How to get the coordinates of vertex of a geometry after rotated?

CesiumJS
1

I am trying to calculate the coordinates of each vertex of a polygon. I use Cesium.Transforms.headingPitchRollToFixedFrame() to make the transform matrix and Cesium.Matrix4.multiplyByPoint() to compute the new coordinates.

The following is my code:

var viewer = new Cesium.Viewer(‘cesiumContainer’);

var entities = viewer.entities;

var center = Cesium.Cartesian3.fromDegrees(10, 0);

var heading = Cesium.Math.toRadians(0);

var pitch = Cesium.Math.toRadians(0);

var roll = Cesium.Math.toRadians(0);

var transform = Cesium.Transforms.headingPitchRollToFixedFrame(center, heading, pitch, roll);

entities.add({

polygon: {

hierarchy: new Cesium.PolygonHierarchy(Cesium.Cartesian3.fromDegreesArray([0, 0,

10, 0,

0, 10]))

}

});

var p1 = new Cesium.Cartesian3.fromDegrees(0, 0);

var result1 = Cesium.Matrix4.multiplyByPoint(transform, p1, new Cesium.Cartesian3());

var a1 = Cesium.Ellipsoid.WGS84.cartesianToCartographic(result1);

var p2 = new Cesium.Cartesian3.fromDegrees(10,0);

var result2 = Cesium.Matrix4.multiplyByPoint(transform, p2, new Cesium.Cartesian3());

var a2 = Cesium.Ellipsoid.WGS84.cartesianToCartographic(result2);

var p3 = new Cesium.Cartesian3.fromDegrees(0,10);

var result3 = Cesium.Matrix4.multiplyByPoint(transform, p3, new Cesium.Cartesian3());

var a3 = Cesium.Ellipsoid.WGS84.cartesianToCartographic(result3);

entities.add({

polygon: {

hierarchy: new Cesium.PolygonHierarchy(Cesium.Cartesian3.fromDegreesArray([

Cesium.Math.toDegrees(a1.longitude), Cesium.Math.toDegrees(a1.latitude),

Cesium.Math.toDegrees(a2.longitude), Cesium.Math.toDegrees(a2.latitude),

Cesium.Math.toDegrees(a3.longitude), Cesium.Math.toDegrees(a3.latitude)]))

}

});

viewer.zoomTo(viewer.entities);

But the result shows that the two polygons have distance between and mirror each other even without any rotation…

2

Hello,

I’m not really sure what you are trying to accomplish. Can you please give a little more detail? Like why are you using a transform?

Best,

Hannah

3

Hi Hannah,

Thank you for thr reply.

I was trying to use a transformation matrix to cumput the new coordinats after rotating one vertex based on a specific heading, pitch and roll. So I use the transform fuction to make this matrix. But it seems not right.

If I want to comput the coordinats of vertexes of a rotated polygone based on heading, pitch and roll, how to make the transformation matrix? Or any other function can do it.

Many thanks,
Wei

4

Or I can use entity.orination to rotate polygone, but how to get the rotated coordinates of the polygon from entity.