Point/Curve/Plane

This constraint forces two points to be coincident, or a point to lie on a curve, or a point to lie on a plane.

The point-coincident constraint is available in both 3d and projected versions. The 3d point-coincident constraint restricts three degrees of freedom; the projected version restricts only two. If two points are drawn in a workplane, and then constrained coincident in 3d, then an error will result–they are already coincident in one dimension (the dimension normal to the plane), so the third constraint equation is redundant.

When a point is constrained to lie on a circle (or an arc of a circle), the actual constraint forces the point to lie on the cylindrical surface through that circle. If the point and the circle are already coplanar (e.g., if they are both drawn in the same workplane), then the point will lie on the curve, but otherwise it will not.