[OSM-talk] altitude information

[Nick Black]

Raw SRTM data has a worldwide vertical accuracy better than 10m, the RMSE is
something like 5m or better - so its way more accurate than GPS.  The
horizontal accuracy of SRTM is also pretty good - around 10-15m.  The issue
that that the NSA only release 90m resolution data for most of the world, so
if there was a 30m wide canyon, it *might* not show up on the SRTM.

On 5/31/07, Frederik Ramm <frederik at remote.org> wrote:
>
> Hi,
>
> > Altitude data is already freely available, and GPS precision is really
> > really poor on Z-axis.
>
> I am not an expert here, especially I don't know how good existing
> altitude data is (in terms of lat/lon precision).
>
> I imagine a road going along a ridge; 50m to one side of it you're
> already 500m deeper. Knowing whether the road is on the ridge or in the
> valley is a valuable piece of information (especially, I should imagine,
> for walkers and cyclists).
>
> In this situation, we'd need something like 20-metre lat/lon precision
> on the existing altitude data to determine whether the road is on the
> ridge or in the valley; but we would only need 100-metre altitude
> precision on the GPS track to reliably say where the road is. (I guess
> this is what Rainer meant by high altitude deltas.)
>
> And what about GPSes with built-in pressure altimeters? If we accept
> height data from those, that would revive the old question of how to
> record precision metadata ("this elevation was recorded using an old
> e-trex, don't trust it / this elevation was recorded with a modern super
> duper hillwalking GPS with altimeter and ice crusher...").
>
> Anyway, whatever the answers to these questions are, there should really
> be a little chapter in the Wiki FAQ "why don't you record height
> information" because it is a question that pops up quite often!
>
> Bye
> Frederik
>
> --
> Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00.09' E008°23.33'
>
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-- 
Nick Black
--------------------------------
http://www.blacksworld.net
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