Dear all, please, I am looking to understand how the two functions ("inpolygon ()" and "boundary()") work ?

Dear all, Please, I have a question: I know the function "inpolygon()" give me a logical result if a data point inside or outside a polygon and "boundary()" give me the data points on the border of a shape. But how these two algorithms work ?

Please, I need to understand them.

Kind regards Ammar

Answer 1

[KSSV]

From a given point P, the code draws a straight onto the given polygon. If this line intersects even number of times then the point lies outside the polygon, if the line intersects odd number points then points lies inside the polygon. The code is based on the refer article:

http://ac.els-cdn.com/S0925772101000128/1-s2.0-S0925772101000128-main.pdf?_tid=369ef44e-d7eb-11e6-b220-00000aab0f01&acdnat=1484131771_c505af2dfb8307ef1d0f8eef55733999

For outline refer:

https://en.wikipedia.org/wiki/Point_in_polygon

[Ammar]

Dear KSSV, I would like to thank you for this answer. Please, what about the function "boundary()" how it is work ? Kind regards Ammar

[KSSV]

It uses convexhull I guess....you can see the inbuilt function. Type edit boundary and read the code part and documentation given out there.