Compute partial polygon area

[Krung Saengpole]

Hi Steve,
   
  Thank you for your advice. I re-tried postgis again, it worked with a little debug message but not the case. I confused with postgresql and postgis geometry features. Could you please show me circleAsPolygon() function (user-defined)?
   
  TIA
  Krung
   
  >> I'd like to compute partial area of polygon that intersects with 
another 
> polygon. Is there a way to do with PHPMapscript? For example, I want 
to 
>> know how many square kilometers of forests that reside in the area of 
>> 50km-radius circled area. Or where can I get to the example?
   
  >If you use PostGIS this is a straight forward SQL query like:
  >select polyid, area2d(intersection(the_geom, circleAsPolygon(point(x, 
y), radius, npoints)) as area from mytable where the_geom && 
expand(point(x, y), radius);
  >where the_geom is the geometry column for the polygons
and x,y is the center of your circle radius = 50000
>and npoints is the number of points to generate for the polygonal 
circle.
  >you would need to write a function circleAsPolygon() in pgsql, but that 
is pretty trivial and most of us that would with PostGIS could post 
>that 
>if you needed us to.
  >-Steve

			
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