Add Holes Into Polygons about flatten-js HOT 4 CLOSED

Hi @frastlin

Of cause polygon in this library supports holes.

In order to be displayed as a hole, face should be simply placed inside another face - "island".

But if you want to distinguish between islands and holes in algorithms, like area measurement, inclusion check or boolean operations, islands and holes should have opposite orientations: for instance, if islands are oriented clockwise (Flatten.ORIENTATION.CW), holes have to be oriented counter clockwise (Flatten.ORIENTATION.CCW).

If you are not sure which orientation the face has, use this code to detect and, if need, revert orientation:

let face = polygon.addFace(points.map(([x, y]) => new Point(x, y)));
 if (face.orientation() !== Flatten.ORIENTATION.CCW) {
    face.reverse();
 }

Note, that when orientation calculated, axe Y is considered to direction from down up, like in math.

Best regards,
Alex Bol

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OK, I can't seem to make this work with the contains(point) or distanceTo algorithm. if I do a distanceTo algorithm in the middle of a hole, it should give me the distance to the nearest points, and if I do a check in the hole, I would expect it not to say I'm in a polygon.

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Can you send me your data?

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I figured it out, my points were not correct. If you do the counterclockwise for the hole and clockwise for everything else, that works perfectly.

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