92 lines
No EOL
2.4 KiB
JavaScript
92 lines
No EOL
2.4 KiB
JavaScript
var geometryArea = geometry;
|
|
|
|
turf_area = function(_) {
|
|
if (_.type === 'FeatureCollection') {
|
|
for (var i = 0, sum = 0; i < _.features.length; i++) {
|
|
if (_.features[i].geometry) {
|
|
sum += geometryArea(_.features[i].geometry);
|
|
}
|
|
}
|
|
return sum;
|
|
} else if (_.type === 'Feature') {
|
|
return geometryArea(_.geometry);
|
|
} else {
|
|
return geometryArea(_);
|
|
}
|
|
};
|
|
|
|
RADIUS = 6378137;
|
|
FLATTENING = 1/298.257223563;
|
|
POLAR_RADIUS = 6356752.3142;
|
|
|
|
ring = ringArea;
|
|
|
|
function geometry(_) {
|
|
var area = 0, i;
|
|
switch (_.type) {
|
|
case 'Polygon':
|
|
return polygonArea(_.coordinates);
|
|
case 'MultiPolygon':
|
|
for (i = 0; i < _.coordinates.length; i++) {
|
|
area += polygonArea(_.coordinates[i]);
|
|
}
|
|
return area;
|
|
case 'Point':
|
|
case 'MultiPoint':
|
|
case 'LineString':
|
|
case 'MultiLineString':
|
|
return 0;
|
|
case 'GeometryCollection':
|
|
for (i = 0; i < _.geometries.length; i++) {
|
|
area += geometry(_.geometries[i]);
|
|
}
|
|
return area;
|
|
}
|
|
}
|
|
|
|
function polygonArea(coords) {
|
|
var area = 0;
|
|
if (coords && coords.length > 0) {
|
|
area += Math.abs(ringArea(coords[0]));
|
|
for (var i = 1; i < coords.length; i++) {
|
|
area -= Math.abs(ringArea(coords[i]));
|
|
}
|
|
}
|
|
return area;
|
|
}
|
|
|
|
function ringArea(coords) {
|
|
var p1, p2, p3, lowerIndex, middleIndex, upperIndex,
|
|
area = 0,
|
|
coordsLength = coords.length;
|
|
|
|
if (coordsLength > 2) {
|
|
for (i = 0; i < coordsLength; i++) {
|
|
if (i === coordsLength - 2) {// i = N-2
|
|
lowerIndex = coordsLength - 2;
|
|
middleIndex = coordsLength -1;
|
|
upperIndex = 0;
|
|
} else if (i === coordsLength - 1) {// i = N-1
|
|
lowerIndex = coordsLength - 1;
|
|
middleIndex = 0;
|
|
upperIndex = 1;
|
|
} else { // i = 0 to N-3
|
|
lowerIndex = i;
|
|
middleIndex = i+1;
|
|
upperIndex = i+2;
|
|
}
|
|
p1 = coords[lowerIndex];
|
|
p2 = coords[middleIndex];
|
|
p3 = coords[upperIndex];
|
|
area += ( rad(p3[0]) - rad(p1[0]) ) * Math.sin( rad(p2[1]));
|
|
}
|
|
|
|
area = area * RADIUS * RADIUS / 2;
|
|
}
|
|
|
|
return area;
|
|
}
|
|
|
|
function rad(_) {
|
|
return _ * Math.PI / 180;
|
|
} |