Based on the UTC time of the image and the PRF and number of lines, basically the program getorb is called through a UNIX system call. Functions from the standard library ctime (or time.h) are used for the time conversions. This call is echoed to the screen as DEBUG. The commands can be executed stand-alone as well.
%getodr 950727094923,950727094945,1 /data/orbits/ERS2.ARCS > dummyout
%
%(...read in ODR file name from dummyout (ODR.422))
%untar /data/orbits/ERS1.ARCS ODR.422
getorb 950727094923,950727094945,1 /data/delftorbits/ERS1/ \
> scratchorbit
The ephemerides are first written to a dummy file (named "scratchorbit") and later placed in the result file (without the velocity output, only t,x,y,z). It has been noted that sometimes this scratch file is not automatically removed. This file can be savely removed by hand.
Natural cubic splines are used for the interpolation so it may be wise to have a short time-interval and some data before the first and after the last line.
If there is a section with the ephemerides of the SLC leaderfile in the master result file, then this section is removed.
In the routine splineinterpol, file utilities.c, where the coefficients are computed, __NATURALSPLINE__ is defined. This sets the boundary condition to use zero second derivative at the borders. Otherwise, the first derivative is set to a specified value. This does not seem to make a big difference.