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The other distorsion (based on an optical model of Keck) is done at PROJ_TO_MASK phase.GNOM_TO_DPROJ procedure.
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#
# GNOM_TO_DPROJ: adjust gnomonic coords to curved surface, take projection
# onto plane, and apply distortion correction, resulting in distortion-
# adjusted projected coords ready for a vertical projection to slitmask.
# Double inputs, outputs; outputs may be the same arguments as inputs.
#
#####
## NB: We assume Sutin's ray trace is already producing radii to curved surface.
####
procedure gnom_to_dproj (xg, yg, xd, yd)
double xg, yg # x,y gnomonic projection
double xd, yd # returned x,y projected on plane (distorted)
double rho # radius of input angle (approx from h)
double cosa, sina # cos, sin of azimuth in image plane
begin
rho= sqrt (xg * xg + yg * yg)
cosa = yg / rho
sina = xg / rho
# Apply map gnomonic projection --> real telescope
rho = rho * (1. + DIST_C0 + DIST_C2 * rho * rho)
xd = rho * sina
yd = rho * cosa
end
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In this procedure, DIST_C0 = 0.0e-4 and DIST_C2 = -1.111311e-8