; DSKEW ;--------------------------------------------------------------- ;! Geometric interpolation correction for skew ;# Task IMAGE-UTIL OOP ;----------------------------------------------------------------------- ;; Copyright (C) 2013-2014 ;; Associated Universities, Inc. Washington DC, USA. ;; ;; This program is free software; you can redistribute it and/or ;; modify it under the terms of the GNU General Public License as ;; published by the Free Software Foundation; either version 2 of ;; the License, or (at your option) any later version. ;; ;; This program is distributed in the hope that it will be useful, ;; but WITHOUT ANY WARRANTY; without even the implied warranty of ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ;; GNU General Public License for more details. ;; ;; You should have received a copy of the GNU General Public ;; License along with this program; if not, write to the Free ;; Software Foundation, Inc., 675 Massachusetts Ave, Cambridge, ;; MA 02139, USA. ;; ;; Correspondence concerning AIPS should be addressed as follows: ;; Internet email: aipsmail@nrao.edu. ;; Postal address: AIPS Project Office ;; National Radio Astronomy Observatory ;; 520 Edgemont Road ;; Charlottesville, VA 22903-2475 USA ;----------------------------------------------------------------------- DSKEW LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC DSKEW: Interpolate an image to correct for input skew/rotation Input image INNAME Image name (name) INCLASS Image name (class) INSEQ 0.0 9999.0 Image name (seq. #) INDISK 0.0 9.0 Image disk drive # Output image OUTNAME Image name (name) OUTCLASS Image name (class) OUTSEQ -1.0 9999.0 Image name (seq. #) OUTDISK 0.0 9.0 Image disk drive # BLC 0.0 4096.0 Bottom left corner of image 0=>entire image TRC 0.0 4096.0 Top right corner of image 0=>entire image IMSIZE 0.0 Output image size pixels REWEIGHT 0.0 4.0 (1) Interpolation halfwidth (2) Minimum fraction of good pixels required (0->1/3) ---------------------------------------------------------------- DSKEW Type: Task Use: DSKEW does an interpolation of one image to correct for any skew or rotation. FITS image files from other institutions, particularly optical telescopes have coordinates described by PCi_j or CDi_j keywords in the FITS header. IMLOD and FITLD attempt to interpret these and are succesful when the coordinates are simple. However, frequently some degrees of skew is found by the optical software when fitting the image coordinates. Since AIPS does not support skew in its image coordinates, DSKEW is intended to read the PCi_j or CDi_j keywords back out of the image history file and write an image interpolated onto a coordinate grid very similar to the input grid but without the skew. Interpolation is done only in the first 2 dimensions. Unlike HGEOM, DSKEW will interpolate over blanked pixels so that it can fill in small blanked regions and handle edges without having to discard image area. NOTE: the input subimage is read into dynamically allocated memory. Very large input arrays may cause swapping on your computer. Adverbs: INNAME......The input image name. Standard defaults. INCLASS.....The input image class. Standard defaults. INSEQ.......The input image sequence number. 0 => high INDISK......The input image disk drive no. 0 => any OUTNAME.....The output image name. blank => Standard defaults based on INNAME. OUTCLASS....The output image class. Standard behavior. OUTSEQ......The output image seq. no., 0=> highest unique If >0; image will be created if new, overwritten if image name exists. OUTDISK.....Output disk drive no., 0=> highest with space BLC.........The bottom left-hand pixel of the input image which becomes the bottom left corner of the input subimage. The value (0,0) means (1,1). TRC.........The top right-hand pixel of the input image which becomes the top right corner of the subimage. The value (0,0) means take the top right hand corner of the image. IMSIZE......Output image size. 0 -> input image size after BLC and TRC are applied REWEIGHT....Interpolation kernel parameters: (1) Half width of the interpolating kernel (1 - 4). Default = 1 Larger support sizes should produce more accurate results at the cost of increased computation. However, if the image contains very small features, larger values may produce curious "overshoots" so that the output image has a rather larger maximum and rather more negative minimum than the input. (2) Minimum fraction of pixels in interpolation kernal area required for non-blanked output. <= 0 or >= 1 => 0.333 ----------------------------------------------------------------