The symmetric constraint seems to overlook nearly all redundant constraints. At applying a symmetric constraint to certain cases it is possible to produce a sketch with a lot of redundant constraints. First there is no problem. Sometimes a line freezes and is not movable even with reported several degrees of freedom. In other cases those hidden redundant constraints are suddenly detected at changing things at non related objects.

Here is an example of a frozen sketch:

*Frozen sketch with symmetric constraint* - frozen_sketch.png (70.95 KiB) Viewed 3169 times

Sometimes I could move the object, but it jumps. The reported degree of freedom changes between 4 and 5.

An symmetric constraint was applied between the endpoints of the arc and the horizontal line. After adding the vertical line, the sketch became unmovable.

Hidden redundant constraints are easy constructed with applying a symmetric constraint to:

Two lines with parallel constraint.

Two lines with equality constraint.

Two lines with perpendicular constraint.

Endpoint of arcs with symmetry to a line through the center of the arc.

There may be also other cases.

Ulrich

OS: Debian GNU/Linux 7.5 (wheezy)

Platform: 32-bit

Version: 0.14.3609 (Git)

Branch: master

Hash: 052b628cbf02624f53e5b844e0c92083b83d368e

Python version: 2.7.3

Qt version: 4.8.2

Coin version: 3.1.3

SoQt version: 1.5.0

OCC version: 6.7.0