[josm-dev] Geometric calculations and projections

[Matthias Julius]

Some (all?) gemetric calculations in JOSM like the intersectin point of
two way segments use the current map projection as basis. I don't think
it should be like that. I feel somewhat uneasy when the result of some
action depends on some user settings. In extreme cases this can even
result in intersections spring into existence just because of a changed
projection because a node ends up on the other side of the straight line
used to approximate way sections.

IMHO, all those calculations should ideally be done using great
circles. For most practical purposes using linear approximation with
latlon directly is probably good enough for most practical
purposes. Using Mercator for this might give better results.

Whatever the model is, I think the same one should be used for all
calculations. This might result in intersection points to jump a little
on the screen, but the same operation will always lead to the same
result, which I consider more important.

What do you think?

Matthias