RPMs and *.desktop files

[Julius Schwartzenberg]

Hi,
I'm creating RPM packages and I want to include *.desktop files with 
them that are automaticly installed in the correct directory.
Because the directory can differ from one distro to another, I already 
figured I needed to do the creation of the files in the postinstall 
section of the RPM.
When detecting where to put the files, the default XDG_DATA_DIRS lists 
/usr/local/share as more important than /usr/share though. I'm putting 
the files of my program in /usr and not /usr/local, so /usr would also 
seem more appropriate for the *.desktop files.
How can I properly detect where the *.desktop files should go?
Thanks in advance,
Julius