 # Position been changed when try to rotate primitive

I try to rotate a primitive（The primitive has 1000 rectangles, each with its own location）, but when i use code like this, i find position be changed at same time.how could i do to make it right. can any one help me?（the oldModelMatrix is default modelMatrix）
let matrix3=Matrix3.fromRotationY(Math.toRadians(angle));
let rz = Matrix4.fromRotationTranslation(matrix3);
let result = Matrix4.multiply(oldModelMatrix, rz, oldModelMatrix);

Hi,

Welcome to the community! Could you please share a Sandcastle showing how you’re constructing the primitive and updating its matrix?

Thanks,
Eli

i got a primitve with 1000 rectangle by

let myprimitive = new Primitive({
geometryInstances: [myGeometrys],
appearance: new PerInstanceColorAppearance()
})

and the myGeometrys is an Array of rectangle geometryInstance, like:

let myGeomInstance = new GeometryInstance({
geometry: new RectangleGeometry({
rectangle: Rectangle.fromDegrees(
west,
south,
east,
north
),
}),
attributes: {
color: ColorGeometryInstanceAttribute.fromColor(Color.RED),
},
})

and after added it to Viewer, i try to rotate the primitive by modeMatrix, i use:

let matrix3=Matrix3.fromRotationY(Math.toRadians(angle));
let rz = Matrix4.fromRotationTranslation(matrix3);
let result = Matrix4.multiply(myprimitive.modelMatrix, rz, new Matrix4());

It’s work, but primitive’s position has been changed at same time.Then i try to get center of primitive position to reset the primitive rotate origin point

let center = Transforms.eastNorthUpToFixedFrame(centerPosition);

And primitive fly to another position(have a height that i never set).
I’m confused by the rotation of ModeMatrix. Is there anything I haven’t noticed?