Primitive.prototype.convexHull does not support GeometryCollection

[jgravois]

from Esri/terraformer#313

I have geojson geometries that include GeometryCollections. The current implementation of convexHull in terraformer does not support "GeometryCollection" in convexHull.

I have made my own code that fixes convexHull. I'm attaching my code but it is in typescript.
You can use it as reference or easily addapt it to javascript.

Hopefully you can get this fixed in a future release.

public convexHull(): Polygon | null {
    function getCoordinates(shape: any) {
        let coordinates = [] as any;
        let i;
        let j;
        if (shape.type === 'Point') {
            if (shape.coordinates) {
                const returnArray = [];
                returnArray.push(shape.coordinates)
                return returnArray;
            } else {
                return null
            }
        } else if (shape.type === 'LineString' || shape.type === 'MultiPoint') {
            if (shape.coordinates) {
                return shape.coordinates;
            } else {
                return null;
            }
        } else if (shape.type === 'Polygon' || shape.type === 'MultiLineString') {
            if (shape.coordinates) {
                for (i = 0; i < shape.coordinates.length; i++) {
                    coordinates = coordinates.concat(shape.coordinates[i]);
                }
                if (coordinates) {
                    return coordinates;
                } else {
                    return null;
                }
            } else {
                return null;
            }
        } else if (shape.type === 'MultiPolygon') {
            if (shape.coordinates && shape.coordinates.length > 0) {
                for (i = 0; i < shape.coordinates.length; i++) {
                    for (j = 0; j < shape.coordinates[i].length; j++) {
                        coordinates = coordinates.concat(shape.coordinates[i][j]);
                    }
                }
                if (coordinates) {
                    return coordinates;
                } else {
                    return null;
                }
            } else {
                return null;
            }
        } else if (shape.type === 'GeometryCollection') {
            for (const index in shape.geometries) {
                if (index) {
                    const delta = getCoordinates(shape.geometries[index]);
                    if (delta) {
                        coordinates = coordinates.concat(delta);
                    } else {
                        return null;
                    }
                }
            }
            return coordinates;
        }
    }

    function pointsEqual(a: any, b: any) {
        for (let bb = 0; bb < a.length; bb++) {
            if (a[bb] !== b[bb]) {
                return false;
            }
        }
        return true;
    }

    function closedPolygon(coordinates2: any) {
        const outer = [];
        for (const coordinate of coordinates2) {
            const inner = coordinate.slice();
            if (pointsEqual(inner[0], inner[inner.length - 1]) === false) {
                inner.push(inner[0]);
            }
            outer.push(inner);
        }
        return outer;
    }

    let cords;
    if (this.type === "Feature") {
        cords = getCoordinates((this as any).geometry);
    } else {
        cords = getCoordinates(this);
    }

    if (cords && cords.length >= 3) {
        return new Terraformer.Polygon({
            coordinates: closedPolygon([Terraformer.Tools.convexHull(cords)]),
            type: 'Polygon'
        });
    } else {
        console.log("Invalid geometry. At least 3 coordinates are required to generate a convex hull.")
        return null
    }
}