It would be ideal if we can have an additional command such as BillboardGroupLockAxis(GroupID, x, y, z).
If you set 1 for one or more axis PB should lock it and prevent billboards from rotating on that axis.
To justify this request run the BillboardGrass.pb example.
If the camera is moved above the ground billboards will face it and make the grass look unnatural. If we lock both the X and Z axis using the BillboardGroupLockAxis() grass would look more natural and still face the front instead of the top. Using combination of one or more axis-locked billboard groups a more natural environment can be achieved.
Same goes for flat-trees. Once you are above them it would look silly if they face the camera (including the trunks


Please consider. Thanks!