[OSM-dev] Altitude data & (cycle) route profiles

[Andy Allan]

2008/3/27 Sjors Provoost <sjors at sprovoost.nl>:

> My core objectives / deliverables are:
>  import SRTM data as nodes (points) in OSM, for Australia
> estimate the altitude of each node in Australia from the SRTM nodes
> display (on the fly) an altitude profile given a route (a sequence of nodes)
> estimate the altitude of each node in Australia from nearby GPS traces
>  analyze the difference between both methods

> It would be great if I can get some feedback on my proposal before the
> deadline, so I can improve upon it.

Hi Sjors,

Firstly, good luck with your proposal, it sounds quite interesting to me.

If I can make a suggestion it would be to think of the heights along
each way, instead of just at nodes. If you look at the cycle map at
http://www.gravitystorm.co.uk/osm/ you can see SRTM contours with OSM
data overlaid. It's quite possible for a way to be straight yet cross
a valley or a peak, and if you only look at the nodes at each end of a
section you would miss this data. This is especially apparent for long
straight features like motorways or roads in the USA where the gap
between nodes can be many hundreds of metres or even kilometers, and
the same may apply to Australia too. So instead of importing the
heights as points and estimating the height of each node, I would
suggest a different approach:

* Import the SRTM data into a spatial database (i.e. postgis) as
polylines (contours)
* Calculate the points along the OSM way where the way intersects a contour
* Use these points as the height data for the way

Cheers,
Andy