[Fwd: Re: [Proj] Re: The Michigan Georef Projection Problem]

Wed Dec 22 13:21:16 EST 2004

Ed,

the False Northings and Eastings defined in the Original Michigan Georef EPSG file are the true parameters, but Proj does not handle them properly for whatever reason.  The new Northings and Eastings that Melita provided make up for Proj's miscalculation, at least to a certain degree.  The problems that proj had originally created SEEM to me to only be of a translational manner, other characteristics such as azimuths and distances were very close to what they should be.  However, I have not looked at the code that Proj uses for this projection.  So, all in all, I guess I would say that the problem with proj and this EPSG 102123 is not really fixed.  But the new false Northing and Eastings that Melita provided will work for what I intend to do for now.  I don't consider myself an expert on transformation algorithms, even though I've written a few before.  All I know is what the epsg parameters stand for and that in this case, proj seems to be misusing them.

Max Clever

-----Original Message-----
From: Ed McNierney [mailto:ed at topozone.com]
Sent: Tuesday, December 21, 2004 7:04 PM
To: Clever, Max
Subject: RE: [Fwd: Re: [Proj] Re: The Michigan Georef Projection
Problem]

Max -

Yes, I saw that message - it just wasn't obvious what her changes were.
So you're saying that the False Northing and False Easting values are
incorrect, and that's it?  So now we have to figure out WHY they're
incorrect.  The values shown below:

 +x_0=2546731.496 +y_0=-4354009.816
 +x_0=499839.8337 +y_0=528600.2398

look completely different from one another.  Why?  I'm very concerned
that if you don't really understand why this change "fixed" the problem,
then it might not really fix it in the general case.

	- Ed

-----Original Message-----
From: Clever, Max [mailto:Maxc at spicergroup.com] 
Sent: Tuesday, December 21, 2004 5:40 PM
To: Ed McNierney
Subject: RE: [Fwd: Re: [Proj] Re: The Michigan Georef Projection
Problem]

Ed,

this is the message that Dylan forwarded me today.  It solved my problem
of trying to project data with UTM and Michigan State Plane coordinates
onto a mapfile defined with the Michigan Georef Projection.  It gets the
image within about 0.5 meters of where it ought to be I think.  Here's
the message containing the parameters.  Really the only thing that ought
to be changed is the False Easting and False Northing, she rounded the
latitude and longitude to not enough decimal places but if you use what
she shows for that then its pretty close. 

-------- Original Message --------
Subject: Re: [Proj] Re: The Michigan Georef Projection Problem
Date: Mon, 20 Dec 2004 12:39:54 -0800 (PST)
From: Melita Kennedy [ESRI-Redlands] <mkennedy at esri.com>
Reply-To: Melita Kennedy [ESRI-Redlands] <mkennedy at esri.com>
To: gerald.evenden at verizon.net, mkennedy2 at earthlink.net, keon at nacse.org
CC: mkennedy at esri.com

Hi Dylan, Jerry, and Frank

I'm not cc'ing to the list as I don't think I can post from this e-mail
account. Dylan, feel free to post all or part of my reply on the list if
you wish.

I think I understand what's happening, although I'm bit confused because
it means that the State Plane zone, Alaska zone 1, probably isn't
working either.

First off, here are a few test points from PROJ using this defn.

proj +proj=omerc +lat_0=45.309166667 +lonc=-86.0 +alpha=337.255555556
+k=0.9996 +x_0=2546731.496 +y_0=-4354009.816 +ellps=GRS80 +datum=NAD83 
+units=m

86W 43N
2546756.16 -4610501.20
86W 44N
2626908.90 -4498940.28
86W 45.309166667N
0.00 0.00

and now the results from the ESRI Projection Engine

cymru{melita}: forward91 102123
Projection Engine Version 9.0 (Dec 15 2004)
-86 43
-85 44
-86 45.309166667
499864.50  272108.86
580017.24  383669.77
499839.83  528600.24

Quite a difference, eh?

Hotine, "Oblique Mercator", RSO, and whatever other names are in use
confused me for quite a while. The ESRI Projection Engine now has
6 variants to try to support this map projection. Partially, that's
because we've added different versions at different times as we've come
to understand the projection better.

Hotine 2 Pt Natural Origin
Hotine 2 Point Center
Hotine Azimuth Natural Origin
Hotine Azimuth Center

Rectified Skew Orthomorphic - Natural Origin Rectified Skew Orthomorphic
- Center

PROJ supports Two Point and Point/Azimuth cases. From what I'm seeing in
the results and in the documentation, they are what ESRI calls the
'Center' cases. That is, the cartesian origin is located at the 'center'
of the projection, lonc and lat_0.

The ESRI Natural Origin cases have the cartesian origin where the
central line crosses the aposphere. This is almost the ellipsoid's
equator. Alaska zone 1 and Michigan GeoRef both use the natural origin
case of Point/Azimuth. That's why they have such large negative false
northings and large positive false eastings.

The ESRI version (and the PROJ versions) also rectify the projection
back to 'north'. The default proj setting is +no_rot (no rotation).
The azimuth is used for the rectifying angle.

Hmmm, I get different results if I use +no_rot versus when I omit it. So
perhaps +no_rot is a rectifying angle of zero.

The ESRI RSO implementation have the same Hotine parameters, plus a
rectifying angle. Although I haven't tested it, I believe this is the
same parameter as the +no_rot parameter. The standard RSO definitions
must have this parameter set, as the rectifying angle is not the same as
the azimuth.

Snyder talks somewhat about this in a footnote in _Map Projections:
A Working Manual_, but I (and the projection programmers here find the
entire section to be difficult to follow.

I think you can get the results you expect with these parameters:

proj +proj=omerc +lat_0=45.309166667 +lonc=-86.0 +alpha=337.255555556
+k=0.9996 +x_0=499839.8337 +y_0=528600.2398 +ellps=GRS80 +datum=NAD83 
+units=m

Melita

--
Melita Kennedy
Product Specialist
ESRI, Inc.
mkennedy at esri.com

-----Original Message-----
From: Ed McNierney [mailto:ed at topozone.com]
Sent: Tuesday, December 21, 2004 1:20 PM
To: Clever, Max; proj at xserve.flids.com
Subject: RE: [Fwd: Re: [Proj] Re: The Michigan Georef Projection
Problem]

Max -

I didn't have time to closely read Melita's email - what exactly was the
correction?  If the EPSG parameters for this projection are incorrect,
we should get that reported and fixed.  Thanks!

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
ed at topozone.com
(978) 251-4242  

-----Original Message-----
From: proj-bounces at xserve.flids.com
[mailto:proj-bounces at xserve.flids.com] On Behalf Of Clever, Max
Sent: Tuesday, December 21, 2004 1:23 PM
To: proj at xserve.flids.com
Subject: RE: [Fwd: Re: [Proj] Re: The Michigan Georef Projection
Problem]

Hello Everyone,

I just wanted to say thanks to everybody for the fix of the EPSG.
Melita, those new translational parameters worked great for what we are
doing with Michigan Georef, thanks to everyone who put time into
figuring out what was going wrong.  This forum definitely has some
collective brainpower.

Happy Holidays Everyone

Max Clever
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