Only FOC images currently undergo geometric correction during standard pipeline processing (the. Observers should be aware that these tasks do not correct for geometric distortion. Table 3.1 lists some additional tasks that draw on the standard astrometry keywords. To find the RA and Dec of the current pixel, you supply these coordinates to xy2rd by typing (The task rd2xy inverts this operation.) SAOimage displays the current x,y pixel location of the cursor in the upper-left corner of the window. xy2rd: Translates x and y pixel coordinates to RA and Dec.Simply open an SAOimage window and type, for example: disconlab: Displays your image with a superimposed RA and Dec grid.Two simple tasks that draw on these keywords to relate your image to sky coordinates are: IRAF/STSDAS tasks can use this information to convert between pixel coordinates and RA and Dec. The header of every calibrated HST two-dimensional image contains a linear astrometric plate solution, written in terms of the standard FITS astrometry header keywords: CRPIX1, CRPIX2, CRVAL1, CRVAL2, and the CD matrix-CD1_1, CD1_2, CD2_1, and CD2_2. Methods for improving your absolute astrometric accuracy.Tasks that supply positional information about HST images.
#HST ASTROMETRY HOW TO#
This section describes how to determine the orientation of an HST image and the RA and Dec of any pixel or source within it, including: Working with STIS, ACS, and NICMOS imsets.Relating your image to sky coordinates.This section describes methods for using STSDAS and IRAF to work with two-dimensional image data from HST.
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