[OSM-talk] 1) Messy Overlapping 2) Messy Layers 3) Bridges 4) Trunk/primary 5) Forum

[Jochen Topf]

On Sun, Feb 11, 2007 at 12:09:42PM +0000, 80n wrote:
> On 2/11/07, Tom Chance <tom at acrewoods.net> wrote:
> >
> >Ahoy,
> >
> >On Sunday 11 February 2007 00:53:25 Ben Robbins wrote:
> >> 5 problems I have...please split up into seperate topics for
> >reply.  Check
> >> image for refernces..
> >>
> >> http://i57.photobucket.com/albums/g226/ben_robbins_/osm3things.png
> >>
> >> 1)  Where different highway types meet at junctions it usually renders
> >> quite a messy overlap of the core where 1 of the cores renders later and
> >> has a rounded end.  In just adding an additional tag (for the purpose of
> >> the example I have added core=yes) you can make selected cores render
> >again
> >> later and clean up junctions.  What would a good tag for this be?
> >or...are
> >> there better methods of sorting out this asthetical fault?.
> >
> >If things look wrong in the slippy map or your own Osmarender renders,
> >don't
> >tag your way around the problems! Report the problems with mapnik and
> >osmarender and wait for them to be fixed, but keep the tags in the
> >database
> >clean.
> 
> 
> Actually this kind of experimentation and innovation should be encouraged.
> If people play with rules files and demonstrate potential solutions, that's
> a much more constructive approach than submitting a fault to trac and then
> wondering when it will get fixed.
> 
> I think the core=yes modification is quite interesting.  The end result
> looks good and is an improvement - but maybe there is a better way to
> implement it.  Now that Ben has demonstrated how good it looks, I think we
> are at least one step closer to a solution.

Generally there is no need for the core=yes element. As far as I can see
the problem only occurs in T-shaped junctions (or topological similar)
where the through road has a "lower classification" than the ending road.
So if there is a primary road ending at a T-junction and the
unclassified road goes through the same junction, you'll see the ugly
round knob in the junction. But it certainly is computationally possible
to find those T-junction cases and re-order the drawing of the ways.

Problem is: This gets messy once we are not only looking at one junction
but at a whole road network, and it gets really messy once we take layers
into account. But I don't see how the core=yes helps here. It only makes
things more complicated. Certainly for the person doing the tagging.

And another reason why the core-thing is an ugly hack that doesn't even
work: It only works as long as the highway casing is always the same
size. See the enclosed png for an illustration of the problem.

The core of the problems seems to be that we assume that road junctions
are point objects and have no size. But thats not the case once you draw
roads which have a width.

btw: The google map rendering has the same problem. Sometimes it is even
worse, because sometimes they not only have the ugly round core thing,
but the casing is drawn on top also. See for instance just south of the
Golden Gate bridge the short stretch of highway 1. (Problem appears only
in some zoom levels.)

Jochen
-- 
Jochen Topf  jochen at remote.org  http://www.remote.org/jochen/  +49-721-388298
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