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define MAX_ITERATIONS 20
# CCGSXY -- Routine for computing X,Y pixel position from a given RA and Dec
# on a GSSS plate.
procedure ccgsxy (plate_centre_ra,
plate_centre_dec,
plate_centre_x,
plate_centre_y,
x_pixel_size,
y_pixel_size,
plate_scale,
amd_x,
amd_y,
object_x,
object_y,
object_mag,
object_col,
object_ra,
object_dec)
double plate_centre_ra #Plate Right Ascension (radians)
double plate_centre_dec #Plate Declination (radians)
double plate_centre_x #Position used in soln.(microns)
double plate_centre_y # "
double x_pixel_size #Scan pixel size (microns)
double y_pixel_size # "
double plate_scale #Plate scale (arcsec/mm)
double amd_x[20] #Plate model coefficients
double amd_y[20] # "
double object_x #Pixel position for object
double object_y # "
double object_mag #Object magnitude
double object_col #Colour
double object_ra #Object RA (radians)
double object_dec # " Dec
double xi_object #Standard coords (arcsec)
double eta_object # "
double x #Position from centre (mm)
double y # "
double delta_x #correction to x
double delta_y #correction to y
int n_iterations #no.iterations used
double f #Function for x model
double g #Function for y model
double fx #Deriv. x model wrt x
double gx #Deriv. y model wrt x
double fy #Deriv. x model wrt y
double gy #deriv. y model wrt y
int ierr #Stats flag
begin
#
# Convert RA and Dec to standard coordinates
#
call treqst (plate_centre_ra, plate_centre_dec,
object_ra, object_dec, xi_object, eta_object)
# Iterate by Newtons method
n_iterations = 0
ierr = 0
# Get initial estimate of x,y
x = xi_object / plate_scale
y = eta_object / plate_scale
while (ierr == 0) {
n_iterations=n_iterations+1
#
# X plate model
#
f = amd_x(1)*x +
amd_x(2)*y +
amd_x(3) +
amd_x(4)*x*x +
amd_x(5)*x*y +
amd_x(6)*y*y +
amd_x(7)*(x*x+y*y) +
amd_x(8)*x*x*x +
amd_x(9)*x*x*y +
amd_x(10)*x*y*y +
amd_x(11)*y*y*y +
amd_x(12)*x*(x*x+y*y) +
amd_x(13)*x*(x*x+y*y)**2 +
amd_x(14)*object_mag +
amd_x(15)*object_mag**2 +
amd_x(16)*object_mag**3 +
amd_x(17)*object_mag*x +
amd_x(18)*object_mag*(x*x+y*y) +
amd_x(19)*object_mag*x*(x*x+y*y) +
amd_x(20)*object_col -
xi_object
#
# Derivative of X model wrt x
#
fx = amd_x(1) +
amd_x(4)*2.0*x +
amd_x(5)*y +
amd_x(7)*2.0*x +
amd_x(8)*3.0*x*x +
amd_x(9)*2.0*x*y +
amd_x(10)*y*y +
amd_x(12)*(3.0*x*x+y*y) +
amd_x(13)*(5.0*x**4+6.0*x*x*y*y+y**4) +
amd_x(17)*object_mag +
amd_x(18)*object_mag*2.0*x +
amd_x(19)*object_mag*(3.0*x*x+y*y)
#
# Derivative of X model wrt y
#
fy = amd_x(2) +
amd_x(5)*x +
amd_x(6)*2.0*y +
amd_x(7)*2.0*y +
amd_x(9)*x*x +
amd_x(10)*x*2.0*y +
amd_x(11)*3.0*y*y +
amd_x(12)*2.0*x*y +
amd_x(13)*4.0*x*y*(x*x+y*y) +
amd_x(18)*object_mag*2.0*y +
amd_x(19)*object_mag*2.0*x*y
#
# Y plate model
#
g = amd_y(1)*y +
amd_y(2)*x +
amd_y(3) +
amd_y(4)*y*y +
amd_y(5)*y*x +
amd_y(6)*x*x +
amd_y(7)*(x*x+y*y) +
amd_y(8)*y*y*y +
amd_y(9)*y*y*x +
amd_y(10)*y*x*x +
amd_y(11)*x*x*x +
amd_y(12)*y*(x*x+y*y) +
amd_y(13)*y*(x*x+y*y)**2 +
amd_y(14)*object_mag +
amd_y(15)*object_mag**2 +
amd_y(16)*object_mag**3 +
amd_y(17)*object_mag*y +
amd_y(18)*object_mag*(x*x+y*y) +
amd_y(19)*object_mag*y*(x*x+y*y) +
amd_y(20)*object_col -
eta_object
#
# Derivative of Y model wrt x
#
gx = amd_y(2) +
amd_y(5)*y +
amd_y(6)*2.0*x +
amd_y(7)*2.0*x +
amd_y(9)*y*y +
amd_y(10)*y*2.0*x +
amd_y(11)*3.0*x*x +
amd_y(12)*2.0*x*y +
amd_y(13)*4.0*x*y*(x*x+y*y) +
amd_y(18)*object_mag*2.0*x +
amd_y(19)*object_mag*y*2.0*x
#
# Derivative of Y model wrt y
#
gy = amd_y(1) +
amd_y(4)*2.0*y +
amd_y(5)*x +
amd_y(7)*2.0*y +
amd_y(8)*3.0*y*y +
amd_y(9)*2.0*y*x +
amd_y(10)*x*x +
amd_y(12)*3.0*y*y +
amd_y(13)*(5.0*y**4+6.0*x*x*y*y+x**4) +
amd_y(17)*object_mag +
amd_y(18)*object_mag*2.0*y +
amd_y(19)*object_mag*(x*x+3.0*y*y)
delta_x = (-f * gy + g * fy) / (fx * gy - fy * gx)
delta_y = (-g * fx + f * gx) / (fx * gy - fy * gx)
x = x + delta_x
y = y + delta_y
if (dmax1 (dabs(delta_x), dabs(delta_y),
dabs(f), dabs(g)) < 1.e-5)
ierr=1
if (n_iterations == MAX_ITERATIONS)
ierr=2
}
# Convert x,y from mm about plate centre to pixels
object_x = (plate_centre_x - x*1000.0d0) / x_pixel_size
object_y = (plate_centre_y + y*1000.0d0) / y_pixel_size
end
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