function az_ang,sN,cN,sp,cp,sa,ca,sb,cb,sg,cg,X,Y,rpr

; This function restores the Azimuth Angle phi' given an initial azimuth
; and nadir angle along with the offset Euler angles of a coordinate rotation:
; alpha, beta and gamma, the offset coordinates X, Y and Z between a
; pair of images and the altitude and radius of the planet being imaged
; Transformation derived with no restrictions on X, Y, and Z.  r is computed
; as a function of nadir angle for a spherical planet's surface by na_to_r
; v2 by B. Rizk 11/24/97
; v3 by B. Rizk 12/15/97 to implement the distortion versus the undistortion
;    transformations
; v4, v5 by B. Rizk 12/17/97 to speed up processing
; v6 by B. Rizk 3/11/98 to implement more useful coordinate transformation
;    (alpha, beta, gamma instead of gamma, beta, alpha rotation)

num=Y+rpr*(-sN*cp*cb*sg-sN*sp*sa*sb*sg+sN*sp*ca*cg-cN*ca*sb*sg-cN*sa*cg)
denom=X+rpr*(sN*cp*cb*cg+sN*sp*sa*sb*cg+sN*sp*ca*sg+cN*ca*sb*cg-cN*sa*sg)

az=atan(num,denom)

return,az*!radeg
end