Krung Saengpole wrote:
Hi all,
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
