Re: Low latitude RTP / RTE transformation

Hi Joaquim,
 
That's useful to know. Yes the RTP is problematic at low latitudes, which does make it tricky knowing how to work the data.
 
There is a free sofware by Markku Pirttijarvi called Fourpot (v1.3) that does both th classic RTP and RTE as well as the various derivatives, but does take some getting used to the inputs etc:
 
http://www.cc.oulu.fi/~mpi/Softat/Fourpot.html
 
I guess that as long as we are looking at areas +/-15 deg grdredpol should be able to handle things.
 
Did come across an article that discusses a modified RTP and RTE method, although it would need someone that understands the methodology to assess the validity of the equations:
LUO Yao, XUE Dian-Jun, WANG Ming (2010), Reduction to the pole at the geomagnetic equator. 
CHINESE JOURNAL OF GEOPHYSICS Vol.53, No.6, 2010, pp: 1082-1089
 
 
Cheers
Lester

 
Date: Fri, 28 Feb 2014 12:18:58 +0000
From: [email protected]
Subject: Re: [GMT-HELP] Low latitude RTP / RTE transformation
To: [email protected]


  
    
  
  
    Lester,

    

    Its is well known that the Reduction-To-Pole operators simply do not
    work at low latitudes (~10-15 deg) and the problem of an RTE is also
    harder than the RTP.

    For cases like this, or others like for instances the interpolation
    with break lines, it is normally necessary that one of the
    developers has a personal interest in the problem so that the result
    ends up in GMT. That was what happened with grdredpol and it may
    happen again, but in an uncertain future.

    However, things could go much faster if someone had open source code
    to contribute (but not GPL'de one).

    

    Joaquim

    

    
      
      Hello,

         

        With GMT5 we now have a proper RTP transform tool
        (GRDREDPOL) for performing both the classic (constant field
        vector) and differential (variable field vector) for working on
        large areas. However, RTP at low latitudes is unstable and the
        results are skewed.

         

        Would it be feasible to include either a low-latitude correction
        for the RTP and/or a separate "Reduce-to-Equator RTE" program?

         

        Cheers

        Lester

      
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