Alain,
you actually want to do 2 things:
- change the reference frame (from ITRF92 to ITRF2014)
- and change of coordinate epoch in one of the coordinate frames
(presumably in ITRF2014)
You can't do that just by using the 15-parameter ITRF92->ITRF2014
transformation.
So first step, change from ITRF92 to ITRF2014 at epoch 1993.0. You must
use +t_epoch=2010 as it is the canoncial central epoch of the transformation
$ echo -139.57736536 -8.95162075 2.234 1993.0 | cct -d 8
+proj=pipeline +step +proj=cart +ellps=GRS80 +step +proj=helmert
+x=-0.0154 +y=-0.0015 +z=0.0708 +rx=0 +ry=0 +rz=-0.00026 +s=-0.00309
+dx=-0.0001 +dy=0.0005 +dz=0.0033 +drx=0 +dry=0 +drz=-2e-05 +ds=-0.00012
+t_epoch=2010 +convention=position_vector +step +inv +proj=cart +ellps=GRS80
-139.57736535 -8.95162059 2.24172393 1993.0000
You can also that by using EPSG objects (but using lat, long order)
$ echo -8.95162075 -139.57736536 2.234 1993.0 | cs2cs -d 8 ITRF92 ITRF2014
-8.95162059 -139.57736535 2.24172393 1993.0
and second step, apply the Pacific plate motion Helmert transformation
for ITRF2014:
$ echo -139.57736535 -8.95162059 2.24172393 2023 | cct -d 8 \
+proj=pipeline +step +proj=cart +ellps=GRS80 \
+step +init=ITRF2014:PCFC +t_epoch=1993 \
+step +inv +proj=cart +ellps=GRS80
-139.57738390 -8.95161168 2.24071029 2023.0000
The ITRF2014:PCFC parameters are at
https://github.com/OSGeo/PROJ/blob/4762020db550ac3b9405970f8830abdb5fefdb48/data/ITRF2014#L51
If inlined:
$ echo -139.57736535 -8.95162059 2.24172393 2023 | cct -d 8
+proj=pipeline +step +proj=cart +ellps=GRS80 +step +proj=helmert
+drx=-0.000409 +dry=0.001047 +drz=-0.002169 +convention=position_vector
+t_epoch=1993 +step +inv +proj=cart +ellps=GRS80
-139.57738390 -8.95161168 2.24071029 2023.0000
The difference between the initial and final coordinate in ITRF2014 is
2.272 m.
$ echo -8.95162075 -139.57736536 -8.95161168 -139.57738390 | geod -I
+ellps=GRS80
-63d48'8.651" 116d11'51.359" 2.272
You could actually concatenate the 2 pipelines by using the +proj=set
+v_4=2023 operator to force the target epoch of the plate motion
transformation
$ echo -139.57736536 -8.95162075 2.234 1993.0 | cct -d 8
+proj=pipeline \
+step +proj=cart +ellps=GRS80 \
+step +proj=helmert +x=-0.0154 +y=-0.0015 +z=0.0708 +rx=0 +ry=0
+rz=-0.00026 +s=-0.00309 \
+dx=-0.0001 +dy=0.0005 +dz=0.0033 +drx=0 +dry=0
+drz=-2e-05 +ds=-0.00012 +t_epoch=2010 +convention=position_vector \
+step +proj=set +v_4=2023 \
+step +proj=helmert +drx=-0.000409 +dry=0.001047 +drz=-0.002169
+convention=position_vector +t_epoch=1993 \
+step +inv +proj=cart +ellps=GRS80
-139.57738390 -8.95161168 2.24071029 2023.0000
Even
Le 15/11/2022 à 17:16, Alain Orsoni a écrit :
Hello,
I’m trying to convert ITRF92 (epoch 93.0) coordinates to ITRF2014
epoch 2023.0.
Having some 8 cms per year movement I expect some 2.4m difference in
the coordinates.
I tried some syntaxes but did not understand clearly how (where) to
indicate the epochs (initial and final) in my tests :
One test applied was :
echo -139.57736536 -8.95162075 2.234 2023.0 | cct +proj=pipeline
+step +proj=cart +ellps=GRS80 +step +proj=helmert +x=-0.0154
+y=-0.0015 +z=0.0708 +rx=0 +ry=0 +rz=-0.00026 +s=-0.00309 +dx=-0.0001
+dy=0.0005 +dz=0.0033 +drx=0 +dry=0 +drz=-2e-05 +ds=-0.00012
+t_epoch=1993 +convention=position_vector +step +inv +proj=cart
+ellps=GRS80
Which gave me
-139.5773658008 -8.9516192265 2.1701 2023.0000
As result. Difference much lower than expected representing some 20 cm
variation from one epoch to the other.
I indicated the final epoch desired in my input and the initial epoch
in the helmert transform.
This is probably false, but I did not encounter this kind of
indication in the documentation.
Where is the misunderstanding?
Thank you for any help,
Alain Orsoni
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