Hi:
You could try lat=a+bx+cy+dxy+ex^2+fy^2+.....
long=j+kx+ly+mxy+nx^2+oy^2+.....
where lat and long are decimal degrees and x and y are the AutoCAD x and y's. and solve for a b c .. and j k l .. by least squares. How many terms and known points you need depends on area of map. You should hold out a few points from least squares and use these to check the formulas. There is danger outside the area of known points and this method is sensitive to errors.
bob sandefur
SungWon Choi <swchoi@esi3.geop.umanitoba.ca> 07/28/98 01:31PM >>>
Hi! everybody..
This problem is not about grass..
but I'm sure somebody can solve this problem...
My problem is the following..
I have a vector file which was digitized in AUTOCAD by Calcomp
digitizer.
when I digitized it, the table coordinates were not real projection
coordinates and the projection system was unknown.
Now, I know the latitude/longitude of some points in this map. so I'd
like to convert the table coordinates of the vector file to the real
projection coordinates(lat/long) with some reference points(for example,
island).
Is there any possibility to do that in Autocad or GRASS..?
Thanks in advance..