[josm-dev] Geometric calculations and projections

[Matthias Julius]

Robert Scott <lists at humanleg.org.uk> writes:

> On Tuesday 08 December 2009, Matthias Julius wrote:
>
>> In other words: if the current projection makes circles look like
>> eggs then I would expect this to be true for both the imagery and
>> the circles created by AlignInCircleAction.
>
> Yes, I understand that, but a user tracing imagery will probably be
> expecting the application to behave like a drawing application, with
> an 'extrude' operation extruding perpendicular to the object as seen
> on screen, not going off in some random direction that it thinks is
> clever. Some users don't understand/want to care about projections,
> and just want to draw things 'as-seen'. Take for example a straight
> edged object that's non-square, but happens to be distorted vaguely
> inversely to the map distortion, so that it appears nearly square on
> screen. A user wishing to trace it would get puzzled and frustrated
> with an extrusion going off in the seemingly wrong direction.

I would expect a square building which gets distorted by the
projection is much more common.  So I think OrthogonalizeAction is
more useful if it produces real world square angles.

JOSM is not a vector graphics application, it is a mapping
application.  IMO it should always (try) to do the correct thing.  If
users get confused by unexpected behavior (unexpected by them) it
needs to be explained to them.

> I don't know if I'm explaining this very well, but my point is I think
> maintaining the option to do operations in screen space is valuable,
> even if it is not the default.

OK, it might be useful to have the option to work in screen
coordinates, but, IMO the default should always be to work in the
real world.

Matthias