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[mkgmap-dev] Possible maxspeed patch

From MarkS OSM at redcake.co.uk on Wed Aug 26 20:49:02 BST 2009

Florian Lohoff wrote:

> Wouldnt it make sense to make it possible to apply factors based on road
> class to the maxspeed setting?
> e.g unclassified -> maxspeed*0.6 
>     tertiary -> maxspeed*0.8
> OTOH this should all be the responsibility of the routing engine
> and at the moment as i understand we abuse the maxspeed (OSM) to set
> an "average speed" in the Garmin dataset - not something like a 
> speed limit which is obviously broken anyway and just some
> idea to make use of the maxspeed ...
I'd come across this whilst setting up the patch. The main road near me 
has maxspeed=50mph on it. This then gets converted to kilometers and 
just scrapes over the 80kph barrier and gets a road class of 5 which 
effectively assumes you will never drop below the speed limit.

My feeling was that there might be a case for another patch which 
reduces the maxspeed by a certain amount (eg. 5mph or by 20%) when 
deciding which road class to allocate. This probably needs (yet) another 

My patch isn't really concerned with how the maxspeed tag is converted 
to a road class. It is aimed at deciding whether to use set the road 
class from the style file, the maxspeed tag (however that is translated 
to road class) or both.

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