code: public void setFrustum(float fovy, float aspect, float znear, float zfar)
      {
          Matrix4f projMatrix = new Matrix4f();
          projMatrix.perspective((float) Math.toRadians(fovy), aspect, znear, zfar);
          setFrustum(projMatrix);
      }
docs: Set the view frustum to pick against from the field of view, aspect
  ratio and near, far clip planes. The viewpoint of the frustum
  is the center of the scene object the picker is attached to.
  The view direction is the forward direction of that scene object.
  The frustum will pick what a camera attached to the scene object
  with that view frustum would see. If the frustum is not attached
  to a scene object, it defaults to the view frustum of the main camera of the scene.
  
  @param fovy  vertical field of view in degrees
  @param aspect aspect ratio (width / height)