[GRASSLIST:3295] SRTM data are not truly projected?

GRASS GRASS user
1

Hi all,

I'd read this on SRTM_Topo.txt from srttm download site

############# Quoating ###################################
This sampling scheme is sometimes called a "geographic projection", but of
course it is not actually a projection in the mapping sense. It does not
possess any of the characteristics usually present in true map projections,
for example it is not conformal, so that if it is displayed as an image
geographic features will be distorted.
###########################################################

Does this mean I need to rectify SRTM data in order to make coincident
with a MrSID image?

Thanks,

Roman

2

On Wed, Apr 28, 2004 at 05:38:15PM +0200, tatel@euskalnet.net wrote:

Hi all,

I'd read this on SRTM_Topo.txt from srttm download site

############# Quoating ###################################
This sampling scheme is sometimes called a "geographic projection", but of
course it is not actually a projection in the mapping sense. It does not
possess any of the characteristics usually present in true map projections,
for example it is not conformal, so that if it is displayed as an image
geographic features will be distorted.
###########################################################

Does this mean I need to rectify SRTM data in order to make coincident
with a MrSID image?

You may fetch the SRTM import script here:

http://mpa.itc.it/rs/srtm/
* 'srtm_generate_hdr.sh': general shell script to make GeoTIFF from
      original SRTM90 files. Requires GDAL tools installed.

* 'r.in.srtm': GRASS script to import original SRTM files.
    Requires above script to be installed in PATH. Fixes the INTEGER
    encoding, applies color table. To use in Lat/Long LOCATIONS (WGS84,
    to be precise EGM96).

Hope this helps,

Markus

PS: It seems that you have to reproject to non-LatLong before
    using r.fillnulls.