[Proj] Problems with EOV for Hungary (1972 Egyseges OrszagosVetuleti)

[OvV_HN]

----- Original Message ----- 
From: "Roger Oberholtzer" <roger at opq.se>
To: <proj at lists.maptools.org>
Sent: Tuesday, September 22, 2009 11:02 AM
Subject: [Proj] Problems with EOV for Hungary (1972 Egyseges 
OrszagosVetuleti)


>I am trying to use proj (C API) to project WGS84 lat/longs in EOV for
> Hungary (1972 Egyseges Orszagos Vetuleti). I am trying to match some
> user data. The are using ArcGis with the following definition:
>
>        PROJCS["HD_1972_Egyseges_Orszagos_Vetuleti",
>        GEOGCS["GCS_Hungarian_1972",
>        DATUM["D_Hungarian_1972",
>        SPHEROID["GRS_1967",6378160,298.247167427]],
>        PRIMEM["Greenwich",0],
>        UNIT["Degree",0.0174532925199432955]],
>        PROJECTION["Hotine_Oblique_Mercator_Azimuth_Center"],
>        PARAMETER["False_Easting",650000],
>        PARAMETER["False_Northing",200000],
>        PARAMETER["Scale_Factor",0.99993],
>        PARAMETER["Azimuth",90],
>        PARAMETER["Longitude_Of_Center",19.048571778],
>        PARAMETER["Latitude_Of_Center",47.14439372222],
>        UNIT["Meter",1]]
>
> I have set this up as:
>
>   from = pj_init_plus(
>                "+proj=latlong "
>                "+ellps=WGS84");
>
>   to = pj_init_plus(
>                "+proj=somerc "
>                "+lat_0=47.14439372222222 "
>                "+lon_0=19.04857177777778 "
>                "+k=0.99993 "
>                "+x_0=650000 "
>                "+y_0=200000 "
>                "+ellps=GRS67 "
>                "+units=m "
>                "+no_defs");
>
>     pj_transform(to, from, 1, 0, &le, &ln, &la);
>
> When I run some test data, I am always 80 some meters away. For example:
>
>   Ref:    Latitude:   47.7656110000 Longitude:   18.9532900000
>   Ref:    Easting:       642942.000 Northing:       269097.700
>   Calc:   Easting:       642857.473 Northing:       269067.872


By the way, a Hotine_Oblique_Mercator_Azimuth_Center is not the same as 
somerc, the Swiss oblique Mercator projection. But, somerc is a better 
approximation for EOV than a Hotine omerc.

Anyhow, with the datum transformation parameters from Mikael Rittri and a 
coordinate frame rotation, I got with:
Ref:    Latitude:   47.7656110000 Longitude:   18.9532900000
a latitude, longitude of 47.765881, 18.954420
and with an accurate implementation of the EOV projection an (original axes) 
x, y of:
269097.773, 642942.210
which is, let's say, spot on.
The approximation with somerc should give (its) x, y of:
642942.210, 269097.775


Oscar van Vlijmen