[OSRM-talk] Polyline Encoding, &geomformat=cmp and Coordinate Hinting

Dennis Luxen luxen at kit.edu
Tue Aug 20 11:11:14 UTC 2013


Hi,

> While trying to use the API of the demo server at
> router.project-osrm.org I stumbled upon some things which puzzle me
> and I hope you can me help out there.
> 
> First, the wiki page on "API usage policy" requires clients to query
> the route geometry by the parameter "&geomformat=cmp", however I
> cannot see a difference in the returned json. That is the value of the
> "route_geometry" attribute does not seem to change at all, whether I add
> "&geomformat=cmp" to the URL or not. Is this is already the default?

Yes, this is default. The wiki has been updated.

> […]
> Second, (and this might be related to the first) it seems that either
> I am missing some subtleties in the Google's Polyline Algorithm Format
> or the coordinates which are returned by demo server are off by a
> factor of ten.

It is not off by 10 but rather more precise than the previous implementation. See the Wiki page for a link to a proper JavaScript implementation of the decoder.

> Third, the "Server API" wiki page specifies that &checksum=$value
> should be added to the URI when using coordinate hinting, where $value
> is drawn from the last query's hint.checksum attribute. I noticed
> however, that in all responses I checked in the last week (about a
> good two dozen, which I checked manually) that this value is always
> 1373382413.
> Again, am I missing something? If not what point does this value serve?

It may change at the servers discretion.

> Turned out longer than I expected, hope this is not too much to ask,
> thanks in advance.


--Dennis






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