[mkgmap-dev] r3165 in via_ways branch

Thu Apr 3 09:58:46 BST 2014

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

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

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