[OSRS-PROJ] FW: Datum shiffting problem

[Frank Warmerdam]

Igor Alfirevic wrote:
>  
> 
> 
> Hi there!
> 
> 
> I have the following paramters(custom datum):
> 
> major semiaxis +a=6378388
> Flattening     +es=0.00336700336700273
> 
> Shift          dX=-87
>                dY=-98
>                dZ=-121
> 
> and i try to convert lat/long coordinates to utm coordinates.
> 
> I was trying to convert with cs2cs program:
> 
> cs2cs +proj=latlong +datum=WGS84 +to +proj=utm +a=6378388
> +es=0.00336700336700273 +zone=33 +towgs84=-87,-98,-121
> 
> and as input i use
> 
> 13d57'10.9"E 46d05'55.3"N
> and as result i received
> 
> 419076.12   5107361.73
> 
> But i shuld receive:
> 419071      5105641
> 
> I read lat/lon coordinates on ellipsoid with same parameters:

Igor,

I did a few quick checks, and it appears that the steps in the process
(ellipsoid conversion and datum shifting) are both being applied.  Are
you sure your expected results represent what this transformation is
supposed to do?  Note that 3 parameter datum shifts are typically not very
good approximations of datum differences over large areas.

I guess my main point is that I can't isolate any obvious problems in the
calculations being done by cs2cs.

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/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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