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

Rick Graves gravesricharde at yahoo.com
Mon Jul 23 08:57:08 EST 2012

```Gabor,

> But then I changed the order of coordinates, so longitude first, latitude second...

That was my mistake!  When I put longitude first, latitude second, I also get sensible numbers.

So proj wants "x, y", not "latitude, longitude", even when you are feeding it latitude, longitude.

I should have caught that.

Sorry for the trouble!

Thanks,

Rick

________________________________
From: "molnar at sas.elte.hu" <molnar at sas.elte.hu>
To: Rick Graves <gravesricharde at yahoo.com>; PROJ.4 and general Projections Discussions <proj at lists.maptools.org>
Sent: Monday, July 23, 2012 3:59 AM
Subject: Re: [Proj] does proj.4 work with Hotine Oblique Mercator?

Hi Rick!

First I also got very similar results as you (using the +no_uoff parameter).
But then I changed the order of coordinates, so longitude first, latitude
second...
It seems to be in the bounding box, but i have not checked it in detail.
Good luck,

Gabor Molnar

C:\Program Files\#######\>proj -v +proj=omerc +lat_0=45.30916666666666
+lonc=-86 +alpha=337.25556 +k_0=0.9996 +x_0=2546731.496 +y_0=-4354009.816
+no_uoff
#Oblique Mercator
#       Cyl, Sph&Ell
#        no_rot rot_conv no_uoff and
#       alpha= lonc= or
#        lon_1= lat_1= lon_2= lat_2=
# +proj=omerc +lat_0=45.30916666666666 +lonc=-86 +alpha=337.25556 +k_0=0.9996
# +x_0=2546731.496 +y_0=-4354009.816 +no_uoff +ellps=WGS84
45 -86
-10249168.62    22654031.15
42d15n 83d45w
-9992196.95     22682402.40
83d45w 42d15n
685493.47       191370.74

> 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.
>
>     +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).
>
>
> (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
>>
>>
>>
>> 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:
>>
>>
>>    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]]
>>
>>
>>
>>
>>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:
>>
>>
>>
>>
>>
>>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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