[OSM-dev] SoC Project: Preprocessor to add altitude information to OSM data

Hermann Kraus herm at scribus.info
Wed Apr 8 20:24:32 BST 2009


Hello!

I have applied for SoC to write an preprocessor that adds altitude data to  
ways to allow better bicycle routing, etc.
The complete application text is available at [1] for those of you who  
don't have access to Google's mentor interface.

First some information about me:
I study physics at the University of Regensburg [2] and I'm in the 6th  
term. I already took part three times in SoC and completed all projects.  
My hobbies are computers, electronics, cycling and swimming. I could not  
discuss this proposal earlier, because I was very busy moving to a new  
house. Now that it's over I'll have more time.

I got some questions about my application by Graham Jones  
<grahamjones139 at googlemail.com> and I'll discuss then here:
(Quotes are copied from his mail with permission, my replies are what I  
wrote him with some small corrections/additions)

> The first is what to do with the data - do you envisage it going back  
> into
> the OSM database, or straight to the routing programme?  There is a  
> debate
> to be had about where to put this data - some may not wish to 'clutter'  
> the
> OSM database with it.

The data is not meant to go into the osm database, as it would result in
incorrect data soon, as the users are free to move ways around. What I can
imagine is that somebody processes the planetdump each week and publishes
this dump. Something similar is done with routable garmin maps. This
enables everybody to use the data without having to download all SRTM
tiles and without the computing power.

> The other is slightly more fundamental - I agree that you can fairly  
> easily
> calculate total climb over a way, but my question is whether that is  
> really
> what you want?  I think that most ways do not end at road junctions
> (certainly not the ones I have mapped anyway), but the routing programme
> will be interested in the total climb between road junctions, rather than
> for the total way?

You are obviously right. What do you think about this idea: Instead of
attaching tags to a way I could find all nodes which are shared by more
than one way and then for each part of a way between two intersection
create a relation like this:
type=metainfo
alt_difference=10.6
alt_total=27.3
distance=1032
with the way and the two intersection nodes as members.
The distance is easily computed while doing the other processing. So the  
routing application could skip this step.

> If I am right then rather then your proposal will need closer
> integration with the routing programme - I think the router will  
> pre-process
> the OSM file to calculate distance between junctions - we will want it to
> include altitudes at the same time.

I explicitly tried to avoid a strong integration with the routers, because
we have more than one and I expect even more in the future. Creating a
library might be an option, if you think my idea is not really good the
other way.

However I still would prefer the preprocessor option since this allows to  
publish planet dumps which have the altitude information. When the  
processing is done by the router one has to publish data for each router  
seperatly or the user has to download the SRTM data. I want to make this  
application as userfriendly as possible and what could be more  
userfriendly than having a world file (or excerpt of it) which already  
includes the altitude data.

> I think your proposal to add a relation is an interesting one - it is
> essentially doing the same thing as the routing program will need to do  
> for
> distances - you can imagine doing the same to calculate distance between
> junctions too, which is what the routing programs will do.   I am still a
> little unsure how much benefit is gained by your proposed way of doing  
> it,
> rather than directly incorporating it into a routing program - the  
> routing
> program(s) will need to be modified to read your new relations anyway  
> won't
> they?
> I would be inclined to suggest the two possibilities on your mailing list
> post to see what the others think.

Of course the router will need some support for reading the data. But it  
won't need support for processing SRTM data directly.

I'm also interested in some feedback on this point. What do the people on  
this mailinglist think about it?

Regards,

Hermann


[1] http://r2d2.stefanm.com/soc2009/application2009_altitude.txt
[2] http://www.uni-r.de/




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