mainGNU Astronomy Utilities - Support: sr #109222, Reassigned to another tracker...


sr #109222: Reassigned to another tracker [was: ImageWarp 'rotate' does not correctly propagate WCS pixel scale information into header]

Submitter:  Lee Kelvin <leeskelvin>
Submitted:  Tue 17 Jan 2017 04:36:19 PM UTC
Category:  Warp Priority:  5 - Normal
Severity:  3 - Normal Item Group:  * Output not reasonable
Status:  None Privacy:  Public
Assigned to:  None Open/Closed:  Closed
Operating System:  GNU/Linux
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Wed 18 Jan 2017 01:20:44 AM UTC, comment #1: 


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Mohammad Akhlaghi <makhlaghi>
Group administrator
Tue 17 Jan 2017 04:36:19 PM UTC, original submission:  

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.

Lee Kelvin

Lee Kelvin <leeskelvin>


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    Follow 3 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2017-01-18 makhlaghi Reassign ItemGNU Astronomy Utilities, sr #109222 GNU Astronomy Utilities, bug #50073
    2017-01-17 leeskelvin Attached File- Added input.fits, #39494
        Attached File- Added input_warped.fits, #39495

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