[GRASSLIST:2964] I made a mess with the coordinates and datum. and now?

Antonio nightnavigator at libero.it
Tue Jan 22 15:51:13 EST 2002


I'm sorry if I'm reposting the same message but I actually forgot to edit the subject header when I last sent it so maybe many didn't read my message thinking it was belonging to another thread.
So I just add the message I already sent below.

I decided to start using Grass for my thesis some weeks ago and only now have
 realized that I've made a huge mistake with the georeferencing procedure.
What I did in the begining was to import a tiff scansion of some topographic
 maps so that I could digitalize the elevation curves and thus build my DTM.
When I built the GRass DB I selected the UTM coordinate system with th WSG84
The maps were not absed on a WSG84 datum but on a ED50 datum. What I did (and
 here's the mistake) is that a gave i.points the coordinates for rectifying in
 the ED50 datum instead of the WGS84 datum. Thus my Grass DB is shifted of some
 80-100 meters in lat and long. This might not seem much but if we consider
that the scale of the maps I imported is 1:25000 , 100m becomes too much for a
correct tollerance.
Not being very expert with grass, I wondered if there was a way out, I mean,
+must I begin digitailizing from the begining in a new GRASS DB with the correctdatum or can I fix things in the current DB (by DB I mean location-mapset in
grass terminology).
Must I use i.points again or what.
I wouldn't like to through away 6 weeks of work :-|

Thanks and cheers.
                 Antonio Gennarini
                Crecchio, CH - ITALY
Earth Science student at University "G. D'Annunzio".
     Join th GNU generation, start from LINUX.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 244 bytes
Desc: not available
Url : http://lists.osgeo.org/pipermail/grass-user/attachments/20020122/832e8210/attachment.bin

More information about the grass-user mailing list