A have assembled OTW routines that perform gnomonic projection task. Initially I used single precision, but later I added double precision versions. I cover all versions here. Directly below I simply show examples of running the projection (rd2xy) and the inverse (xy2rd).

Usage: rd2xy_gnomSP.sh 161.956829167 12.581597222 162.069520833 12.62842222
arg1 - RAo in degrees
arg2 - DECo in degrees
arg3 - RA in degrees
arg4 - DEC in degrees

% rd2xy_gnomSP.sh 161.956829167 12.581597222 162.069520833 12.628422222
      -395.899        168.651        430.324      66.926
% rd2xy_gnomDP.sh 161.956829167 12.581597222 162.069520833 12.628422222
      -395.876        168.655        430.305      66.925

Usage: xy2rd_gnomSP.sh 161.956829167 12.581597222  -395.899  168.651 
arg1 - RAo in degrees
arg2 - DECo in degrees
arg3 - Xlin in arcseconds
arg4 - Ylin in arcseconds

% xy2rd_gnomSP.sh 161.956829167 12.581597222  -395.899  168.651 
10:48:16.6862 +12:37:42.315
% xy2rd_gnomDP.sh 161.956829167 12.581597222  -395.899  168.651 
10:48:16.6865 +12:37:42.316