Geodetic data (.gps) file format

by Peter Bird, 2002.08.04

A (.gps) geodesy file gives only horizontal-plane velocity components and error ellipses for each benchmark. Such files may be displayed in maps created by FiniteMap or NeoKineMap, and are also used by OrbScore2 in the step of comparing finite element model predictions to reality.

If the complete covariance matrix for horizontal velocity components is available, it is placed in a second associated (.gp2) file. However, this file is not currently used by OrbScore2 (although it can be used by NeoKinema).

The .gps format is very like the format of v_nnr.dat by Corne Kreemer but it adds header lines (and optional station names on the right).

Each .gps file will have 3 lines of headers:

File name and source(s)
Fortran FORMAT, in ( ), for reading the data lines that follow the headers
E_lon_deg N_lat_deg v_E_mmpa v_N_mmpa v_E_sigma v_N_sigma correlation frame identifier(s)

with the (obvious) meanings:

E_lon_deg = longitude, in degrees from Greenwich meridian, with East positive

N_lat_deg = latitude, in degrees from equator, with North positive

v_E_mmpa = velocity component to East, in millimeters per year

v_N_mmpa = velocity component to North, in millimeters per year

v_E_sigma = standard deviation (1-sigma) of v_E_mmpa, also in mm/a

v_N_sigma = standard deviation (1-sigma) of v_N_mmpa, also in mm/a

correlation = coefficient of correlation between v_E_mmpa and v_N_mmpa

reference_frame = reference frame for velocity, left-justified, limited to 15 bytes

identifier(s) = optional station name and/or source reference, if a compilation

 

Thus, the first few lines of v_nnr.dat, converted to .gps format, become:

v_nnr.gps, converted 2002.08.01 by Peter Bird from v_nnr.dat of Corne Kreemer (pers. comm. 2002 to Zhengkang Shen)
(    F9.3,    F10.3,    F9.3,    F9.3,    F10.3,    F10.3,      F12.3,1X,     A15,  1X,    A      )
E_lon_deg N_lat_deg v_E_mmpa v_N_mmpa v_E_sigma v_N_sigma correlation reference_frame identifier(s)
   77.110    43.900   30.125    0.532     1.000     1.000       0.000 NNR             [none]
   79.090    42.170   31.212    9.750     1.860     1.408      -0.054 NNR             [none]
   79.070    42.020   32.024    9.990     1.618     1.351      -0.041 NNR             [none]

Note that this standard allows the significant digits and column widths to be changed; just make corresponding changes in the Fortran FORMAT of line 2, and in the abbreviated headers of line 3. (However, unless there are radical improvements in accuracy, there does not seem to be any good reason to change.)