private Mat3 rotateX(float angDeg) {
float angRad = degToRad( angDeg );
float cos = (float) Math.cos( angRad );
float sin = (float) Math.sin( angRad );
Mat3 theMat = new Mat3( 1.0f );
theMat.set( 1, 1, cos );
theMat.set( 2, 1, -sin );
theMat.set( 1, 2, sin );
theMat.set( 2, 2, cos );
return theMat;
}