packages/geojson-utils/geojson-utils.js
(function () {
var gju = {};
// Export the geojson object for **CommonJS**
if (typeof module !== 'undefined' && module.exports) {
module.exports = gju;
}
// adapted from http://www.kevlindev.com/gui/math/intersection/Intersection.js
gju.lineStringsIntersect = function (l1, l2) {
var intersects = [];
for (var i = 0; i <= l1.coordinates.length - 2; ++i) {
for (var j = 0; j <= l2.coordinates.length - 2; ++j) {
var a1 = {
x: l1.coordinates[i][1],
y: l1.coordinates[i][0]
},
a2 = {
x: l1.coordinates[i + 1][1],
y: l1.coordinates[i + 1][0]
},
b1 = {
x: l2.coordinates[j][1],
y: l2.coordinates[j][0]
},
b2 = {
x: l2.coordinates[j + 1][1],
y: l2.coordinates[j + 1][0]
},
ua_t = (b2.x - b1.x) * (a1.y - b1.y) - (b2.y - b1.y) * (a1.x - b1.x),
ub_t = (a2.x - a1.x) * (a1.y - b1.y) - (a2.y - a1.y) * (a1.x - b1.x),
u_b = (b2.y - b1.y) * (a2.x - a1.x) - (b2.x - b1.x) * (a2.y - a1.y);
if (u_b != 0) {
var ua = ua_t / u_b,
ub = ub_t / u_b;
if (0 <= ua && ua <= 1 && 0 <= ub && ub <= 1) {
intersects.push({
'type': 'Point',
'coordinates': [a1.x + ua * (a2.x - a1.x), a1.y + ua * (a2.y - a1.y)]
});
}
}
}
}
if (intersects.length == 0) intersects = false;
return intersects;
}
// Bounding Box
function boundingBoxAroundPolyCoords (coords) {
var xAll = [], yAll = []
for (var i = 0; i < coords[0].length; i++) {
xAll.push(coords[0][i][1])
yAll.push(coords[0][i][0])
}
xAll = xAll.sort(function (a,b) { return a - b })
yAll = yAll.sort(function (a,b) { return a - b })
return [ [xAll[0], yAll[0]], [xAll[xAll.length - 1], yAll[yAll.length - 1]] ]
}
gju.pointInBoundingBox = function (point, bounds) {
return !(point.coordinates[1] < bounds[0][0] || point.coordinates[1] > bounds[1][0] || point.coordinates[0] < bounds[0][1] || point.coordinates[0] > bounds[1][1])
}
// Point in Polygon
// http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html#Listing the Vertices
function pnpoly (x,y,coords) {
var vert = [ [0,0] ]
for (var i = 0; i < coords.length; i++) {
for (var j = 0; j < coords[i].length; j++) {
vert.push(coords[i][j])
}
vert.push([0,0])
}
var inside = false
for (var i = 0, j = vert.length - 1; i < vert.length; j = i++) {
if (((vert[i][0] > y) != (vert[j][0] > y)) && (x < (vert[j][1] - vert[i][1]) * (y - vert[i][0]) / (vert[j][0] - vert[i][0]) + vert[i][1])) inside = !inside
}
return inside
}
gju.pointInPolygon = function (p, poly) {
var coords = (poly.type == "Polygon") ? [ poly.coordinates ] : poly.coordinates
var insideBox = false
for (var i = 0; i < coords.length; i++) {
if (gju.pointInBoundingBox(p, boundingBoxAroundPolyCoords(coords[i]))) insideBox = true
}
if (!insideBox) return false
var insidePoly = false
for (var i = 0; i < coords.length; i++) {
if (pnpoly(p.coordinates[1], p.coordinates[0], coords[i])) insidePoly = true
}
return insidePoly
}
gju.numberToRadius = function (number) {
return number * Math.PI / 180;
}
gju.numberToDegree = function (number) {
return number * 180 / Math.PI;
}
// written with help from @tautologe
gju.drawCircle = function (radiusInMeters, centerPoint, steps) {
var center = [centerPoint.coordinates[1], centerPoint.coordinates[0]],
dist = (radiusInMeters / 1000) / 6371,
// convert meters to radiant
radCenter = [gju.numberToRadius(center[0]), gju.numberToRadius(center[1])],
steps = steps || 15,
// 15 sided circle
poly = [[center[0], center[1]]];
for (var i = 0; i < steps; i++) {
var brng = 2 * Math.PI * i / steps;
var lat = Math.asin(Math.sin(radCenter[0]) * Math.cos(dist)
+ Math.cos(radCenter[0]) * Math.sin(dist) * Math.cos(brng));
var lng = radCenter[1] + Math.atan2(Math.sin(brng) * Math.sin(dist) * Math.cos(radCenter[0]),
Math.cos(dist) - Math.sin(radCenter[0]) * Math.sin(lat));
poly[i] = [];
poly[i][1] = gju.numberToDegree(lat);
poly[i][0] = gju.numberToDegree(lng);
}
return {
"type": "Polygon",
"coordinates": [poly]
};
}
// assumes rectangle starts at lower left point
gju.rectangleCentroid = function (rectangle) {
var bbox = rectangle.coordinates[0];
var xmin = bbox[0][0],
ymin = bbox[0][1],
xmax = bbox[2][0],
ymax = bbox[2][1];
var xwidth = xmax - xmin;
var ywidth = ymax - ymin;
return {
'type': 'Point',
'coordinates': [xmin + xwidth / 2, ymin + ywidth / 2]
};
}
// from http://www.movable-type.co.uk/scripts/latlong.html
gju.pointDistance = function (pt1, pt2) {
var lon1 = pt1.coordinates[0],
lat1 = pt1.coordinates[1],
lon2 = pt2.coordinates[0],
lat2 = pt2.coordinates[1],
dLat = gju.numberToRadius(lat2 - lat1),
dLon = gju.numberToRadius(lon2 - lon1),
a = Math.pow(Math.sin(dLat / 2), 2) + Math.cos(gju.numberToRadius(lat1))
* Math.cos(gju.numberToRadius(lat2)) * Math.pow(Math.sin(dLon / 2), 2),
c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
// Earth radius is 6371 km
return (6371 * c) * 1000; // returns meters
},
// checks if geometry lies entirely within a circle
// works with Point, LineString, Polygon
gju.geometryWithinRadius = function (geometry, center, radius) {
if (geometry.type == 'Point') {
return gju.pointDistance(geometry, center) <= radius;
} else if (geometry.type == 'LineString' || geometry.type == 'Polygon') {
var point = {};
var coordinates;
if (geometry.type == 'Polygon') {
// it's enough to check the exterior ring of the Polygon
coordinates = geometry.coordinates[0];
} else {
coordinates = geometry.coordinates;
}
for (var i in coordinates) {
point.coordinates = coordinates[i];
if (gju.pointDistance(point, center) > radius) {
return false;
}
}
}
return true;
}
// adapted from http://paulbourke.net/geometry/polyarea/javascript.txt
gju.area = function (polygon) {
var area = 0;
// TODO: polygon holes at coordinates[1]
var points = polygon.coordinates[0];
var j = points.length - 1;
var p1, p2;
for (var i = 0; i < points.length; j = i++) {
var p1 = {
x: points[i][1],
y: points[i][0]
};
var p2 = {
x: points[j][1],
y: points[j][0]
};
area += p1.x * p2.y;
area -= p1.y * p2.x;
}
area /= 2;
return area;
},
// adapted from http://paulbourke.net/geometry/polyarea/javascript.txt
gju.centroid = function (polygon) {
var f, x = 0,
y = 0;
// TODO: polygon holes at coordinates[1]
var points = polygon.coordinates[0];
var j = points.length - 1;
var p1, p2;
for (var i = 0; i < points.length; j = i++) {
var p1 = {
x: points[i][1],
y: points[i][0]
};
var p2 = {
x: points[j][1],
y: points[j][0]
};
f = p1.x * p2.y - p2.x * p1.y;
x += (p1.x + p2.x) * f;
y += (p1.y + p2.y) * f;
}
f = gju.area(polygon) * 6;
return {
'type': 'Point',
'coordinates': [y / f, x / f]
};
},
gju.simplify = function (source, kink) { /* source[] array of geojson points */
/* kink in metres, kinks above this depth kept */
/* kink depth is the height of the triangle abc where a-b and b-c are two consecutive line segments */
kink = kink || 20;
source = source.map(function (o) {
return {
lng: o.coordinates[0],
lat: o.coordinates[1]
}
});
var n_source, n_stack, n_dest, start, end, i, sig;
var dev_sqr, max_dev_sqr, band_sqr;
var x12, y12, d12, x13, y13, d13, x23, y23, d23;
var F = (Math.PI / 180.0) * 0.5;
var index = new Array(); /* aray of indexes of source points to include in the reduced line */
var sig_start = new Array(); /* indices of start & end of working section */
var sig_end = new Array();
/* check for simple cases */
if (source.length < 3) return (source); /* one or two points */
/* more complex case. initialize stack */
n_source = source.length;
band_sqr = kink * 360.0 / (2.0 * Math.PI * 6378137.0); /* Now in degrees */
band_sqr *= band_sqr;
n_dest = 0;
sig_start[0] = 0;
sig_end[0] = n_source - 1;
n_stack = 1;
/* while the stack is not empty ... */
while (n_stack > 0) {
/* ... pop the top-most entries off the stacks */
start = sig_start[n_stack - 1];
end = sig_end[n_stack - 1];
n_stack--;
if ((end - start) > 1) { /* any intermediate points ? */
/* ... yes, so find most deviant intermediate point to
either side of line joining start & end points */
x12 = (source[end].lng() - source[start].lng());
y12 = (source[end].lat() - source[start].lat());
if (Math.abs(x12) > 180.0) x12 = 360.0 - Math.abs(x12);
x12 *= Math.cos(F * (source[end].lat() + source[start].lat())); /* use avg lat to reduce lng */
d12 = (x12 * x12) + (y12 * y12);
for (i = start + 1, sig = start, max_dev_sqr = -1.0; i < end; i++) {
x13 = source[i].lng() - source[start].lng();
y13 = source[i].lat() - source[start].lat();
if (Math.abs(x13) > 180.0) x13 = 360.0 - Math.abs(x13);
x13 *= Math.cos(F * (source[i].lat() + source[start].lat()));
d13 = (x13 * x13) + (y13 * y13);
x23 = source[i].lng() - source[end].lng();
y23 = source[i].lat() - source[end].lat();
if (Math.abs(x23) > 180.0) x23 = 360.0 - Math.abs(x23);
x23 *= Math.cos(F * (source[i].lat() + source[end].lat()));
d23 = (x23 * x23) + (y23 * y23);
if (d13 >= (d12 + d23)) dev_sqr = d23;
else if (d23 >= (d12 + d13)) dev_sqr = d13;
else dev_sqr = (x13 * y12 - y13 * x12) * (x13 * y12 - y13 * x12) / d12; // solve triangle
if (dev_sqr > max_dev_sqr) {
sig = i;
max_dev_sqr = dev_sqr;
}
}
if (max_dev_sqr < band_sqr) { /* is there a sig. intermediate point ? */
/* ... no, so transfer current start point */
index[n_dest] = start;
n_dest++;
} else { /* ... yes, so push two sub-sections on stack for further processing */
n_stack++;
sig_start[n_stack - 1] = sig;
sig_end[n_stack - 1] = end;
n_stack++;
sig_start[n_stack - 1] = start;
sig_end[n_stack - 1] = sig;
}
} else { /* ... no intermediate points, so transfer current start point */
index[n_dest] = start;
n_dest++;
}
}
/* transfer last point */
index[n_dest] = n_source - 1;
n_dest++;
/* make return array */
var r = new Array();
for (var i = 0; i < n_dest; i++)
r.push(source[index[i]]);
return r.map(function (o) {
return {
type: "Point",
coordinates: [o.lng, o.lat]
}
});
}
// http://www.movable-type.co.uk/scripts/latlong.html#destPoint
gju.destinationPoint = function (pt, brng, dist) {
dist = dist/6371; // convert dist to angular distance in radians
brng = gju.numberToRadius(brng);
var lat1 = gju.numberToRadius(pt.coordinates[0]);
var lon1 = gju.numberToRadius(pt.coordinates[1]);
var lat2 = Math.asin( Math.sin(lat1)*Math.cos(dist) +
Math.cos(lat1)*Math.sin(dist)*Math.cos(brng) );
var lon2 = lon1 + Math.atan2(Math.sin(brng)*Math.sin(dist)*Math.cos(lat1),
Math.cos(dist)-Math.sin(lat1)*Math.sin(lat2));
lon2 = (lon2+3*Math.PI) % (2*Math.PI) - Math.PI; // normalise to -180..+180ยบ
return {
'type': 'Point',
'coordinates': [gju.numberToDegree(lat2), gju.numberToDegree(lon2)]
};
};
})();