[mkgmap-dev] Sorted apply of relations, filtering out duplicate ref

Tue Apr 6 13:45:39 BST 2010

The current best practice seems to be to split bus route relations into
two, with different "from" and "to" attributes.  See for instance the
"sketch-route" links for the bus routes HSL 731 and HSL 742 that I defined, at

http://wiki.openstreetmap.org/wiki/Finland:HSL/bus#Linjat

or the direct links

http://78.46.81.38/api/sketch-route?534623&532590
http://78.46.81.38/api/sketch-route?375387&534624

The problem with this approach is that the current mkgmap "apply" would
copy the bus route ref from each relation to the two-way street sections
twice.  Also, if the start and end stops are shared between the relations
as they are for these examples, those bus stops would get the route ref
twice.  The apply_once that I implemented would be of no help.

I think that the relation processing should be changed in a way that gives
the processor a collection of all relations.  I implemented a patch to that
direction that does not change the behaviour yet.  I would like to do something
like this:

SELECT UNIQUE ref FROM relations WHERE type=route AND route=bus ORDER BY ref
APPLY { set route_ref=$ref; }

I hope you get the idea.  I do not actually propose any SQL-like syntax;
the above is for illustration purposes only.

Best regards,

	Marko
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