Hi Felix,
I think I found some more rules, but I still need more tests
before I can code a new fix.
I found at least two errors in the v2 + v3 patch, not sure
if they cause harm or if they just prevent good results.
One was in the highest speed calculation, the other in the calculation
of the needed heading change (some angles were not enlarged, others
were enlarged too much)
Here is what I learned so far:
1) The time penalty for a turn depends on the angle and the sum of the
road speed values of the arcs which are used.
(I thought that I have to look at the maximum (or minimum))
2) the sum of speeds gives a factor which is mulitplied with a value that depends
on the angle. The threshold values for the sum of speeds:
0,1 : 0
2,3 : 1
4,5 : 2
...
12..13: 6
14: 7
2) penalties (for a car) are
steps of 60s for angles below 22.5° (0s, 60 s, 120 s, 180s, ...,420s)
steps of 12s for angles > 22.5 and below 45 (0s ,12s , ..., 84s)
steps of 6s for angles > 45 and below 67.5 (0s, 6s, ...42s)
steps of 3s for angles > 67.5 and below 90 (0s, 3s, ..., 21s)
3) The penalty is always completely added to the travel time of the 2nd arc.
TODO:
- The above values are for a right turn in a drive-on-right area. I still have to
check left turns.
- I also have to measure the effect on bicycle routing and maybe other vehicles
- The effect of multiple arcs. They have an effect on the precision of the stored
heading values. Not sure how this changes the results.
I guess that Garmin will only use an arc with a high speed when
that is long enough so that the higher speed weights out the penalty .
A few tests show that it typically prefers the slower roads at the junction
with the sharp angle, and "jumps" on the faster road at the next node.
If you think that I should also look at other parameters, please let me know.
Gerd
Date: Sat, 5 Sep 2015 15:17:17 +0200
From: extremecarver@gmail.com
To: mkgmap-dev@lists.mkgmap.org.uk
Subject: Re: [mkgmap-dev] [Patch v3] sharp angles
Yes - I think for the start and end of a route - the algo will choose topmost route only. For inbetween sections however not - there it chooses the best - at least according to my tests a few years ago...
There is a max of 6 or 7 roads lying on top of each other - if more it will produce a routing error and not go there at all.
And yeah - I also don't know what's best. V2 seemed best to me so far.
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