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The input/output in light blue is in the sky plane. The input/output in green is the mask plane.
Iraf procedures are in CAPITAL letters.
The only use of actual distorsions is in LEN_SLITSLITS. This procedure is only run on the slit edges.
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# Open X-Projection mapping
fdx = open (XPROJ_MAP, READ_ONLY, TEXT_FILE)
call gs_ingest (fdx, asfx, asfy)
do i = 0, nslit-2 {
ndx1 = Memi[bufi+i]
ndx2 = Memi[bufi+i+1]
pc1 = PCODE(sdat,ndx1)
pc2 = PCODE(sdat,ndx2)
# If both are alignment boxes, just go on ...
if (pc1 == CODE_AS && pc2 == CODE_AS) # no problem
next
# We will need to recalculate something ...
xlow = X2(sdat,ndx1) + SLIT_GAP(indat)
xupp = X1(sdat,ndx2) - SLIT_GAP(indat)
xcen = 0.5 * (xlow + xupp)
yas = Y2(sdat,ndx1)
dxlow = gseval (asfx, xcen, yas)
yas = Y1(sdat,ndx2)
dxupp = gseval (asfx, xcen, yas)
dxavg = 0.5 * (dxupp + dxlow)
dxlow = dxlow - dxavg
dxupp = dxupp - dxavg
call eprintf ("%6.3f %6.3f\n")
call pargr (dxlow)
call pargr (dxupp)
if (pc1 == CODE_AS) {
del1 = 0.
del2 = X1(sdat,ndx2) - xlow - (dxupp - dxlow)
} else if (pc2 == CODE_AS) {
del1 = xupp - X2(sdat,ndx1) + (dxlow - dxupp)
del2 = 0.
} else {
del1 = xcen - 0.5*SLIT_GAP(indat) - X2(sdat,ndx1) + dxlow
del2 = X1(sdat,ndx2) - (xcen + 0.5*SLIT_GAP(indat)) - dxupp
}
X2(sdat,ndx1) = X2(sdat,ndx1) + del1
if (del1 != 0. && RELPA(sdat,ndx1) != INDEF) {
tana = tan (RELPA(sdat,ndx1))
Y2(sdat,ndx1) = Y2(sdat,ndx1) + del1 * FLIP * tana
}
X1(sdat,ndx2) = X1(sdat,ndx2) - del2
if (del2 != 0. && RELPA(sdat,ndx2) != INDEF) {
tana = tan (RELPA(sdat,ndx2))
Y1(sdat,ndx2) = Y1(sdat,ndx2) - del2 * FLIP * tana
}
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The other distorsion (based on an optical model of Keck) is done at PROJ_TO_MASK phase.