(camera-prop { geometry object } [projective])Specify the object to be shown when drawing other cameras.
By default, this object is drawn with its origin at the camera,
and with the camera looking toward the object’s -Z axis.
With the projective keyword, the camera’s viewing projection is
also applied to the object; this places the object’s Z=-1 and Z=+1 at
near and far clipping planes, with the viewing area -1<={X,Y}<=+1.
Example: (camera-prop { < cube } projective)