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I'm using geomap and geotran to try to align two ccd direct images taken one right after another; the linear pixel shift is about half a pixel. I get a very nice geomap solution (rms < 0.1 pixel) but when I transform one of the images to match the other, there's a shift of nearly 5 pixels in the resultant image. I've tried varying just about every parameter but I'm total flumoxed by it.Here's what I did:
(a) Ran daofind on both ccd026.fits and ccd027.fits. I then used a fortran program to match coordinates and generate a file of ccd027x ccd027y ccd026x ccd026y. Call the file 236xyxy. I'll note that the median shifts are tiny, -0.269 and -0.129 pixels, in the sense of ccd027x-ccd026x and ccd027y-ccd026y. If I run imshift on ccd026 using these shifts, the images align well (but not perfectly, which is why I'm using geomap/trans
(b) I run geomap using 236xyxy. I use fitgeom=teneral, and order 3. I get great fits, with rms of <0.1 pixels. (There are many hundreds of points).
(c) I run geotran on ccd026. This should now transform the image so it's on the same system as ccd027, right? But instead if I now compare the coordinates of stars in the two images they differ by 0.15 pixels in x and 4.9 pixels in y. Trying to transform ccd027 instead and compare the result with ccd026 is no better; i.e., it's not like I've mixed up the reference and program images. I'm quite confused. The result appears to be independent of the kind of interpolation I'm using; linear, drizzle, spline3, etc.Here's my geomap parameters:
daophot> lpar geomap
input = "237xyxy" The input coordinate files
database = "geostuff" The output database file
xmin = INDEF Minimum x reference coordinate value
xmax = INDEF Maximum x reference coordinate value
ymin = INDEF Minimum y reference coordinate value
ymax = INDEF Maximum y reference coordinate value
(transforms = "") The output transform records names
(results = "") The optional results summary files
(fitgeometry = "general") Fitting geometry
(function = "polynomial") Surface type
(xxorder = 3) Order of x fit in x
(xyorder = 3) Order of x fit in y
(xxterms = "half") X fit cross terms type
(yxorder = 3) Order of y fit in x
(yyorder = 3) Order of y fit in y
(yxterms = "half") Y fit cross terms type
(maxiter = 11) Maximum number of rejection iterations
(reject = 3.) Rejection limit in sigma units
(calctype = "double") Computation type
(verbose = yes) Print messages about progress of task ?
(interactive = yes) Fit transformation interactively ?
(graphics = "stdgraph") Default graphics device
(cursor = "") Graphics cursor
(mode = "ql") Here are my geotran parameters:
input = ccd026 Input data
output = ccd026try9 Output data
database= geostuff Name of GEOMAP database file
transfor= 237xyxy Names of coordinate transforms in database file
(geometr= geometric) Transformation type (linear,geometric)
(xin = INDEF) X origin of input frame in pixels
(yin = INDEF) Y origin of input frame in pixels
(xshift = INDEF) X origin shift in pixels
(yshift = INDEF) Y origin shift in pixels
(xout = INDEF) X origin of output frame in reference units
(yout = INDEF) Y origin of output frame in reference units
(xmag = INDEF) X scale of input picture in pixels per reference uni
(ymag = INDEF) Y scale of input picture in pixels per reference uni
(xrotati= INDEF) X axis rotation in degrees
(yrotati= INDEF) Y axis rotation in degrees
(xmin = INDEF) Minimum reference x value of output picture
(xmax = INDEF) Maximum reference x value of output picture
(ymin = INDEF) Minimum reference y value of output picture
(ymax = INDEF) Maximum reference y value of output picture
(xscale = 1.) X scale of output picture in reference units per pix
(yscale = 1.) Y scale of output picture in reference units per pix
(ncols = INDEF) Number of columns in the output picture
(nlines = INDEF) Number of lines in the output picture
(xsample= 1.) Coordinate surface sampling interval in x
(ysample= 1.) Coordinate surface sampling interval in y
(interpo= spline3) Interpolant
(boundar= nearest) Boundary extension (nearest,constant,reflect,wrap)
(constan= 0.) Constant boundary extension
(fluxcon= yes) Preserve image flux?
(nxblock= 4096) X dimension of working block size in pixels
(nyblock= 4096) Y dimension of working block size in pixels
(verbose= yes) Print messages about the progress of the task
(mode = ql)Using the default nxblock=512 nyblock=512 doesn't change things.I've put the images and the file used for the mapping where you can get to them:
http://www.lowell.edu/users/massey/ccd026.fits
http://www.lowell.edu/users/massey/ccd027.fits
http://www.lowell.edu/users/massey/237xyxy
http://www.lowell.edu/users/massey/geostuffAny help would be greatly appreciated.---phil