[PROJ] Plate motion models

[Even Rouault]

Hi Steve,

Assuming lon=-100 lat=40 z=0,  I believe (not sure! and in particular if 
that's geodetically meaningful to chain so many transformations) you 
should use a pipeline like the following one, which will do:

- conversion to cartesian coordinate space

- apply the ITRF2000 to ITRF2014 transformation preserving observation 
epoch of 2022.1

- apply the ITRF2014:NOAM model using a target epoch of 2010 (hence the 
+inv, as naturally the transformation would use +t_epoch as the 
"source") for a point at observation epoch of 2022.1

- force the observation epoch to 2010

- apply the ITRF2014 to ITRF2000 transformation (at epoch 2010)

- conversion to lat, lon coordinate space

echo -100 40 0 2022.1 | cct -d 8 +proj=pipeline \
     +step +proj=cart +ellps+GRS80 \
     +step +inv +init=ITRF2014:ITRF2000 \
     +step +inv +init=ITRF2014:NOAM +t_epoch=2010 \
     +step +proj=set +v_4=2010 \
     +step +init=ITRF2014:ITRF2000 \
     +step +inv +proj=cart +ellps+GRS80

I get:

-99.99999790     40.00000064    0.00755196     2010.0000

If using ITRF2008 instead of ITRF2014, I get:

   -99.99999854     40.00000065    0.00909276     2010.0000


I've also tried using a plate-fixed CRS as an intermediate using what is 
available in EPSG

First with NAD83(CORS96) since there's a direct transformation for it in 
EPSG (not quite "direct" since when looking at the comments, it already 
results from concatenation of ITRF96>97 and IERS ITRF97>2000 
transformations)

(order is lat, lon here)

$ echo 40 -100 0 2022.1 | cs2cs -d 8 "ITRF2000" "NAD83(CORS96)" | cct -d 
8 +proj=set +v_4=2010 | cs2cs -d 8 "NAD83(CORS96)" "ITRF2000"
40.00000067    -99.99999766 -0.00447640     2010.0000

Or if using NAD83(2011) (there's a transformation between NAD83(2011) 
and ITRF2008 in EPSG (concatenation of ITRF96>97 and IERS ITRF97>2008 
transformations), and PROJ will use the ITRF2008 to ITRF2000 
transformation in addition

$ echo 40 -100 0 2022.1 | cs2cs -d 8 "ITRF2000" "NAD83(2011)" | cct -d 8 
+proj=set +v_4=2010 | cs2cs -d 8 "NAD83(2011)"  "ITRF2000"
40.00000066    -99.99999765 -0.00447668     2010.0000


So results are somewhat consistent, at least in the lat, lon space (not 
for z values)

Best regards,

Even


Le 07/02/2022 à 14:49, Steve Riddell a écrit :
>
> The data for the ITFR2008 & ITRF2014 plate motion models are delivered 
> with PROJ as init files. From the documentation, 8.7, I think I see 
> how an +init proj string can be used for changing epochs between ITFR 
> frames (e.g. ITRF2000 to ITRF2005), but can someone please give an 
> example of using the plate models? For example, if I have a point in 
> ITRF2000 epoch 2022.1 and I want to use the NOAM plate model to move 
> it to 2010.0, what would be the +init string? I’m assuming cct would 
> be an appropriate application for processing this string?
>
> Thanks for any assistance!
>
> Steve
>
>
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> PROJ at lists.osgeo.org
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