[mkgmap-dev] r3165 in via_ways branch

Thu Apr 3 10:10:57 BST 2014

On 03.04.2014 10:58, Gerd Petermann wrote:
> Hi Felix,
>
> the via_ways branch tries to implement the information that is stored 
> in restriction relations:
> http://wiki.openstreetmap.org/wiki/Relation:restriction
>
> The Garmin format also has a so called "route restriction". It allows 
> to say
> something like "if you come from node n1 travaling on arc a1 to point 
> n2, you are
> not allowed to travel on to point n3 via arc a2.
> The so called 4 node restriction is similar : if you come from n1 on 
> a1 via n2 and n3 on arc a2 you
> are not allowed to continue to n4 on arc a3.
>
> So, it has nothing to do with invisible ways.
>
> What you are asking for is an algo similar to that for the 
> --adjust-turn-headings option.
> I don't think that we really need invisible ways for that, it should 
> be enough to
> manipulate the angle between the roads which is stored in the img file.
> My understanding of the Garmin algo is that it doesn't like sharp angles,
> so I am pretty sure that the angle has an effect on routing.
> I'll do a few experiments with that.
>
> Gerd
Ah okay. Now I got it.

Well for car navigation we don't need invisible ways. I'm pretty sure 
also playing with angles won't really help much except in some special 
cases. The street layout in general is good enough - as there are 
usually via ways for cars to cut down sharp angles in real life anyhow.

For cycling this is not the case. Actually real invisible via/junction 
was wouldn't be needed everywhere. Only on/off/between those lines that 
we define as "cycleworthy". The higher the "road-speed" the more it's 
needed. Also on many junction 2 via ways would be enough
as
           /
____/___
      /
    /

here for example only in the right top corner and left  lower corner the 
angle matters while the angles are fine on the other to combinations.
>
> ------------------------------------------------------------------------
> Date: Thu, 3 Apr 2014 10:42:57 +0200
> From: extremecarver at gmail.com
> To: mkgmap-dev at lists.mkgmap.org.uk
> Subject: Re: [mkgmap-dev] r3165 in via_ways branch
>
> Hi Gerd,
> I haven't really understood what the via ways branch is doing...
>
> Could you explain it again?
> Is it only about restrictions?
>
>
> What could really improve the maps for me would be short invisible 
> short via ways on all intersections in order to reduce the turn angle...
> So instead of
>
>       |
>       |
> -----|------
>       |
>       |
>
> make every intersection (on those places where the angle is over 60°) 
> look like
>       |
>    / | \
> -----|------
>    \ | /
>       |
>
>
> Basically building short invisible via ways (if invisible routing 
> lines are not what this is about, then just give a style/command 
> option possiblity to define the type and then set it invisible in the 
> typfile) for routing (basically the same as highway junctions are in 
> reality, just smaller but serving the purpose of having no sharp turn 
> angle).
> I'm pretty sure this would improve routing a lot for my maps, but this 
> is only an assumption as I cannot build large maps to try it out... 
> (the via ways should'nt be straight as in the above example but of 
> course round to minimize the angle. Length of 10m is long enough - so 
> make em consist of 3-4 points).
>
>
> On 03.04.2014 09:28, Gerd Petermann wrote:
>
>     Hi all,
>
>     I think r3165 is ready for a deeper test.
>     Changes compared to trunk:
>     - handling of RouteRestrictions was mostly rewritten to make sure
>     that mkgmap doesn't
>     write wrong restrictions to the img file (this was possible when
>     different roads connected the same points
>     with direct arcs)
>     - added support for restrictions with one via way (see below)
>     - added support for tag type=restriction:*  , e.g.
>     type=restriction:motorcar
>     - added support for tag restrection:*=<turn> , e.g.
>     restriction:motorcar=only_left_turn
>     - added support for no_entry and no_exit restrictions
>     - improved log messages for invalid or possibly obsolete
>     restriction relations
>
>     Reg. via ways:
>     According to NodCheck in the display tool the data written by
>     mkgmap r3165 is correct,
>     but I found no effect on routing :-(
>     Up to now mkgmap adds a 4 node restriction to both end points of
>     the via way.
>     Maybe there is a bit in a header which has to be (un)set, but I
>     can't find any.
>     Multiple via ways are not yet supported, but partly verified to be
>     correct.
>     Maybe I'll look at that when we see an effect on routing for a
>     single via way.
>
>     @Steve: Do you see any effect of them in your maps?
>     If yes, what might be wrong with the data written by mkgmap?
>
>     Gerd
>
>
>
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>
>
> -- 
> keep on biking and discovering new trails
>
> Felix
> openmtbmap.org &www.velomap.org  <http://www.velomap.org>
>
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-- 
keep on biking and discovering new trails

Felix
openmtbmap.org & www.velomap.org

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