Specifications of Station Position Evolution 
Format version 2025.07.20

In general, dependence of station position with time can be
represented as function of time in a form

X(t) = X0  + 
       X'(t - t0)  +  
       sum j=i,i=N ( Hc_i cos omega_i t + Hs_i sin omega_i t )  +  
       sum k=1-m, k=n-1 f_k Bm_k (t_k)

where the first term describes position at the reference epoch t0
the second term describes linear rate of change, the third term 
accounts for harmonic position variations, and the fourth term
accounts for non-harmonic motion described with a spline of
degree m, possibly with multiple knots. In addition, other 
functional dependence of non-linear motion is possible.

The station position evolution file describes the dependence of 
station position on time in a form of time series with a fixed 
time span.

======================================================================================
Byte-by-byte Description:
--------------------------------------------------------------------------------------
Bytes Format Units Label   Explanations
--------------------------------------------------------------------------------------

 1- 8 A8     ---   Name    IVS station name
10-28 A19    ---   CalDate Calendar date of the epoch in YYYY.MM.DD-hh:mm:ss format
30-34 I5     days  MJDDate MJD of the epoch
36-42 F7.1   sec   TAIDate TAI of the epoch after the midnight
44-56 F13.4  meter Xpos    X-coordinate of station position on a given epoch
58-70 F13.4  meter Ypos    Y-coordinate of station position on a given epoch
72-84 F13.4  meter Zpos    Z-coordinate of station position on a given epoch
--------------------------------------------------------------------------------------