[Proj] WGS84 to Minnesota State Plane South

[Eric Miller]

It's probably the difference between the international foot "ft" and the US Survey foot "us_ft".  There's a lot of confusion about this with the state plane coordinate systems.  I think it's pretty universal that the NAD27 variants are all "us_ft", but when the NAD83 variants were adopted, they were all supposed to use meters.  However, different states and jurisdictions did different things and you'll see all three units used (meters, us_ft and ft).

>>> On 1/3/2008 at 1:03 AM, 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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