[Openstreetmap] Experiences with SRTM and VMAP data

[Schuyler Erle]

* On 29-Apr-2005 at 12:46AM PDT, Jeremy Stocks said:
> I would like to download SRTM data for my area.
> 
> Can I ask the Openstreetmap community what were your experiences
> here? What is the data quality like?

The SRTN data is 90m resolution; i.e. better than nothing but not
great. Also, it has a lot of holes - null data areas that come up as
-32768m above sea level in the TIFF files - particularly in steeply
inclined areas and over water features, where (one assumes) the
radar signal must have been deflected rather than reflected. You can
clean the null areas up in GRASS using r.fillnulls, but Abhijit
Menon-Sen's experience was that the spline interpolation tended to
make some of the Himalayas a bit flat-topped.

> How good is Vmap level 0 data for its roads coverage? Anyone have
> any experiences there?

The VMap0 data has motorways and a lot of A roads for most of the
world. However, this data has been significantly generalized, so don't
expect terrific accuracy at small scales.

SDE