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[gnuastro-devel] [sr #109222] ImageWarp 'rotate' does not correctly prop
From: |
Lee Kelvin |
Subject: |
[gnuastro-devel] [sr #109222] ImageWarp 'rotate' does not correctly propagate WCS pixel scale information into header |
Date: |
Tue, 17 Jan 2017 16:36:20 +0000 (UTC) |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36 |
URL:
<http://savannah.gnu.org/support/?109222>
Summary: ImageWarp 'rotate' does not correctly propagate WCS
pixel scale information into header
Project: GNU Astronomy Utilities
Submitted by: leeskelvin
Submitted on: Tue 17 Jan 2017 04:36:19 PM GMT
Category: ImageWarp
Priority: 5 - Normal
Severity: 3 - Normal
Item Group: Output not reasonable
Status: None
Privacy: Public
Assigned to: None
Originator Email:
Open/Closed: Open
Discussion Lock: Any
Operating System: GNU/Linux
_______________________________________________________
Details:
On applying an image rotation using ImageWarp, the World Coordinate System
(WCS) pixel scale information is only partially transferred to the output
image.
The attached image 'input.fits' is a 3x3 pixel image with WCS information in
the header defined using the CDi_j FITS standard formalism. The pixel scale
for this image is 0.339 arcsec/pixel, i.e., 9.4166667e-5 degrees/pixel.
A 360-degree image rotation is performed on this image using the command:
astimgwarp --rotate=360 input.fits
This produces the output image 'image_warped.fits', attached to this report.
The pixel flux values have been correctly preserved, and the output image is
aligned precisely with the input image, as expected for a 360-degree rotation.
WCS information in the rotated image header has been translated from the CDi_j
formalism to the PCi_j formalism. This requires not only PC1_1 and PC2_2 in
the header, but also CDELT1 and CDELT2 values. CDELTn values describe the
"physical increment at the reference pixel", giving the pixel scale in degrees
per pixel.
Whilst the pixel scale is correctly preserved in the output PCi_j header
values, both CDELTn values are equal to 1, incorrectly implying that each
pixel is 1 degree in size. This creates problems in, e.g., DS9 when viewing
the two files attached to this report side by side and matching by WCS. I
would expect the pixel scale to be correctly propagated through to the output
header CDELTn parameters.
Regards,
Lee Kelvin
_______________________________________________________
File Attachments:
-------------------------------------------------------
Date: Tue 17 Jan 2017 04:36:19 PM GMT Name: input.fits Size: 8kB By:
leeskelvin
<http://savannah.gnu.org/support/download.php?file_id=39494>
-------------------------------------------------------
Date: Tue 17 Jan 2017 04:36:19 PM GMT Name: input_warped.fits Size: 8kB
By: leeskelvin
<http://savannah.gnu.org/support/download.php?file_id=39495>
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