[Proj] Michigan Georef projection support?

[Oscar van Vlijmen]

From: "Clever, Max" <Maxc-spicergroup.com>
Date: Thu, 20 Jul 2006 10:23:22 -0400
Subject: [Proj] Michigan Georef projection support?

> I've read a few posts and it looks like Gerald has already developed support
> for RSO's.  In the previous emails shown below, I have code written for Hotine
> Oblique Mercators that uses the Michigan Georef Parameters. Hopefully the code
> you have written is more accurate.  I could not get the Northing accurate
> enough.  If you want the parameters for Michigan Georef they are available
> online if you google "Michigan Georef Projection".

I still haven't seen any (near) official test points (lat,lon to x,y) for
Michigan GeoRef. Not in the maptools postings, not on the internet.
If nobody will produce some serious test points, no problem can be
diagnosed.

The test points M. Kennedy gave on 2004-12-20 in a posting can be understood
as follows.
The parameters are for my code, a slightly improved version of libproj4's
omerc with additions from the EPSG/OGP Guidance Note.

lat = 43; lon = -86;
// GRS80 ellipsoid
type = 5; // Hotine-RSO according to EPSG
lat0 = 45.30916666667; // latitude of projection's origin: 45d18m33s N
lonc = -86; // longitude of projection's origin: 86d00m00s W
alfac = 337.255555555556; // azimuth at center of projection: 337d15m20s
gamma = ""; // let the code calculate gamma
k0 = 0.9996; // scale factor at projection's center
x0 = 2546731.496; // false easting
y0 = -4354009.816; // false northing
norot = 0; no_off = 0;
omerc(type,lat,lon,lat0,lonc,alfac,gamma,k0,x0,y0,norot,no_off)
Result: x,y = 499864.500077, 272108.859263

Some people get mighty nervous seeing all those decimals, but for testing
purposes they are necessary.

M. Kennedy, 2004-12-20:
"
and now the results from the ESRI Projection Engine
cymru{melita}: forward91 102123
Projection Engine Version 9.0 (Dec 15 2004)
499864.50  272108.86
"

And now for something completely different:
(only the differences with above are mentioned):

type = 1; // comparable with libproj4 omerc or the USA-type 'Hotine'
no_off = 1;
Result: 499864.500077, 272108.859263

As long as no official test points are available I would suggest:
Do the MI GeoRef with (lib)proj omerc and the no_offset flag set.