Apple Motion 4 - Manual (Page 1194)

When you add a new group to a Motion project, that group is created at the origin
coordinates of its parent. In the case of a root-level group (a group that is not nested within
any other groups in the Layers tab), the parent is the project itself. An object placed inside
of a group has its position described relative to its parent: the group.
Group at X=50, Y=50, Z=50 Group Inspector
In the previous example, a group has been positioned at X, Y, and Z coordinates of 50,
50, and 50, respectively. The group is located 50 units away from its parent’s origin on all
axes (the parent in this case being the project itself ). The image inside the group is
positioned at 0, 0, 0. Because the image’s position is relative to its parent, the group, it
shares its parent’s origin and has an apparent position in the world of 50, 50, 50.
Moving the image to a position of 25, 25, 25 displaces it by 25 units from the group’s
origin in all axes. While the image’s apparent position relative to the world is 75, 75, 75,
its Position values in the Inspector are 25, 25, 25 because its position is always relative to
its parent.
Image in group at 25, 25, 25 Image Inspector
1194 Chapter 18 3D Compositing