[Proj] does proj.4 work with Hotine Oblique Mercator?

[Rick Graves]

Mikael,

When I add the +no_uoff parameter, I get different numbers for Ann Arbor Michigan:

-9992196.95     22682402.40


They are also out of bounds -- all 4 bounding box numbers have 6 figures to the left of the decimal point.  I am assuming that the Michigan shapefile is OK.  The difference between the bounding box limits is approximately 600-700 km, which seems correct (I measured a road atlas using a long ruler).

The figures I got using the no_uoff parameter are more than 6 figures to the left of the decimal point.

The gamma parameter makes no difference with the no_uoff parameter.  The gamma parameter without the no_uoff parameter gives different numbers for Ann Arbor:

-7945305.71     17799792.28


Still out of bounds.

I have proj Rel. 4.7.1, 23 September 2009 (came with ubuntu Linux 12.04).

Am I making some mistake, or does proj.4 not work with Hotine Oblique Mercator?

Thanks,


Rick


________________________________
 From: Mikael Rittri <Mikael.Rittri at carmenta.com>
To: Rick Graves <gravesricharde at yahoo.com>; PROJ.4 and generalProjections Discussions <proj at lists.maptools.org> 
Cc: "proj at lists.maptools.org" <proj at lists.maptools.org> 
Sent: Sunday, July 22, 2012 12:21 PM
Subject: Re: [Proj] does proj.4 work with Hotine Oblique Mercator?
 

Hello Rick.
You need to add 

    +no_uoff

to your Proj.4 definition. This is just a flag, so it doesn't need any numerical value.
But it must be included so that you get what EPSG calls "Hotine Oblique Mercator Variant A".
Without it, you get the Variant B instead. One could say that the Hotine Oblique Mercator class has two
distinct construction methods (for historical reasons), and the GIS community hasn't been able
to agree to use only one. 

The names Variant A and B are fairly recent EPSG names. In WKT etc., other names for the 
variants appear (usually different for different WKT dialects).

See also http://trac.osgeo.org/proj/ticket/104

(Possibly, with Proj 4.8.0 you should also add

    +gamma=337.25556

for the rectified grid angle, but I think an omitted gamma defaults to the given alpha value,
so an explicit gamma is probably unnecessary in your case.)

Best regards,

Mikael Rittri
Carmenta
Sweden
http://www.carmenta.com

22 jul 2012 kl. 18:42 skrev "Rick Graves" <gravesricharde at yahoo.com>:


Hey,
>
>
>I am not sure that proj.4 is converting latitude and longitude into Hotine Oblique Mercator coordinates correctly.  (But I am a newbie at cartography and such, so please bear with me, I could be making a mistake.)
>
>
>As a result of the 2010 census in the USA, many states have redrawn their congressional districts.  Michigan is one, and the shapefiles for their new districts were created using the Hotine Oblique Mercator projection to get the whole state onto one map with a minimum of overall distortion.  There is a map and explanation here:
>
>
>http://www.michigan.gov/documents/DNR_Map_Proj_and_MI_Georef_Info_20889_7.pdf
>
>
>
>One can download Michigan's new Congressional district shapefiles from here:
>
>
>http://www.mcgi.state.mi.us/mgdl/?rel=thext&action=thmname&cid=9&cat=Legislative+Districts+2010+US+Congress
>
>
>
>The included prj file has this info:
>
>
>PROJCS["NAD83 / Michigan Oblique Mercator",
>GEOGCS["NAD83",
>    DATUM["North_American_Datum_1983",
>SPHEROID["GRS 1980",6378137,298.257222101,
>    AUTHORITY["EPSG","7019"]],
>AUTHORITY["EPSG","6269"]],
>    PRIMEM["Greenwich",0,
>AUTHORITY["EPSG","8901"]],
>    UNIT["degree",0.01745329251994328,
>AUTHORITY["EPSG","9122"]],
>    AUTHORITY["EPSG","4269"]],
>UNIT["metre",1,
>    AUTHORITY["EPSG","9001"]],
>PROJECTION["Hotine_Oblique_Mercator"],
>PARAMETER["latitude_of_center",45.30916666666666],
>PARAMETER["longitude_of_center",-86],
>PARAMETER["azimuth",337.25556],
>PARAMETER["rectified_grid_angle",337.25556],
>PARAMETER["scale_factor",0.9996],
>PARAMETER["false_easting",2546731.496],
>PARAMETER["false_northing",-4354009.816],
>AUTHORITY["EPSG","3078"],
>AXIS["X",EAST],
>AXIS["Y",NORTH]]
>
>
>This page has info on the Hotine Oblique Mercator:
>
>
>http://www.remotesensing.org/geotiff/proj_list/hotine_oblique_mercator.html
>
>
>
>Using that, I came up with this command to invoke proj:
>
>
>proj +proj=omerc +lat_0=45.30916666666666 +lonc=-86 +alpha=337.25556 +k_0=0.9996 +x_0=2546731.496 +y_0=-4354009.816
>
>
>I get a latitude and longitude for Ann Arbor Michigan of 42 15 N - 83 45 W here:
>
>
>http://wiki.answers.com/Q/What_is_the_latitude_and_longitude_of_ann_arbor_mi
>
>
>
>Plugging 42d15N 83d45W into proj, I get -7945305.71 17799792.28.  But the bounding box of the entire state's shape file is this:
>
>
>161318.17712499946, 128066.04250000045, 791832.2827499993, 859206.8181249984
>
>
>
>The values I get from proj are both out of bounds. 
>
>
>Am I doing something wrong?
>
>
>Thanks,
>
>
>Rick Graves
>
>
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