[GRASSLIST:4157] Re: state plane - newbie

[Richard Greenwood]

Eric,

Thanks to your help I'm quite a bit closer that I was. Here is what I've 
done, please tell me if you seen anything obviously stupid. I'm working in 
Wyoming NAD83 state plane using US Survey feet.
1. Created a link such that "state27" points to state 83
2. Added definition for my Wyoming zone (because it wasn't in there) and 
defined the false northing & easting in meters.
3. Created a location, bounded in feet.
4. Changed the PROJ_UNITS meters definition from .3048 to .304806096 (US 
Survey feet)

My g.region -l now shows the correct lat/lon for the location I created and 
things look correct when I import them. However areas and distances are 
completely wrong. ( A real world distance of 660 feet is displayed as ~1450 
meters and a 10 acre polygon was reported as ~105 acres) So I guess I'm 
still doing something wrong. Partly I'm not sure how and when the 
PROJ_UNITS gets called into play.

Thanks for reading this, any suggestions or pointers would be welcomed.
Rich


-At 06:28 PM 7/23/2002 -0700, you wrote:
>On Mon, Jul 22, 2002 at 09:43:13PM -0600, Richard Greenwood wrote:
> > I am creating a new location in state plane, wyoming west zone, nad83, 
> feet.
> > But g.region.sh -l (print region settings in lat/lon) returns latitudes 
> that
> > are off by about 1 degree, and longitudes that are off by 8 degrees. I 
> am new
> > to GRASS so maybe I am doing something wrong. Where would I look for the
> > definitions of FIPS code and coordinate system parameters?
>
>You probably noticed, GRASS didn't ask you whether you wanted state
>plane 83 or state plane 27.  Well, it's kind of hardwired to use
>state plane 27.  To get around that:
>
>$ cd grass5/etc/
>$ mv state27 state27.real
>$ ln -s state83 state27
>
>Do that before creating locations and importing data.
>
>Also note, that GRASS uses the international foot for it's feet to
>meters conversion.  You'll have to find out whether Wyoming uses
>the statute foot vs. the international foot, if this discrepancy
>would be important to you (it was intended that all states use
>meters for state plane 83, so now it's just a mish mash...) You
>can change the unit conversion in the PROJ_UNITS file if needed.
>
>--
>Eric G. Miller <egm2 at jps.net>


Richard W. Greenwood, PLS
Greenwood Mapping, Inc.
Rich at GreenwoodMap.com
(307) 733-0203
http://www.GreenwoodMap.com