Tracing button in the snapping toolbar gets extra menu where it is possible to set
offset that will be applied to the traced line. Offset value can be either positive
(right side) or negative (left side).
Because
- OTF reprojection is mature and stable
- Should be no cost when not required - transforms are shortcut
when not required
- Reduces code complexity
- Canvas OTF support was being incorrectly used as a flag for
whether measurements should be made in ellipsoidal mode. Instead
the project's ellipsoid setting should be checked for this.
- Should simplify behavior for new users
