xdshifts: Compute shifts using image display and centroiding techniques

Package: xdimsum

Usage

xdshifts inlist refim shiftlist cradius

Parameters

inlist

The list of input images for which offsets are to be computed.

refim

The reference image which defines the origin of the offsets. The reference images must be one of the images in the input image list. If refim is undefined the first input image is the reference image.

shiftlist

The output offsets file suitable for input to the xnregistar task. The output file contains the input image name, the x offset in pixels, the y offset in pixels, and the default exposure time which is always 1 in columns 1 through 4.

cradius

The centroiding radius in pixels.

datamin = INDEF, datamax = INDEF

The lower and upper bad data limits used by the centroiding algorithm.

background = INDEF

The mean background level for the centroiding algorithm.

niterate = 3

The maximum number of iterations performed by the centroiding algorithm.

maxshifts = 5

The maximum difference in pixels between the final computed offset and the offset predicted by displaying the images and marking reference stars in each image.

chkshifts = no

Edit the lists of input image reference stars, the list of registration stars, and the final offsets interactively?

Description

XDSHIFTS computes the offsets required to mosaic the images in the input image list inlist to the reference image refim using the image display and the IMEXAMINE and IMCENTROID tasks and writes the results to the output file shiftlist.

XDSHIFTS calls IMEXAMINE 3 times to perform the following functions:

o display the images so that the user can select a reference star
  common to all the images

o display the images so that the user can mark the position of the
  reference star in each image and create a reference star list

o display the reference image so that the user can mark the positions
  of several registration stars that will be used to a registration star
  list

The IMEXAMINE 'p' and 'n' keystroke commands or the ":select <image>" commands are used to select which image to display. The IMEXAMINE 'a' or 'r' keystroke command are used to mark and centroid the stars using pixels within cradius of the current best position. The 'q' keystroke terminates the current invocation of IMEXAMINE. More details on how IMEXAMINE computes the centroids and how to use the many features of IMEXAMINE can be found in the IMEXAMINE help page. If chkshifts is yes the user is given the opportunity to edit the reference star list and the registration star list.

Given the input image list, the reference image, the reference star list, the registration star list, and the centroiding parameters cradius, datamin, datamax, background, niterate, and maxshifts, XDSHIFTS calls the IMCENTROID task to recenter the registration objects and compute the offsets of each input image relative to the reference image refim. Detailed descriptions of the IMCENTROID task algorithms can be found in the IMCENTROID help page. If chkshifts is yes then the user is given the opportunity to edit the offsets file before it is finally output.

Examples

1. Compute the offsets file for the 25 sky subtracted demo images. Go ahead and register the images with xnregistar. The output image will appear in demo.mosaic and the output exposure map will appear in exp_demo.mosaic.

cl> type simlist
demo01.sub.imh
demo02.sub.imh
demo03.sub.imh
demo24.sub.imh
demo25.sub.imh

cl> xdshifts @simlist "" offsets 5.0





cl> xnregistar offsets demo.pl "" "" mosaic mosaic.exp mosaic.corners

Time requirements

Bugs

See also

imexamine,imcentroid