How to get the outline of a group of polygons, without holes ?

[Dylan190774]

I have several polygons of country-shapes.
I want to get the outline of a group of countries.

For example: Switzerland and Austria.
The problem is that there is Liechtenstein inbetween those countries.

I know I can use unify, but if I don't include Liechtenstein, there's a hole (empty space) in the outline-polygon.

Is there any way to get the entire outline of a group of polygons, even if there is a hole?

[alexbol99]

Hi, @Dylan190774 ,

If I understood correctly, after unify you want to filter holes.
You can do it this way, because all the holes has orientation opposite to exterior face:

function filterHoles(poly) {
    const orientation = [...poly.faces][0].orientation();
    const newPoly = new Polygon()
    for (let face of poly.faces) {
        if (face.orientation() === orientation) {
            newPoly.addFace(face.shapes);
        }
    }
    return newPoly;
}