[Proj] RE: The Michigan Georef Projection Problem
Maxc at spicergroup.com
Tue Dec 21 11:00:44 EST 2004
I have, since last friday, collected the coordinates of a couple of points on a subject shapefile that I am using in my mapfile. I obtained the coordinates for the same 2 points in multiple projections on the map file. Here are my results:
the true x,y coordinates in Georef for point 1 and 2 are (637710.1274,308893.2468) and (591416.4708,310783.3271) respectively. The azimuth from 1 to 2 in D-M-S.ss is 272-20-16.7177 and the distance is 46332.22469 meters.
The state plane coordinates I used were made by projecting the above georef shapefile using Arc3.2 with the Michigan DNR projection extention. The last time I checked it, could return the same coordinates as the original georef file when reprojecting the state plane coordinates that were projected from georef to less than 0.0001 of a meter. The "correct" State Plane South Zone Coordinates for points 1 and 2 in US feet are (13141120.4489,662643.9213) and (12989341.0501,671851.6545) respectively. The azimuth between from 1 to 2 in D-M-S.ss is 273-28-17.7866 and the distance is 152058.437 feet.
When the shapefile containing this correct state plane data is assigned an EPSG of 102690 (State Plane South US ft) and the mapfile is assigned an EPSG of 102123 (Michigan Georef Meters) the coordinates are (2684601.3710,-4573716.8730) and (2638307.7140,-4571826.7920). The azimuth between from 1 to 2 in D-M-S.ss is 272-20-16.7208 and the distance is 46332.2251 meters. These coordinates are very similar in location to the false easting and northing of the Michigan Georef Projection. So it seems to be creating coordinates too small before application of the false easting and northing. This is the problem that happens when going from ellipsoid to georef.
The problem of going from georef to ellipsoid seems to be a whole other animal. When I used the shapefile that was in the correct Georef coordinates and viewed it in a mapfile defined as Michigan state plane south zone US feet, its projected coordinates for point 1 and 2 were (4371120.1277,17653814.8435) and (4191630.5827,17599163.9607) respectively. The azimuth between from 1 to 2 in D-M-S.ss is 253-03-56.1010 and the distance is 187625.2002 feet. Going from Georef to ellipsoid doesn't matter as much to me since my mapfile is meant to be defined as Michigan Georef, but this is still a problem that ought to be looked into.
Just so everyone knows, UTM to LCC and vice versa have both worked fine, even data in UTM shows up in the same wrong spot as the state plane data when the mapfile is in Georef. So I don't see any possible way that the State Plane definitions could be part of the problem.
I'm just putting this info out there for anybody that might know how to solve it.
From: Melita Kennedy [mailto:mkennedy2 at earthlink.net]
Sent: Saturday, December 18, 2004 3:07 PM
To: proj at xserve.flids.com
Cc: Clever, Max
Subject: Re: The Michigan Georef Projection Problem
Can you give some details on what the problems are? Obviously, you aren't
getting the results you expect but would you post some samples and what
your expected results are? Can you narrow down the problem to Michigan
GeoRef to lat/lon? Does it look like you can project to Michigan GeoRef
If you would, please cc any information to my work account, mkennedy AT
esri.com. I'll be in the office on Monday, but won't be able to do any
tests after that until the 29th or so.
And my home account (where I receive this list is changing to mkennedy2 AT
earthlink.net. I think I have my subscription address changed correctly!
> On Sat, 18 Dec 2004 12:00:05 -0500 (EST), you wrote:
> Message: 1
> Date: Fri, 17 Dec 2004 16:09:08 -0500
> From: "Clever, Max" <Maxc at spicergroup.com>
> Subject: [Proj] The Michigan Georef Projection Problem
> To: <proj at xserve.flids.com>
> Cc: mkennedy at pe.net
> I have run into problems with the Michigan Georef projection and I think I have read all
> the threads on it, which did not end up coming up with a solution. Have there been any
> fixes for this projection? If not, then I might need to work on Proj, which is a bit scary,
> but I still have the code of a VB program I wrote that performs the transformation for
> michigan georef to state plane and vice versa. But, before I delve into Proj's code, I
> just wanted to check on this listing if anybody has solved the problem.
> Until then, I will hope for the best.
> Happy Holidays
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