[Proj] WGS84 to Minnesota State Plane South

[Noel Zinn]

FYI, 

The EXACT conversion factor is the ration of two integers, viz.

1200/3937

Noel


-----Original Message-----
From: proj-bounces at lists.maptools.org
[mailto:proj-bounces at lists.maptools.org] On Behalf Of Arno Gerretsen
Sent: Thursday, January 03, 2008 10:11 AM
To: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] WGS84 to Minnesota State Plane South

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.

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?

Arno


On Thu, 2008-01-03 at 23:38 +1100, Anthony Dunk wrote:
> Using my own coordinate conversion program (which calls the PROJ dll),
> I got the following results when converting your test point from WGS84
> lat/lon to US State Plane (NAD83, US survey feet) Minesota 2203, South
> Zone: Easting=2821052.4, Northing=1017159.1. These results are quite
> close to the reference point you gave.
> 
> I couldn't see any differences in the parameters I was passing to PROJ
> compared to yours.
> 
> The PROJ string I'm using for this US state plane coordinate system is:
> 
> +proj=lcc +lat_1=48.7833333333 +lat_2=45.2166666667 +lat_0=43
> +lon_0=-94 +x_0=800000 +y_0=100000 +a=6378137 +rf=298.257222101
> +to_meter=0.3048006
> 
> Anthony.
> 
> --- Arno Gerretsen <arno at agerrius.nl> wrote:
> 
> > Hi,
> > 
> > I am trying to convert some data for a friend from WGS84 lat/lon to 
> > Minnesota State Plane South. I use the proj4 library for that, but
> > the 
> > results do not match with some of the control point data he gave me.
> > So 
> > I am wondering if I maybe did something wrong in my code. Here is the
> > 
> > code I used:
> > 
> > PJ *prjState = pj_init_plus("+proj=lcc +lat_0=43 +lon_0=-94 
> > +lat_1=45.21666666666666666666666666666666666 
> > +lat_2=43.783333333333333333333333 +x_0=800000 +y_0=100000
> > +ellps=GRS80 
> > +datum=NAD83 +units=ft +no_defs");
> > PJ *prjWGS = pj_init_plus("+proj=latlong +ellps=WGS84 +datum=WGS84");
> > 
> > double x[1], y[1], z[1];
> > int err;
> > 
> > x[0] = -93.242251388888888888888888888889 * DEG_TO_RAD;
> > y[0] = 44.887752777777777777777777777778 * DEG_TO_RAD;
> > z[0] = 0.0;
> > 
> > err = pj_transform(prjWGS, prjState, 1, 1, x, y, z);
> > 
> > With this code and for the lat/lon values listed in the code, I get
> > the 
> > following State Plane coordinates returned: 2821057.917382
> > 1017161.112401
> > 
> > While the reference data says it should be: 2821052.29398607, 
> > 1017159.04559559
> > 
> > As you can see the difference is a few feet. Can anybody tell me if I
> > 
> > have done something wrong in my code, or should I doubt the quality
> > of 
> > the reference data :)?
> > 
> > Thanks,
> > 
> > Arno
> > _______________________________________________
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> > Proj at lists.maptools.org
> > http://lists.maptools.org/mailman/listinfo/proj
> > 
> 
> 
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