Transformation question...

Katie Alvin kalvin at
Tue Dec 8 10:39:50 EST 1998

> Vangelis Filippidis wrote:
> Dear GRASS community,
>    I recently found some vector data of an area that i'm interesting,
> in a X-Y unreferenced system, and i want to "put" them in my mapset
> (UTM - Zone 34 - International), that i'm working.
>    How i can transform them, so i can use them with my rest vector
> data?
>  I would very appreciate any ideas about this.
> Thank you in advance,
> Vangelis.


If you can locate at least 4 points on your "unreferenced" vector file
that you can get known UTM coordinates for,
you can use v.transform, however this will only work on an ascii file.
Bring your new file into your mapset as a binary vector coverage, then
convert the file to an ascii coverage using v.out.ascii. Determine at
least four reference points and make a file
called "points" or something in the format: 

X1 Y1	UTM-Easting1 UTM-Northing1
X2 Y2	UTM-Easting2 UTM-Northing2
X3 Y3	UTM-Easting3 UTM-Northing3
X4 Y4	UTM-Easting4 UTM-Northing4

where each row is a different reference coordinate pair delimited by
spaces (no header or anything). Run the v.transform script to
generate a new ascii coverage. (It's easy to run interactively.) Then,
finally, use to convert the newly referenced ascii file back
to a binary vector file. I did this a while back to convert a geodimeter
file to UTM and it is quite simple! I only used 4 points and got an RMS
of 2.9.

Katie Alvin
FOCS/FGI/GIS Specialist
USDA NRCS, Bozeman, MT
kalvin at

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