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[mkgmap-dev] [PATCH v1] Fix Nuvi routing regression (rebloat Table A)

From Mark Burton markb at ordern.com on Wed Nov 25 22:29:38 GMT 2009

Way back in September, revision 1228 changed one of the routing data
structures (Table A) to have one entry per road rather than one entry
per arc (a road contains 1 or more arcs). This reduced the number of
Table A entries required which made the maps smaller and, hopefully,
improved the routing because the routing centres could be larger.

However, I have been trying for some time now to find why the routing
is partially broken on my Nuvi 255 for certain combinations of mkgmap
version, extra patches and the options used when compiling the map. The
same maps work fine (as far as I have tested them) on mapsource and
the etrex. Not one routing failure occurred on those that could not be
attributed to something else.

So, after much dicking around with options, patches, etc., I think the
Table A size reduction is the culprit. The attached patch essentially
undoes the good work from September (although this code is simpler than
what was there before). With this, the Nuvi barfs no more. The downside
is that the map has grown again. Can't say whether the routing quality
has changed.

Rolled into this patch is another reversion. The value of
MAX_ARC_LENGTH has been reverted to 75000. Never did believe that was
the real solution.

Please give it a go and report any findings.


PS - Marko, please try this and see if the routing problems you were
experiencing still occur. Also, please try it on your Nuvi user and see
if their problems go away.

PPS - the one pleasing aspect of all this is that if it proves to be a
sensible change, the node-reduction patch that I keep banging on about
will see the light of day.
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