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

[Mikael Rittri]

Jean-Claude wrote:
>
> Roger Oberholtzer wrote:
> > - - -
> > When I run some test data, I am always 80 some meters away.
>
> 
> You are missing the +towgs84 parameter, which is necessary
> if you want PROJ.4 to perform a datum change.

Yes. I looked at www.epsg-registry.org, and searched on

   Type: Coordinate Transformation
   Area: Hungary

This gave a couple of 3-parameter and 7-parameter transforms
for HD72.  As usual, some of them were informally deprecated
in the comments field, but not formally DEPRECATED in the
technical sense.  Anyway, the best one seems to be 

    EPSG:1448 "HD72 to WGS 84 (3)"

which has the same parameters as 

    EPSG:1449 "HD72 to ETRS89 (2)",

namely 
    
    X-axis translation   52.684   metre      
    Y-axis translation   -71.194  metre   
    Z-axis translation   -13.975  metre   
    X-axis rotation   0.312   arc-second  
    Y-axis rotation   0.1063  arc-second  
    Z-axis rotation   0.3729  arc-second  
    Scale difference  1.0191  parts per million  

However, there is a warning _above_ these parameters: 

   "Care! Ensure application uses this method! See Guidance Note 7-1"

which means that you must scroll _down_ to the bottom line, where you find

   +Method [Coordinate Frame rotation]

and, since PROJ.4 uses the opposite sign convention for the rotation
angles (the Position Vector Transform), these angles must be negated.  
So, I think you should use

   +towgs84=52.684,-71.194,-13.975,-0.312,-0.1063,-0.3729,1.0191

to implement HD72. 

Best regards,
--
Mikael Rittri
Carmenta AB
Göteborg
SWEDEN
www.carmenta.com

-----Original Message-----
From: proj-bounces at lists.maptools.org [mailto:proj-bounces at lists.maptools.org] On Behalf Of Jean-Claude REPETTO
Sent: den 22 september 2009 11:57
To: PROJ.4 and general Projections Discussions; roger at opq.se
Subject: Re: [Proj] Problems with EOV for Hungary (1972 Egyseges Orszagos Vetuleti)

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