Sotid is provided under GNU public license.
You can find the full text of the license on Web at 
http://www.gnu.org/copyleft/gpl.html

You can use, modify source code, distribute source code and/or software
which uses sotid provided 

a) you agree to keep original copyleft notice in source code with the date
   of creation and name of the author of the original.

b) in the case if you modify source code you agree to change the name of 
   the files and program units in order to distinguish them from the original
   version. You also agree to add the notice in each changed file stating
   the date and the nature of changes.


If you use either original or modified version of sotid for the work which 
result in scientific publication you agree to include the reference:

  Petrov, L., Study of harmonic site position variations determined by VLBI, 
submitted to J. Geophys. Res., 10.1029/2002JB001801, 2002.



