Hello Everyone, Two years ago, I ran into a problem with the Michigan Georef Projection and the way that proj identified it. I had sent emails back and forth for a while until someone sent a temporary solution of providing false parameters that worked.. for the most part. Thistemporary solution, of course, did not actually solve the problem, but instead delayed the fixing of the methods that proj identifies projections and translates them. For that I am sorry for not remaining vigilant in seeing a true solution being devised. But now, since I have just now installed the latest version of GRASS 6.1, I have come full circle and face this problem again. To provide a quick access to the background of what has already been said on this projection please note the previous emails below. I believe, at this time still, that the omerc projection and its parameters as used by proj cannot correctly describe or transform a omerc projection with a "natural origin". From what I understand, Hotine oblique mercator and Rectified Skew Orthomorphic are one and the same or depend on where the skew is corrected. Has there been a solution determined for this projection? If not, maybe a solution to this problem would be to have Proj have oblique mercators split between "natural origins" and cartesian center point origins. I hope, maybe, someone has been looking at this lately but I doubt it. Any comments or solutions would be very welcome. Thanks.
Max Clever Gerald Evenden gerald.evenden at verizon.net <mailto:proj%40lists.maptools.org?Subject=%5BFwd%3A%20Re%3A%20%5BProj%5D%20Re%3A%20The%20Michigan%20Georef%20Projection%20Problem%5D&In-Reply-To=> Wed Dec 22 16:00:32 EST 2004 * Previous message: [Fwd: Re: [Proj] Re: The Michigan Georef Projection Problem] <http://lists.maptools.org/pipermail/proj/2004-December/001440.html> * Next message: [Proj] A problem with this list <http://lists.maptools.org/pipermail/proj/2004-December/001442.html> * Messages sorted by: [ date ] <http://lists.maptools.org/pipermail/proj/2004-December/date.html#1441> [ thread ] <http://lists.maptools.org/pipermail/proj/2004-December/thread.html#1441> [ subject ] <http://lists.maptools.org/pipermail/proj/2004-December/subject.html#1441> [ author ] <http://lists.maptools.org/pipermail/proj/2004-December/author.html#1441> _____ Just to add my own two cents: the biggest problem with omerc is that there are no universal standards for specifying this projection. Indeed, Hotine may have had a specific method in mind but various uses have created their own systems and that's why there is 4 pages of description on the projection in the file omerc.pdf on: http://members.verizon.net/~vze2hc4d/proj4/ <http://members.verizon.net/%7Evze2hc4d/proj4/> This applies to libproj4 but some applies to old proj4. _____________________________________ Jerry and the low riders: Daisy Mae and Joshua. "The whole religious complexion of the modern world is due to the absence from Jerusalem of a lunatic asylum." Havelock Ellis, 1914 Max - Thanks; I guess my concern is that it would be odd for proj to "misuse" this particular set of false easting and northing values, since it is known to correctly use such values in all sorts of cases. I just don't like accepting answers that appear to work "for whatever reason", and I will try to find time to look into this. I'm reminded of the last two chapters of Isaac Asimov's "Second Foundation". They're titled "The Answer that Satisfied", followed by "The Answer that was True"! - Ed Ed McNierney President and Chief Mapmaker TopoZone.com / Maps a la carte, Inc. 73 Princeton Street, Suite 305 North Chelmsford, MA 01863 Phone: +1 978 251-4242 Fax: +1 978 251-1396 -----Original Message----- From: Clever, Max [mailto:Maxc at spicergroup.com <http://lists.maptools.org/mailman/listinfo/proj> ] Sent: Wednesday, December 22, 2004 1:21 PM To: Ed McNierney Cc: proj at xserve.flids.com <http://lists.maptools.org/mailman/listinfo/proj> Subject: RE: [Fwd: Re: [Proj] Re: The Michigan Georef Projection Problem] 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 <http://lists.maptools.org/mailman/listinfo/proj> ] 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 <http://lists.maptools.org/mailman/listinfo/proj> ] 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 <http://lists.maptools.org/mailman/listinfo/proj> > Reply-To: Melita Kennedy [ESRI-Redlands] <mkennedy at esri.com <http://lists.maptools.org/mailman/listinfo/proj> > To: gerald.evenden at verizon.net <http://lists.maptools.org/mailman/listinfo/proj> , mkennedy2 at earthlink.net <http://lists.maptools.org/mailman/listinfo/proj> , <http://lists.maptools.org/mailman/listinfo/proj> keon at nacse.org <http://lists.maptools.org/mailman/listinfo/proj> CC: mkennedy at esri.com <http://lists.maptools.org/mailman/listinfo/proj> 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 <http://lists.maptools.org/mailman/listinfo/proj> -----Original Message----- From: Ed McNierney [mailto:ed at topozone.com <http://lists.maptools.org/mailman/listinfo/proj> ] Sent: Tuesday, December 21, 2004 1:20 PM To: Clever, Max; proj at xserve.flids.com <http://lists.maptools.org/mailman/listinfo/proj> 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 <http://lists.maptools.org/mailman/listinfo/proj> (978) 251-4242 -----Original Message----- From: proj-bounces at xserve.flids.com <http://lists.maptools.org/mailman/listinfo/proj> [mailto:proj-bounces at xserve.flids.com <http://lists.maptools.org/mailman/listinfo/proj> ] On Behalf Of Clever, Max Sent: Tuesday, December 21, 2004 1:23 PM To: proj at xserve.flids.com <http://lists.maptools.org/mailman/listinfo/proj> 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
