[GRASSLIST:3331] Re: Correcting SRTM with MrSID images

Markus Neteler neteler at itc.it
Mon May 3 08:01:38 EDT 2004

Hi Roman,

since you write that you have been using MrSID data
(did you use 'mrsiddecode'?), there is a probability
that either datum and/or ellipsoid are not matching.

>From GRASS 5.3 onwards r.in.gdal is performing a test
to avoid that a user imports wrong data into a location.

You should verify your original data sets and compare
with the current location settings.

See also
how to use gdal_translate to assign new projection info
to a GeoTIFF file (I had to do that because 'mrsiddecode'
doesn't transfer this information when converting MrSID to

Hope this helps


PS: The GSHHS vector shoreline data are not bad.

On Sat, May 01, 2004 at 05:53:07AM +0200, tatel at euskalnet.net wrote:
> Hi all
> I'm using r.mapcalc to get a raster layer to mask sea in SRTM data.
> r.mapcalc red=r#image (good on bare rocky,beach or concrete coasts)
> r.mapcalc green=g#image (good with vegetation)
> r.mapcalc red2='if(red<50,null(),red)'
> r.mapcalc green2='if(green<75,null(),green)'
> r.mapcalc final='if(isnull(red2) && isnull(green2) && srtm<10,null(),srtm)'
> This gives me a shoreline as good as the one I made by hand with
> v.digit.There is still some speckle, but it can be eliminated with
> little work.
> Unfortunatelly I can't register SRTM and image data. After reprojecting
> image from UTM-WGS84 to Lat_Lon-WGS84, it seems to be a shift of about
> 250-300 meters towards W in SRTM from image. More confusingly, this
> shift is more evident in western shorelines than in eastern ones, where
> often it seems even not having shift at all.¿?
> Am I on LSD? Why can't I register the two datasets? How could I do? May
> be this is a dumb question, but is driving me nuts. Any advice, pointer
> or recommended reading would be greatly appreciated!
> Please HELP!
> Thanks a lot,
> Roman

Markus Neteler     <neteler itc it>       http://mpa.itc.it
ITC-irst -  Centro per la Ricerca Scientifica e Tecnologica
MPBA - Predictive Models for Biol. & Environ. Data Analysis
Via Sommarive, 18        -       38050 Povo (Trento), Italy

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