How to use martinez-polygon-clipping - 10 common examples

const simple_intersect = function (A_Vs2d, B_Vs2d) {
  // find 2d intersection of two polygons each specified as list of 2d vertices.
  try {
    // martinez lib expects geojson multi-path polygon which uses repeated final vertices.
    const A_Vs2d_ = A_Vs2d.concat([A_Vs2d[0]]);
    const B_Vs2d_ = B_Vs2d.concat([B_Vs2d[0]]);
    const result = martinez.intersection([A_Vs2d_], [B_Vs2d_]);
    // assume simple intersection structure
    // take 1st polygon, 1st path, drop last repeated vertex
    if (result.length > 0 && result[0].length > 0) {
      return result[0][0].slice(0, result[0][0].length);
    } else {
      return [];
    }
  } catch (e) { // catch rare errors
    console.log(e);
    return [];
  }
}

Offset.prototype.offsetContour = function(curve, edges) {
  var union, i, len;
  if (isArray(curve[0]) && typeof curve[0][0] === 'number') {
    // we have 1 less edge than vertices
    for (i = 0, len = curve.length - 1; i < len; i++) {
      var segment = this.ensureLastPoint(
        this._offsetSegment(curve[i], curve[i + 1], edges[i], this._distance)
      );
      union = (i === 0) ?
                [this.ensureLastPoint(segment)] :
                martinez.union(union, this.ensureLastPoint(segment));
    }
  } else {
    for (i = 0, len = edges.length; i < len; i++) {
      union = (i === 0) ?
        this.offsetContour(curve[i], edges[i]) :
        martinez.union(union, this.offsetContour(curve[i], edges[i]));
    }
  }
  return union;
};

var union, i, len;
  if (isArray(curve[0]) && typeof curve[0][0] === 'number') {
    // we have 1 less edge than vertices
    for (i = 0, len = curve.length - 1; i < len; i++) {
      var segment = this.ensureLastPoint(
        this._offsetSegment(curve[i], curve[i + 1], edges[i], this._distance)
      );
      union = (i === 0) ?
                [this.ensureLastPoint(segment)] :
                martinez.union(union, this.ensureLastPoint(segment));
    }
  } else {
    for (i = 0, len = edges.length; i < len; i++) {
      union = (i === 0) ?
        this.offsetContour(curve[i], edges[i]) :
        martinez.union(union, this.offsetContour(curve[i], edges[i]));
    }
  }
  return union;
};

Offset.prototype.offsetContour = function(curve, edges) {
  var union, i, len;
  if (isArray(curve[0]) && typeof curve[0][0] === 'number') {
    // we have 1 less edge than vertices
    for (i = 0, len = curve.length - 1; i < len; i++) {
      var segment = this.ensureLastPoint(
        this._offsetSegment(curve[i], curve[i + 1], edges[i], this._distance)
      );
      union = (i === 0) ?
                [this.ensureLastPoint(segment)] :
                martinez.union(union, this.ensureLastPoint(segment));
    }
  } else {
    for (i = 0, len = edges.length; i < len; i++) {
      union = (i === 0) ?
        this.offsetContour(curve[i], edges[i]) :
        martinez.union(union, this.offsetContour(curve[i], edges[i]));
    }
  }
  return union;
};

var union, i, len;
  if (isArray(curve[0]) && typeof curve[0][0] === 'number') {
    // we have 1 less edge than vertices
    for (i = 0, len = curve.length - 1; i < len; i++) {
      var segment = this.ensureLastPoint(
        this._offsetSegment(curve[i], curve[i + 1], edges[i], this._distance)
      );
      union = (i === 0) ?
                [this.ensureLastPoint(segment)] :
                martinez.union(union, this.ensureLastPoint(segment));
    }
  } else {
    for (i = 0, len = edges.length; i < len; i++) {
      union = (i === 0) ?
        this.offsetContour(curve[i], edges[i]) :
        martinez.union(union, this.offsetContour(curve[i], edges[i]));
    }
  }
  return union;
};

Offset.prototype.margin = function(dist) {
  this.distance(dist);

  if (typeof this.vertices[0] === 'number') { // point
    return this.offsetPoint(this._distance);
  }

  if (dist === 0) return this.vertices;

  var union = this.offsetLines(this._distance);
  //return union;
  union = martinez.union(this.vertices, union);
  return orientRings(union);
};

Offset.prototype.margin = function(dist) {
  this.distance(dist);

  if (typeof this.vertices[0] === 'number') { // point
    return this.offsetPoint(this._distance);
  }

  if (dist === 0) return this.vertices;

  var union = this.offsetLines(this._distance);
  //return union;
  union = martinez.union(this.vertices, union);
  return orientRings(union);
};

}

                // Generate some unique IDs and add some metadata
                var featurehash = utilHashcode(stringify(feature));
                var propertyhash = utilHashcode(stringify(feature.properties || {}));
                feature.__layerID__ = layerID.replace(/[^_a-zA-Z0-9\-]/g, '_');
                feature.__featurehash__ = featurehash;
                feature.__propertyhash__ = propertyhash;
                features.push(feature);

                // Clipped Polygons at same zoom with identical properties can get merged
                if (isClipped && geometry.type === 'MultiPolygon') {
                    var merged = mergeCache[propertyhash];
                    if (merged && merged.length) {
                        var other = merged[0];
                        var coords = martinez.union(
                            feature.geometry.coordinates, other.geometry.coordinates
                        );

                        if (!coords || !coords.length) {
                            continue;  // something failed in martinez union
                        }

                        merged.push(feature);
                        for (var j = 0; j < merged.length; j++) {      // all these features get...
                            merged[j].geometry.coordinates = coords;   // same coords
                            merged[j].__featurehash__ = featurehash;   // same hash, so deduplication works
                        }
                    } else {
                        mergeCache[propertyhash] = [feature];
                    }
                }

function difference(polygon1, polygon2) {
    var geom1 = getGeom(polygon1);
    var geom2 = getGeom(polygon2);
    var properties = polygon1.properties || {};

    // Issue #721 - JSTS/Martinez can't handle empty polygons
    geom1 = removeEmptyPolygon(geom1);
    geom2 = removeEmptyPolygon(geom2);
    if (!geom1) return null;
    if (!geom2) return feature(geom1, properties);

    var differenced = martinez.diff(geom1.coordinates, geom2.coordinates);
    if (differenced.length === 0) return null;
    if (differenced.length === 1) return polygon(differenced[0], properties);
    else return multiPolygon(differenced, properties);
}

function intersect(poly1, poly2) {
    var geom1 = getGeom(poly1);
    var geom2 = getGeom(poly2);
    var properties = poly1.properties || {};
    // Return null if geometry is too narrow in coordinate precision
    // fixes topology errors with JSTS
    // https://github.com/Turfjs/turf/issues/463
    // https://github.com/Turfjs/turf/pull/1004
    // if (cleanCoords(truncate(geom2, {precision: 4})).coordinates[0].length < 4) return null;
    // if (cleanCoords(truncate(geom1, {precision: 4})).coordinates[0].length < 4) return null;

    var intersection = martinez.intersection(geom1.coordinates, geom2.coordinates);
    if (intersection === null || intersection.length === 0) return null;
    if (intersection.length === 1) return polygon(intersection[0], properties);
    else return multiPolygon(intersection, properties);
}