[PROJ] Transforming between ITRF realizations

[Alan Snow]

Hi Trey,

I tried it with pyproj and I got one answer:
>>> from pyproj import Transformer
>>> trans = Transformer.from_pipeline("+init=ITRF2000:ITRF93")
>>> trans.transform(-117.61748, 59.4967, 329.396)
(-111.83893294174032, 59.90053033616967, 330.56817290107665)

Then I used the `cct` tool and it seems to be slightly different:
$ cct --version
cct: Rel. 6.1.0, September 1st, 2019
$ cct +init=ITRF2000:ITRF93
-117.61748, 59.4967, 329.396
    -117.6048        59.5032      329.3751           inf

Do you have a result you are expecting?
Alan

On Fri, May 3, 2019 at 12:33 PM Trey Stafford <trey.stafford at nsidc.org>
wrote:

> Hello,
>
> I have a number of elevation datasets that each use a different ITRF
> realization. The coordinates in these datasets are referenced to the
> WGS84 ellipsoid. An example lon, lat, elev(meters above ellipsoid) tuple
> would be:
>
> -117.61748591770593, 59.496749040316935, 329.39612
>
> According to the proj4 documentation on Helmert transformations
> (https://proj4.org/operations/transformations/helmert.html), I should be
> able to use something like this to convert between ITRF2000 and ITRF93:
>
> proj +proj=helmert +convention=position_vector +x=0.0127 +y=0.0065
> +z=-0.0209 +s=0.00195 +dx=-0.0029 +dy=-0.0002 +dz=-0.0006 +ds=0.00001
> +rx=-0.00039 +ry=0.00080 +rz=-0.00114 +drx=-0.00011 +dry=-0.00019
> +drz=0.00007 +t_epoch=1988.0
>
> However, entering my coordinates yield the following result:
>
> 0.05    -0.01 329.39612
>
> I've used proj4 previously, but not to do transformations between
> different ITRF realizations. I suspect I am missing something, but I
> have not had revelations yet. Any suggestions or insight would be
> greatly appreciated!
>
> Thanks,
>
> Trey Stafford
>
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-- 
Alan Snow
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