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autocad-pluginobjectarx

How can I check if line or point is inside or outside of area

In ModelSpace I have an area limited by some curves (joined them to have AcDbRegion).

I have also drawn AcDbLine.

What I need is to split line to get lines only inside area.

I know how to get intersection points, but how can I find if line conecting two intersection points is inside? or outside area?

Solution

  • If you want to do it manually (with an algorithm that will work with any APIs), I would suggest you use the "winding number algorithm" for the purpose of Point In Polygon calculation. It does not take in consideration bulges in the polygon, but it is very fast is implemented properly allowing me to beat AutoCAD's API by a fold of 2x.

    Another possibility, is to draw a temporary line from the point you are testing to infinity, and test how many intersection it has with your polyline. If the number of intersections is odd, then you are inside the polyline; if it is even, then you are outside of the polyline. If the intersection testing is done with the API of the application, it should take in consideration the bluges in the polyline vertices.