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include <math.h>
define SZ_CDMTX 4
# PHYSTOPIX -- procedure to obtain pixel coordinates from the equatorial
# ones, giving the center position and scale of the frame.
procedure pixtoeq (plt_ra_cen, plt_dec_cen, plt_x_cen, plt_y_cen,
cdmtx, x, y, ra, dec)
double plt_ra_cen # Plate centre (radians)
double plt_dec_cen # " "
double plt_x_cen # Plate center in x (pixels)
double plt_y_cen # Plate center in y (pixels)
double cdmtx[SZ_CDMTX] # CD Matrix (cd11, cd12, cd21, cd22)
double ra # Objects RA position (radians)
double dec # Objects DEC position (radians)
double x # Position from centre (pixels)
double y # "
double xi # Standard coordinate (degrees)
double eta # "
double cd11, cd12, cd21, cd22
double xi_arcs, eta_arcs # Standard coord. in arc seconds.
begin
cd11 = cdmtx[1]
cd12 = cdmtx[2]
cd21 = cdmtx[3]
cd22 = cdmtx[4]
xi = cd11*(x-plt_x_cen) + cd12*(y-plt_y_cen)
eta = cd21*(x-plt_x_cen) + cd22*(y-plt_y_cen)
xi_arcs = xi*3600.0 # to arcs
eta_arcs = eta*3600.0
call trsteq (plt_ra_cen, plt_dec_cen, xi_arcs, eta_arcs, ra, dec)
end
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