[josm-dev] self-intersecting ways

[Klaus Dietrich]

am 26.03.2010 12:36, schrieb stefan at binaervarianz.de:
> I heavily oppose that! Purposefully map something in a wrong place is just
> wrong in my opinion.
Well, it's not purposefully wrong, but reasonably generalized. Besides,
how would you map the landuse in the correct place? Map the axis of the
road, then map the border of the left landuse, then the border of the
right landuse? Or the axis and width of the road, then project the
coordinates of the landuse? You end up with three nodes orthogonal to
the axis.
> Points and shapes are defined by coordinates, not by there relation to
> other nodes or ways.
Sure, in the database, but is the landuse really defined with its own
coordinates?
> You can't rely on the renderer to expand the road and correct your
> misplaced landuse.
You have to, thats generalization and it's necessary for any map with a
scale lesser than say 1:5000.
> What's the logic for mapping then? I map to the border of the landuse if it
> stands on its on, but to the next road if there is any?
Yes.
> What if the road gets deleted or moved? Should the landuse be moved also?
You mean if the physical road changes? Of course. It has to be re-mapped
then.
If the road still exists and the way is deleted it's an error and the
way should be restored. If the way must be moved because it was not
precise you simply move it and it stays correct. Whereas with your
approach you would have to move 3 different nodes at once which becomes
a problem in bends, because the radius changes.
I've often seen roughly mapped forest (landsat, ~20m maximum precision
with calibration) next to a road. Now someone moves the road in
direction of the forest because it was imprecise, but does not move the
forest. You now have forest to both sides of the road, which is really
wrong.
Had both been glued together it would still be correct.
> Wherever I've seen landuse mapped near a road, it was mapped to its
> physical extends, leaving free space to the single way defining the center
> line of the road.
> If anyone decides to map the road as an area later, he don't have to touch
> the landuse.
That's a point though, but we're very far from that.
> Or take the practical approach: If you are standing on asphalt, but your
> maps says you're standing on grass, who is wrong?
They are both right, but you are using the wrong map for the task. You
either need a map with generalization or you shouldn't demand such a
high precision. Remember, we are using comsumer-grade GPS. Precision
higher than say 3m will require high effort with these devices.
> Undefinied (e.g. empty space) is far better that blatant wrong.
Right.
> Sorry to hijack this thread, but I just had to comment this.
Same for me.