[PROJ] Confusion using cct with helmert transformation.

[Even Rouault]

Chris,

> I'm just having some trouble understanding what cct is doing.  I'm
> attempting to do a helmert transformation corresponding to  EPSG coordinate
> operation 9082.  
> http://www.epsg-registry.org/report.htm?type=selection&entity=urn:ogc:def:c
> oordinateOperation:EPSG::9082&reportDetail=long&title=&reportDetail=long&tit
> le=&reportDetail=long&style=urn:uuid:report-style:default-with-urn&style_nam
> e=OGP%20Default%20With%20Urn&title=9082&r=63
> 
> The command I am running is
> 
> cct -vvv -t 2016.5 -d 9 +proj=helmert +ellps=GRS80
> +convention=coordinate_frame +t_epoch=2000.0 +x=0.00480 +y=0.00209
> +z=-0.01767 +rx=-0.00016508 +ry=0.000226897 +rz=0.00011984 +s=0.00140901
> +dx=0.00079 +dy=-0.00060 +dz=-0.00134 +drx=-0.00001347 +dry=0.00001514
> +drz=0.00001973 +ds=-0.00010201 testcct.in
> 
> The input file testcct.in just contains one coordinate, 173 -41 0.

+proj=helmert operates in the cartesian/geocentric coordinate space, so you can't directly 
provide / get geographic coordinates into/from it. You need to create a pipeline with a "+step 
+proj=cart +ellps=GRS80" before +proj=helmert and a "+step +inv +proj=cart +ellps=GRS80" 
after

Even

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