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

Sun Jul 22 10:45:05 PDT 2012

I have not looked at your macro in detail other than to comment that I thought the Michigan RSO used a different value for the semi-major axis of the ellipsoid in order to take into account the average elevation of the State.  I see you are using GRS80 exactly, which may be your problem.

Clifford J. Mugnier, c.p., c.m.s.

Chief of Geodesy

LSU Center for GeoInformatics (ERAD 266)

Dept. of Civil Engineering (P.F. Taylor 3531)

LOUISIANA STATE UNIVERSITY

Baton Rouge, LA  70803

Academic: (225) 578-8536

Research: (225) 578-4578

Cell:             (225) 328-8975

honorary lifetime member, lsps

fellow emeritus, asprs

member, apsg

________________________________
From: proj-bounces at lists.maptools.org [proj-bounces at lists.maptools.org] on behalf of Rick Graves [gravesricharde at yahoo.com]
Sent: Sunday, July 22, 2012 11:41 AM
To: proj at lists.maptools.org
Subject: [Proj] does proj.4 work with Hotine Oblique Mercator?

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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