[Proj] WGS84 to Minnesota State Plane South

[Gerald I. Evenden]

On Thursday 03 January 2008 11:10 am, Arno Gerretsen wrote:
> Thanks Anthony, your proj string helped me solving the problem. It
> turned out to be a problem with the meter to feet conversion. In the
> stirng I used I had tried both +units=ft and +units=m with my own
> multiplication by 0.3048 to get meters. Now it turns out that is where
> the problem was, I had to use 0.3048006 as you did. I did not know there
> was a different between a foot and a US survey foot.

Indeed, there IS a difference as I well know when I was first putting together 
projection software in the '80 and spent many an hour trying to reconcile the 
differenced between an earlier version of proj and gctp.  FINALLY, I 
discovered a mention of the difference between the foots in Snyder's 
manual---one lonely sentence!

> But it seems that the proj library also uses the 0.3048 factor when I
> set the units to feet, is that what it is supposed to do?

Old standard USGS 'proj -lu' and current lproj lists units conversions 
understood internally.  Thus for the various foot conversions you will see 
listed

         	...
           m 1.                   Meter
 	...
          ft 0.3048               International Foot
         	...
       us-ft 0.304800609601219    U.S. Surveyor's Foot
 	...
      ind-ft 0.30479841           Indian Foot
	...
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