[OSRM-talk] Road speeds and profile restrictions

Richard Marsden winwaed at gmail.com
Mon Sep 21 15:14:51 UTC 2015


Thanks - yes, I'd found the definition of osrm::json::Object and
osrm::json::Value, and went through quite a few variations. I'll have
a look at the boost variant definition.

I didn't know my C++ was so rusty until I tried working with OSRM! I
used to use it a lot, but it was before boost came along.

richard

On Mon, Sep 21, 2015 at 7:15 AM, Daniel Hofmann <hofmann at mapbox.com> wrote:
> First of all, don't use C-style casts, a la `(int)myObject;` as this will
> (in the worst case) degrade to a `reinterpret_cast` and you really don't
> want this behavior.
>
> Now take a look here:
>>
>> https://github.com/Project-OSRM/osrm-backend/blob/e1ac1c4fdc062a0e5c017d268d0a7fcb25bbbab1/include/osrm/json_container.hpp#L84-L87
>
> This is the definition of `osrm::json::Object`. Above it you find the
> definition of `osrm::json::Value`, which is a heterogeneous sum type, making
> use of the following implementation:
>> https://github.com/mapbox/variant
>
> And here is the basic hello world example for the variant implementation:
>>
>> https://github.com/mapbox/variant/blob/bf485dfb59aef26f3ef2183d7c8c1111ad97062b/test/variant_hello_world.cpp
>
> Because it mimics Boost.Variant, please have a look at the detailed tutorial
> here:
>> http://www.boost.org/doc/libs/1_59_0/doc/html/variant/tutorial.html
>
> It shows you among other things how to use the double dispatch visitor
> pattern for extracting values from a variant.
>
> Hope that helps,
> Daniel
>
> On Sun, Sep 20, 2015 at 8:20 PM, Richard Marsden <winwaed at gmail.com> wrote:
>>
>> Steve how did you extract information from the osrm::json::Object
>> returned object?
>> I could covert the Object to string, and then parse it with a 3rd
>> party JSON library, but that seems long-winded.
>> I've already asked this question on the OSM Q&A site but no anwers yet:
>>
>>
>> https://help.openstreetmap.org/questions/45342/extracting-data-values-from-osrms-osrmjsonobject-using-c
>>
>> Text of question:
>>
>> I can receive the JSON result successfully and printing it to the
>> console (as per the online samples), but I am have problems extracting
>> actual field data. How can I extract individual fields as numbers,
>> string, etc?
>>
>> I've tried various forms of casting, but this is what I have at the
>> moment (trying to extract the status value):
>>
>> const int gr_result_code = routing_machine.RunQuery(route_parameters,
>> json_result);
>> std::string sStat("status");
>> auto it = json_result.values.find(sStat);
>> osrm::json::Number vv =  (osrm::json::Number) ((*it).second); // doesn't
>> compile
>> int v = (int) (vv.value); // probably some dodgy rounding here
>>
>> The Number casting is producing compiler errors. I guess I could
>> convert the object to a string, and then using a third party JSON
>> parser to extract individual fields, but this seems very wasteful.
>>
>>
>> --------------------
>> Richard
>>
>> On Thu, Sep 17, 2015 at 8:20 PM, Stephen Woodbridge
>> <woodbri at swoodbridge.com> wrote:
>> > Richard,
>> >
>> > I have already imbedded OSRM into a C++ application and in fact wrapped
>> > that
>> > application into a postgresql database extension. I my case I only need
>> > data
>> > for a city but I was making literally billions of calls to osrm.
>> >
>> > As Patrick said, OSRM makes random access calls to memory and there are
>> > a
>> > lot of variables that come into play like how well the data is clustered
>> > in
>> > memory pages, how many page faults you hit, etc. For your specific use
>> > case
>> > no one will have a good answer for you and you really need to do some
>> > performance testing using the product the way you intend it to be used
>> > and
>> > see what the performance issues are. Maybe you use case is fine. The
>> > OSRM
>> > public service uses lots of memory because it has to support multiple
>> > random
>> > requests anywhere in the world and it can not afford to get stuck page
>> > in
>> > swap. Using swap and an SSD might be fine in your application, and may
>> > be it
>> > won't, but we do not have enough information to consider the problem
>> > more
>> > than to give the standard answer - more memory is faster more swapping
>> > is
>> > slower.
>> >
>> > -Steve
>> >
>> >
>> >
>> >
>> > On 9/17/2015 8:45 PM, Richard Marsden wrote:
>> >>
>> >> Thanks for the quick reply Patrick.
>> >>
>> >>> Presumably I could do the same for world preparation & routing? Have,
>> >>> perhaps a 100GB+ swap file, ideally on an SSD.
>> >>
>> >>
>> >>> This will fall apart when you have some actual load pressure on the
>> >>> system. We need random access to memory, which will create a lot of
>> >>> page faults (== slow). Even an SSD is not even close to memory speed.
>> >>
>> >>
>> >>> You have two options:
>> >>> split the datasets
>> >>> get a bigger server
>> >>
>> >>
>> >>
>> >> I would imagine that is the case for the standard http server. I was
>> >> thinking of using it as a linked library from a C++ program. Splitting
>> >> the datasets by continent is a possibility though.
>> >>
>> >> (writing a C# interface was another thought, but that would be a
>> >> different use case and definitely with smaller datasets)
>> >>
>> >> Cheers,
>> >>
>> >> Richard
>> >>
>> >>
>> >>
>> >>
>> >> On Thu, Sep 17, 2015 at 4:37 PM, Patrick Niklaus
>> >> <patrick.niklaus at student.kit.edu> wrote:
>> >>>
>> >>> W.r.t. the pre-preprocessing you are correct.
>> >>>
>> >>>> What is that extra power used for?
>> >>>
>> >>>
>> >>> Including all sorts of external data sources. Also the logic in the
>> >>> lua profiles is not just replaceable by simple key-value pairs, OSM
>> >>> requires you to handle a lot of special cases.
>> >>>
>> >>>> Presumably I could do the same for world preparation & routing? Have,
>> >>>> perhaps a 100GB+ swap file, ideally on an SSD.
>> >>>
>> >>>
>> >>> This will fall apart when you have some actual load pressure on the
>> >>> system. We need random access to memory, which will create a lot of
>> >>> page faults (== slow). Even an SSD is not even close to memory speed.
>> >>>
>> >>> You have two options:
>> >>> - split the datasets
>> >>> - get a bigger server
>> >>>
>> >>> Cheers,
>> >>> Patrick
>> >>>
>> >>>
>> >>> On Thu, Sep 17, 2015 at 10:06 PM, Richard Marsden <winwaed at gmail.com>
>> >>> wrote:
>> >>>>
>> >>>> I've been evaluating OSRM, using it primarily as a library from C++.
>> >>>>
>> >>>> I believe I've determined the answer to most of the questions, but
>> >>>> I'm
>> >>>> also looking for confirmation.
>> >>>> (I understand the reason for these constraints - the trade-off of
>> >>>> speed vs flexibility)
>> >>>>
>> >>>> First, road speeds are set with 'profile.lua' at the osrm-extract
>> >>>> stage. This filters out unnecessary roads (eg. foot paths for car
>> >>>> routing), but also applies the road speeds.
>> >>>> If I wish to change the speed profile, I need to regenerate the road
>> >>>> network with osrm-extract and osrm-routed.
>> >>>> Correct?
>> >>>>
>> >>>> If I wanted different speeds for the final distance/time
>> >>>> calculations,
>> >>>> I could use the returned route, and apply my own speed table
>> >>>> according
>> >>>> to the road type of each road segment. This would not, of course,
>> >>>> change the route geometry is calculated.
>> >>>>
>> >>>> If I want a shortest route (distance optimized) instead of a quickest
>> >>>> route (time optimized), I need to set all the road speeds to the same
>> >>>> speed and regenerate the network. I.e. osrm does not directly support
>> >>>> the concept of a "shortest route".
>> >>>>
>> >>>> The profile is provided with a LUA file. I had to look this one up
>> >>>> :-)
>> >>>> Looks a useful scripting language, but why is this profile a script
>> >>>> file, and not a simple configuration file of constants (eg. key-value
>> >>>> pairs)?
>> >>>> Seems like an unnecessary complexity - I'd like to understand the
>> >>>> perceived advantages. What is that extra power used for?
>> >>>>
>> >>>> Finally, the memory usage... I saw a reference to the server
>> >>>> requiring
>> >>>> 40GB of memory for pan-European routing. Presumably that could be
>> >>>> offset with a large swap file(?)
>> >>>> A large swap file has worked well when I was testing the US-South
>> >>>> region on an 8GB machine.
>> >>>> Presumably I could do the same for world preparation & routing? Have,
>> >>>> perhaps a 100GB+ swap file, ideally on an SSD.
>> >>>>
>> >>>>
>> >>>> Cheers,
>> >>>>
>> >>>> Richard Marsden
>> >>>>
>> >>>> _______________________________________________
>> >>>> OSRM-talk mailing list
>> >>>> OSRM-talk at openstreetmap.org
>> >>>> https://lists.openstreetmap.org/listinfo/osrm-talk
>> >>>
>> >>>
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