Description:

Constrain one multi-point surface to be a flat plane at any orientation

Objects:

One multi-point Surface (must have 4 or more 3D Object Points in Surface)

Number allowed:

One constraint per planar Surface

Use:

Since any Surface with 4 or more points is not necessarily planar, this constraint lets you specify this.  This allows you to propagate 3D information along a surface plane when three of the points of the surface are already computable in 3D.  Used mainly in single photo projects. For multi-photo projects and solution during Global Optimization stage see the 4 or more points to be coplanar Constraint.