[GRASSLIST:3320] Correcting SRTM with MrSID images

tatel at euskalnet.net tatel at euskalnet.net
Fri Apr 30 23:53:07 EDT 2004

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,


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