Making perpendicular lines through each polygon edge using PostGIS?

I have polygons and lines I would like to make perpendicular lines through each polygon edge so I can find intersections with other polygons and lines.

Answer

Assuming that you have PostGIS knowledge, this is one way forward:

• Take the ExteriorRing from your polygon (results in a linestring)


• Make seperate segments out of your ExteriorRing (use this example from Paul Ramsey)


• Create parallel lines with ST_OffsetCurve with a desired distance D on the correct side (your polygons vertices should always have the same direction, use ST_ForceRHR when they don't)


• For every segment, make a new line from the centroid of that segment to the centroid of the corresponding parallel line with ST_MakeLine

Now you should have your perpendicular lines with a length D starting from the sides of your polygon.