5

Relative Coordinates
To better understand the concept of relative coordinates, think of a system of satellites,
like the earth, the moon, and the sun. The moon’s parent is the earth, and the earth’s
parent is the sun. Usually, when considering these three bodies, the moon’s position is
described in terms of its position relative to the earth (the moon’s parent), and the earth’s
position is described relative to the sun (the earth’s parent). In Motion, an object’s position
and orientation are always relative to its parent.
When you add a 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 inside other
groups in the Layers list), the parent is the project itself. An object placed inside a group
has its position described relative to its parent: the group.
Group position
set to 100,100,100
In the example above, a group is positioned at X, Y, and Z coordinates of 100, 100, and
100, respectively. The group is located 100 pixels 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 100, 100, 100.
1237Chapter 21 3D Compositing