More digitizing tool enhancements

[tone90999@…]

I have used JOSM for months, and I feel that digitizing in JOSM is far from satisfactory.

1. Lack of tools to draw lines or points along a constant angle and/or bearing. Sometimes we need to map a feature whose bearing or angle is known (for example, a road which stretches along 45 degrees NE exactly, or a path which is 15 degrees east from the main road). Given that satellite images are always with biases, constructing such a line with mathematically exact data is necessary.
2. Cannot offset lines with arbitrary distance to the original line, only with 0.5m/1.0m/1.5m etc.
3. Unable to generate central lines for rivers or streams.
4. Measurement tool cannot snap to points or line segments, and cannot determine if the length is geodesic or Cartesian.
5. Cannot define coordinate system based on WKT.
6. Sometimes when I move point to a manually input position, it will automatically "shift" for a millimetre or more, which cannot be explained by floating point precision issues.