converting coordinates.. NOT ABOUT GRASS exactly

[Robert L. Sandefur]

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 at 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..

--
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SungWon Choi                | email: swchoi at esi3.geop.umanitoba.ca 
Dept. Geological Science    |
University Of Manitoba      |
Phone : 204-474-7343        |
FAX   : 204-474-7508        | Good Luck!
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