I have got the point and the polygon (or line). I have to find the closest coordinate (it can be the "virtual" point on edge) from polygon due to the point.
Do you know how to find out this coordinate?
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This should work http://postgis.net/docs/ST_ClosestPoint.html
ST_ClosestPoint — Returns the 2-dimensional point on g1 that is closest to g2. This is the first point of the shortest line.