[OSM-talk] altitude information

Rainer Dorsch rdorsch at web.de
Thu May 31 16:45:30 BST 2007


Using the NSA data sound much better than GPS data for me. So osm could use 
NSA data and to avoid Frederik's szenario the data could be 
enhanced/overwritten in critical regions (?).

Thanks,
Rainer

Am Donnerstag, 31. Mai 2007 03:07 schrieb 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'
> >
> > _______________________________________________
> > talk mailing list
> > talk at openstreetmap.org
> > http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk

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Rainer Dorsch
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