[OSRS-PROJ] Re: Proj.4 DLL ?

[Frank Warmerdam]

Bart Adriaanse wrote:
> 
> Hi Frank,
> 
> I did some testing using the proj.exe command line mode.
> 
> The Dutch projection works absolutely perfect with the parameters you
> suggested, only the datum shift parameters seem to be ignored on the
> command line.
> 
> The fact that it does the projection so nicely made us decide to drop
> other alternatives like GCTP and Geotrans and use PROJ.4 for our
> projects from now on.
> I suppose we will get the datum shift to work somehow, maybe with a
> little advice from you.
> 
> Whatever improvements we might make on the code itself we will surely
> feed back to you, but the idea is to use the DLL "as is" without any
> modifications.
> 
> Thanks a lot for your support sofar !

Bart, 

Sorry about the datum this, my fault. 

The proj.exe program itself doesn't include datum shifting support.  I wrote
a similar mainline program called cs2cs (coordinate system to coordinate 
system) which internally calls the pj_transform() function as opposed to
the simple LL<->proj functions pj_fwd() and pj_inv().  

In short, I think you should be able to do something like:

cs2cs +proj=stere +lat_0=52.1561605555555 +lon_0=5.38763888888888 +k=0.9999079
            +x_0=155000 +y_0=463000 
            +towgs84=593.16,26.15,478.54,-6.3239,-0.5008,-5.5487,4.077 
            +ellps=bessel
      +to +proj=latlong +datum=WGS84

This would translated between the dutch projection and latlong coordinates 
in WGS84.  To do the reverse:

cs2cs +proj=latlong +datum=WGS84
      +to +proj=stere +lat_0=52.1561605555555 +lon_0=5.38763888888888 +k=0.9999079
            +x_0=155000 +y_0=463000 
            +towgs84=593.16,26.15,478.54,-6.3239,-0.5008,-5.5487,4.077 
            +ellps=bessel
      
I hope to better document the datum support, cs2cs, and pj_transform() in the
next release of PROJ.4.  

All credit for the quality of transformations in PROJ.4 goes of course to 
Gerald Evenden who wrote it.

Best regards,

---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerda
and watch the world go round - Rush    | Geospatial Programmer for Rent
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