| 1 | function rad(x) {
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| 2 | return x * Math.PI / 180;
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| 3 | }
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| 4 |
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| 5 | function isRingClockwise (coords) {
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| 6 | var area = 0;
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| 7 | if (coords.length > 2) {
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| 8 | var p1, p2;
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| 9 | for (var i = 0; i < coords.length - 1; i++) {
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| 10 | p1 = coords[i];
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| 11 | p2 = coords[i + 1];
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| 12 | area += rad(p2[0] - p1[0]) * (2 + Math.sin(rad(p1[1])) + Math.sin(rad(p2[1])));
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| 13 | }
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| 14 | }
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| 15 |
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| 16 | return area >= 0;
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| 17 | }
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| 18 |
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| 19 | function isPolyRHR (coords) {
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| 20 | if (coords && coords.length > 0) {
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| 21 | if (isRingClockwise(coords[0]))
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| 22 | return false;
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| 23 | var interiorCoords = coords.slice(1, coords.length);
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| 24 | if (!interiorCoords.every(isRingClockwise))
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| 25 | return false;
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| 26 | }
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| 27 | return true;
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| 28 | }
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| 29 |
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| 30 | function rightHandRule (geometry) {
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| 31 | if (geometry.type === 'Polygon') {
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| 32 | return isPolyRHR(geometry.coordinates);
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| 33 | } else if (geometry.type === 'MultiPolygon') {
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| 34 | return geometry.coordinates.every(isPolyRHR);
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| 35 | }
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| 36 | }
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| 37 |
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| 38 | module.exports = function validateRightHandRule(geometry, errors) {
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| 39 | if (!rightHandRule(geometry)) {
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| 40 | errors.push({
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| 41 | message: 'Polygons and MultiPolygons should follow the right-hand rule',
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| 42 | level: 'message',
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| 43 | line: geometry.__line__
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| 44 | });
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| 45 | }
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| 46 | };
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