Expose PointInPolygon and other helpers

[thomasp85]

While my own interest is mainly in PointInPolygon, there are other helpers which would be nice to have access to from R, such as Area, Poly2ContainsPoly1, and IntersectPoint

[baddstats]

This has been put on the to-do list..

[thomasp85]

Perfect - thanks.

Do you have any idea of a time-frame (not being pushy - just out of interest)

[baddstats]

PointInPolygon is now exposed (through new function pointinpolygon)

[baddstats]

Uh-oh,..., Poly2ContainsPoly1 seems to be incorrect. The code tests whether every vertex of Poly1 lies inside Poly2 but this doesn't deal with cases where an edge of Poly1 crosses outside Poly2. I will investigate whether this has been fixed in later versions of Clipper, and update.

[mpadge]

To avoid opening a new issue, may I request another extension of PointInPolygon, via vectorization of polygons to return a matrix of [npoints, npolygons] (or the other way around)?

I also concur with @thomasp85 that it would be helpful to expose other clipper fns, with my choice being to use area in an extension of the main ClipperLib::Clipper::Execute routine to calculate overlap areas? I suspect a great many people using the main polyclip routine would do so because they are interested in areas of overlap, and since the Clipper::Area function directly accepts the Paths object from the solution to the clip, it would be much more efficient if that could be extended within the C++ code, like this:

# set up layer1, layer2
areas <- polyclip_areas (layer1, layer2)
head (areas)
# area1   area2
# 1 456   123
# 2 ...

where area1 is just the area of the "subject polygon" (in AJ's terminology); area2 comes straight from the clipper solution in each instance; and the units can be directly re-scaled with your eps value, because clipper::Area returns a <double>.