function createWorkingFrustum(camera) {
  const { frustum } = camera;
  if (defined(frustum.fov)) {
    return frustum.clone(scratchPerspectiveFrustum);
  }
  if (defined(frustum.infiniteProjectionMatrix)) {
    return frustum.clone(scratchPerspectiveOffCenterFrustum);
  }
  if (defined(frustum.width)) {
    return frustum.clone(scratchOrthographicFrustum);
  }
  return frustum.clone(scratchOrthographicOffCenterFrustum);
}
Create a working frustum from the original camera frustum.

@param {Camera} camera The camera
@returns {PerspectiveFrustum|PerspectiveOffCenterFrustum|OrthographicFrustum|OrthographicOffCenterFrustum} The working frustum

@private