[OSM-talk] Right angles and aspect ratio

Andrew Errington a.errington at lancaster.ac.uk
Tue Jul 5 02:09:10 BST 2011


I have recently noticed that JOSM does not produce pleasing right angles
when I select "Orthogonalise Shape (Q)".  (I will refer to this as
"squaring" because "orthogonalising" is too long).

I added some new building outlines in JOSM and squared them, but they look
terrible when rendered.  So, I went to Potlatch 2 and used the 'Make
right-angled function' to square them and now they look fine.

Furthermore, I went to some of the older buildings/areas that I remember
squaring in JOSM (I generally use JOSM).  If I square them again, they
change.  This shouldn't happen.

Here is an example:


Building 105 and 106 (centre) were edited and squared in JOSM, then
squared again in Potlatch.  They look good.

Geochang-eup office (to the right) was entered and squared in JOSM a long
time ago.  It looks fine.

King's Club supermarket (below) was entered and squared in JOSM today and
looks bad.

The cluster of apartments in the upper-left were entered and squared in
JOSM today and look bad.

If I were to load Potlatch and square the bad ones they would move, and
they would look good.

How they look is not really the point.  The point is that JOSM now behaves
differently to before, and differently to Potlatch 2.  I have also noticed
that JOSM's "Align Nodes in a Circle (O)" function makes circles look
squashed.  In addition, the aspect ratio display looks wrong.  It looks
like it's spread out from side-to-side.

Here's another good example.  It's a circular roundabout in the town. 
View it in JOSM:


If you turn on background imagery (yes, it's offset a little) you will see
that the photo looks 'squashed' but that the way representing the
roundabout looks squashed too and matches the photo.  I originally drew it
in JOSM and used 'O' to make it round and it matched the photo then too.

Now if I press 'O' it *looks round on the screen* but will be rendered in
a squashed way in Mapnik.  I am sure that if I made it 'round' in JOSM
then saved it and made it round in Potlatch it would change shape again.

Has anyone else noticed this?  I think it's an issue with JOSM, but I
can't say when it appeared.  I will raise a TRAC ticket unless of course
it's something to do with my computer.  I am running the latest JOSM 4064.

Thank you,


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