony Brook, New York 11794 USA
Phone: 631-632-1101, FAX: 631-632-7626
http://life.bio.sunysb.edu/ee/keitt/




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