surface area of polygon

CesiumJS
1

Hi,

I need to calculate the surface area of Polygon in Cesium in 3D.

Any help is appreciated!
Thanks.

2

Hello,

Cesium currently doesn’t have this functionality, but we plan on implementing it in the future.

Meanwhile, take a look at Turf.js. Their area implementation isn’t 100% accurate, but it give a close approximation.

Best Regards,

-Hannah

3

Thanks Hannah for the help .
Will look into this.

4

Hey All,

I just worked on this myself and used the following. (It’s rough, but gives a pretty good approximation.)

// Get the polygon from your “entity”
var polygon = theEntity.polygon;

var hierarchy = polygon.hierarchy._value;

// “indices” here defines an array, elements of which defines the indice of a vector

// defining one corner of a triangle. Add up the areas of those triangles to get
// an approximate area for the polygon

var indices = Cesium.PolygonPipeline.triangulate(hierarchy.positions, hierarchy.holes);

var area = 0; // In square kilometers

for (var i = 0; i < indices.length; i += 3) {

var vector1 = hierarchy.positions[indices[i]];

var vector2 = hierarchy.positions[indices[i+1]];

var vector3 = hierarchy.positions[indices[i+2]];

// These vectors define the sides of a parallelogram (double the size of the triangle)

var vectorC = Cesium.Cartesian3.subtract(vector2, vector1, new Cesium.Cartesian3());

var vectorD = Cesium.Cartesian3.subtract(vector3, vector1, new Cesium.Cartesian3());

// Area of parallelogram is the cross product of the vectors defining its sides

var areaVector = Cesium.Cartesian3.cross(vectorC, vectorD, new Cesium.Cartesian3());

// Area of the triangle is just half the area of the parallelogram, add it to the sum.

area += Cesium.Cartesian3.magnitude(areaVector)/2.0;

}

``

Hope that helps.

  • Dave
5

Hi Dave!

Thanks for your code, I just tried but I can't make it work. Is that possible for you send a working example?

BR
Abel