[OSRM-talk] new api table and geometry
daniel at mapbox.com
Fri Apr 15 19:56:20 UTC 2016
Strangely enough, we don't actually have the geometry. We find a path across the Contraction Heirachy
routing graph, this may only have a small handful of edges. We can sum these edges to get the route
duration, but to get the actual geometry or distance, we then have to "unpack" those edges.
The table plugin doesn't do this unpacking step. It gets the durations easily, but would be significantly slower
if we also had to report back the route geometries. The API response would probably also be huge (10s or 100's of MB?) for any
non-trivial number of route pairs in the table. To support that, we would need a way to stream the response
asynchronously to the HTTP client, otherwise a couple of requests could use up all the RAM on the server.
Things are never as simple as they seem :-(
> On Apr 15, 2016, at 12:45 PM, Michal Palenik <michal.palenik at freemap.sk> wrote:
> that is what I already do, but it means a lot of (unnecessary)
> connections. I assume the geometries are already available when
> computing the duration.
> I was hoping for a "documentation lacking behind development"
> On Fri, Apr 15, 2016 at 04:09:49PM +0200, Daniel Hofmann wrote:
>> If you check the v5 spec you linked, you will see only Route, Trip and
>> Match providing a "geometries" option.
>> What you can do is this:
>> - do a Table request from your position against all Bus / Tram stops in the
>> area / in a buffer of a few kilometers
>> - pick n shortest routes from the Table response and temporarily store
>> their destination coordinates
>> - do n Route request from your position against the n destination
>> coordinates and extract the geometry
>> Daniel J H
>> On Fri, Apr 15, 2016 at 3:49 PM, Michal Palenik <michal.palenik at freemap.sk>
>>> within the new api, I am trying to find how to get geometry (together
>>> with perfect duration). is it possible?
>>> or do I have to make N*M queries for all the possible combinations?
>>> I am trying to make a service like "show me the routes to the closest
>>> bus/tram stops" : http://epsilon.sk/mhd/
>>> michal palenik
>>> OSRM-talk mailing list
>>> OSRM-talk at openstreetmap.org
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> michal palenik
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