[josm-dev] Geometric calculations and projections

[Matthias Julius]

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

> On Tuesday 08 December 2009, Matthias Julius wrote:
>> What do you think?
>
> It's funny you should say this - I am currently working on a few
> things such as some proper geometry operations.
>
> It started with me doing some work on the extrude function and
> realizing it should really be able to work in real-space rather than
> projected-space. The way I was planning on doing this was to do the
> operation in in 3-space, in cartesian coordinates, then converting
> back to latlon.

I guess local cartesian coordinates would be the best for things like
orthogonalize since that's the way buildings are built.  But, in
practice, using Mercator should be close enough for real world
building sizes.

>
> However, the ability to also do the operation in projected-space is
> quite important I think, as users are often tracing from imagery, in
> which case they will probably want WYSIWYG behaviour on the
> projection. In this vein, the way I was planning on doing it was to
> have a modifier key (hmm most of them are already taken aren't they?)
> to select between 2-space(projection) calculations and 3-space(real)
> calculations.

Well, the imagery is hopefully transformed according to the current
projection.  A roundabout in real world might not look round on the
imagery.  I think it would be just perfect if JOSM would distort the
roundabout in the same way as the imagery.

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.

Matthias