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I would like to transform a coordinate value from ITRF2014 (epoch 2018.18) to ITRF2014 (epoch 2010.00)

The ITRF2014 (epoch 2018.18) coordinate is: 5023564.4726, 1677795.7877, -3542025.8348
The GNSS velocities in the SCC file found here for the station reads:

30305M001 GNSS CTWN  5023564.3613  1677795.6032 -3542025.9099 0.0006 0.0005 0.0007  1 00:000:00000 10:343:00000  
30305M001   0.00398       0.01912       0.01639 .00015 .00008 .00011  
30305M001 GNSS CTWN  5023564.3743  1677795.6082 -3542025.9213 0.0007 0.0006 0.0008  2 10:343:00000 11:330:00000  
30305M001  0.00398       0.01912       0.01639 .00015 .00008 .00011  
30305M001 GNSS CTWN  5023564.4298  1677795.6287 -3542025.9579 0.0007 0.0006 0.0008  3 11:330:00000 00:000:00000  
30305M001  0.00398       0.01913       0.01639 .00015 .00008 .00011

How do I go from 5023564.4726, 1677795.7877, -3542025.8348 ITRF2014 (epoch 2018.18) to
-> ITRF2014 (2010.0)?
Can you please show me how to get a ITRF2014 (2010.0) coordinate value?

Update (Gabriel De Luca suggestion)

first 10-years (343days): 0.0006 0.0005 0.0007
last 11-years (somedays): 0.0007 0.0006 0.0008

*(8.18)
0.004980 0.00409 0.005726
0.005726 0.00491 0.006544

itrf2014 (2018.8) 5023564.4726, 1677795.7877, -3542025.8348

itrf2014 (2010.0) with first 10: 5023564.4677 1677795.7836 -3542025.8405
itrf2014 (2010.0) with last 11: 5023564.4669 1677795.7828 -3542025.8413

Which one? Why are none of these the xyz values in the SCC file?

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6
  • I love seeing these kind of questions. I would be tempted to subtract 8.18 times the speed defined in the first line (that of the first 10 years and 343 days) from each coordinate. There appears to be no post-seismic deformation near Cape Town.
    – Gabriel De Luca
    Commented Oct 21, 2022 at 2:33
  • @GabrielDeLuca ---please see edit.
    – arkriger
    Commented Oct 21, 2022 at 11:53
  • I can't help. You want to transform only 8.18 years. I was thinking in subtract 8.18 (years) x 0.00398 (meters/year) for the X, for example. Also, don't understand why you are expecting to return to the coordinates of the file. The coordinates at 2010.0 are defined, all other values are predictions. That's my understanding, but this is not something I do.
    – Gabriel De Luca
    Commented Oct 21, 2022 at 12:25
  • I am grateful for your response @GabrielDeLuca. Thank you. I might not understand correctly myself. The ITRF2014 (2018.18) are the actual station coordinates now. I thought that if I subtract the velocities*8.18 I would get the itrf2014 (2010.0) coordinates. But you are saying the (2010.00) coordinates are already there. Should I use the coordinate in the SCC file?
    – arkriger
    Commented Oct 21, 2022 at 16:21
  • Well, the file starts with: "ITRF2014 STATION POSITIONS AT EPOCH 2010.0 AND VELOCITIES. GNSS STATIONS", so I think the position of Cape Town I station at epoch 2010.0 must be there.
    – Gabriel De Luca
    Commented Oct 21, 2022 at 23:16

1 Answer 1

Reset to default
1

I would be tempted to subtract 8.18 times the velocities corresponding to the CTWN station (Cape Town I) for the first ten years and 343 days (there appears to be no post-seismic deformation near Cape Town):

import numpy as np
np.set_printoptions(formatter={'float':"{0:0.4f}".format})

ctwn_2018= np.array([5023564.4726, 1677795.7877, -3542025.8348])
velocities = np.array([0.00398, 0.01912, 0.01639])
velocities_sigmas = np.array([.00015, .00008, .00011])

deltas = -8.18 * velocities
ctwn_2010 = ctwn_2018 + deltas
print(ctwn_2010)

delta_sigmas = 8.18 * velocities_sigmas
print(delta_sigmas)

But it returns:
[5023564.4400 1677795.6313 -3542025.9689]
[0.0012 0.0007 0.0009]
Which are a few centimeters away from the expected coordinates.

If you want to know the CTWN station coordinates referenced to ITRF2014 propagated to 2010.0 (not propagated because it's the reference epoch) you can query it at the ITRF network page: https://itrf.ign.fr/en/network/list

1

Mark up the station, add it to selection:

2

And query its instantaneous position:

3

Wich returns:

The table below contains the ITRF2014 coordinates of the selected stations propagated at epoch 2010/01/01.
Contact : [email protected]

   DOMES    ID  PT |         X [m]                 Y [m]                 Z [m]         | sigma_X [m] sigma_Y [m] sigma_Z [m] |
-------------------|-------------------------------------------------------------------|-------------------------------------|
 30305M001 CTWN  A |  5.02356436127709e+06  1.67779560320604e+06 -3.54202590989722e+06 | 6.22583e-04 5.37125e-04 7.42351e-04 |
-------------------|-------------------------------------------------------------------|-------------------------------------|
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1
  • Looks like the first line is the correct one. You have been extremely helpful. Thank you.
    – arkriger
    Commented Oct 22, 2022 at 19:23

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