let position = new THREE.Vector3();
position.applyMatrix4(transform)

// Get the position from the current transform matrix.
  let position = new THREE.Vector3();
  position.setFromMatrixPosition(transform);   <===== A

  // Create a matrix to do rotation of -90 degrees on the z axis.
  let rotateTransform = new THREE.Matrix4();
  rotateTransform.makeRotationFromEuler(new THREE.Euler(0, 0, MyHelper.ConvertToRadian(-90)));

  // Apply the rotation
  transform.multiply(rotateTransform);

  // Get the position again. Should be different result to above
  position.setFromMatrixPosition(transform);  <===== B

  // Try a different approach
  let transform3 = new THREE.Matrix4();
  let quat2 = new THREE.Quaternion();
  quat2.setFromEuler(new THREE.Euler(MyHelper.ConvertToRadian(-90),0 , 0));
        transform3.compose(new THREE.Vector3(0,0,0), quat2, new THREE.Vector3(0,0,0));
  transform.multiply(transform3);
  absPos.setFromMatrixPosition(transform);  <====== C