/*
<subsection>Object Tracking</subsection>

In Blender, Objects can be given a rotation ~constraint so that they
always refer to a "Track" Object.  Activate the option in the 3DWindow
with CTRL+T: "Make Track". All selected Objects now refer to the
~active Object.  Since Objects can also have their own rotation, this
rotation van better be erased first: ALT+R. If the Object is a Child,
erase the "Parent Inverse" also: ALT+P.  Then use the tracking buttons
again to specify the desired tracking effect.
<p>
The tracking ~constraint is the 'odd man out' in the hierarchy. Parent
rotations and the rotation of the Object itself can affect
tracking. The option EditButtons->PowerTrack can be used to ignore the
Object and Parent rotations.
<p>
Tracking is often used with Cameras to make sure that the main subject
is always visible. The disadvantage of tracking is that it occurs
~perfectly. The object being followed always appears in the centre of
the picture, making it appear to stand almost completely still.  Use
of manually inserted Object Ipos in Cameras gives a more natural
effect. Carefully chosen camera positions and subtle camera movements
can have a significant impact on the power of an animation.


<section>Vertex Keys</section>

<subsection>The Key block</subsection>

VertexKeys, which should not be confused with "Object keys", the
specified positions of Objects, can also be created in Blender;
VertexKeys are the specified positions of vertices in ObData. Since
this can involve thousands of vertices, separate motion curves are not
created for each vertex, but the traditional Key position system is
used instead. A single IpoCurve is used to determine how interpolation
is performed and the times at which a VertexKey can be seen.
<p>
VertexKeys are part of ObData, not of an Object. When duplicating
ObData, the associated VertexKey block is also copied. It is not
possible to permit multiple users to use VertexKeys in Blender, since
it would not be very practical.
<p>
The Key block is also universal and understands the distinction
between a Mesh, Curve, Surface or Lattice. Their interface and use are
therefore identical. Working with Mesh VertexKeys is explained in
detail in this section, which also contains a number of brief comments
on the other ObData.
<p>
The first VertexKey position created, is always the ~reference Key.
This key defines the texture coordinates. Only with this Key ~active
the faces and curves or the ~number of vertices can be changed.  It is
allowed to assign other Keys a different number of vertices. The Key
system automatically interpolates this.

*/

