Sketcher

The sketcher is a central part of the way OpenCAD defines geometry.

Software Design

 * constraint driven
 * parallel
 * perpendicular
 * identical points
 * concentric
 * equal length
 * equal radius
 * tangent
 * symmetry
 * basic entities (first to be implemented)
 * point
 * line
 * arc
 * circle
 * centerline
 * construction line