[GraphHopper] Understanding GraphHopper Instructions

[Matthias Marquardt]

Hi Peter,

thanks for your time to reply - since I am not 100% confident, if I have
fully understood the core data (yet) I can't answer with a clear 'yes' to
your question, if I want to have turn instructions after every edge (simply
cause I don't know the true meaning of 'edge').

If an 'edge' in the object world of graphhoper (gh) is what I would call 'a
junction or a join' of roads (paths, tracks, trails etc) in the real world,
then indeed that's what I am looking for (some sort of)...

I want to have a instruction every time when I need to "change" the current
trail I am riding on...

When I started the Thread, I did not understood much - concerning how gh is
working. Since with the two given example links I hope it's quite obvious
that there are situations when Instructions are simply missing. While I was
playing around with different kind of vehicles and urban and outdoor
sections, I came to the conclusion, that the InstructionList generation
works solid for urban areas - but not for random hiking paths (or country
lanes).

Finally I realized what was (is?) IMHO the root cause of the missing (or
let me say "my missed") instructions - gh is checking for name or attribute
changes of the edges of the complete graph... Which explains that it works
very good for urban areas (where every street/path comes with an name) -
but also seams to be the root of my issue of missing instructions for
hiking path (and MTB trails) that most of the time are unnamed in OSM.

So my thought/suggestion is, to give every edge that will be parsed from
the OSM data a name - (might be there is already something like a uniqueID
that can be used for this purpose?!) - since then The InstructionList
generating code can 'detect' changes between 'unnamed' OSMWays (with
identical attributes)...

Of course this change have an massive effect on the file size of the
'names' storage - e.g. for complete 'hessen' it grew from 3MB to 16MB...

After I have sorted now my thoughts again - When you asked, if I want to
have a turn instruction for every edge - the answer would be 'no' - not for
every - when it's straight ahead (CONTINUE_ON_STREET) I don't want a
Instruction...

So again - e.g. if there is a different edge attribute (then name) that
could be used/check, I would be more then fine to use that... The only
reason why I used that name-attribute was, that I did not found much else
in the gh sources (except Instruction List) that is using it... So my
thought was, to have as less (unknown) side effects as possible :-)
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