taskGNU Astronomy Utilities - Tasks: task #14368, No fits correction for modular...

 
 

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task #14368: No fits correction for modular warpings

Submitter:  Mohammad Akhlaghi <makhlaghi>
Submitted:  Fri 10 Feb 2017 01:28:57 AM UTC
   
 
Should Start On:  Thu 09 Feb 2017 03:00:00 PM UTC Should be Finished on:  Thu 09 Feb 2017 03:00:00 PM UTC
Category:  Warp Priority:  5 - Normal
Item Group:  Enhancement Status:  Done
Privacy:  Public Assigned to:  makhlaghi
Percent Complete:  100% Open/Closed:  Closed
Effort:  0.00

Mon 13 Feb 2017 11:13:15 PM UTC, comment #1: 

This has been applied and pushed to my development branch.

Mohammad Akhlaghi <makhlaghi>
Group administrator
Fri 10 Feb 2017 01:28:57 AM UTC, original submission:  

The FITS standard defines the center of the first pixel to have a coordinate value of 1.0 along every dimension. As a result, the center of coordinates is defined to be the half a pixel outside the input image.

As a result, when using the higher-level modular warpings (for example `--align', `--rotate', `--scale', `--translate', or `--project') ImageWarp will currently shift the center of coordinates by (+0.5, +0.5) so the bottom left corner of the first pixel will be at the coordinates of 0.0.

By by preferentially correcting one side of the image, this behavior can cause very confusing behavior (for example task #14363). Currently ImageWarp has the `--nofitscorrect' option to stop this correction on modular warpings.

So I am thinking that if we remove this higher-level correction so the edge pixels on both sides of the image will be similarly affected by the warping. This can help avoid confusions about how ImageWarp operates.

If users like to have preferential behavior on one side of the image (put the center of coordinates at the bottom left corner of the first pixel), they we can reverse the `--nofitscorrect' option, with an option like `--centeroncorner'. Alternatively, they can use the `--translate' (`-t') option before an after their desired transformation, like below:


$ astimgwarp -t0.5 --scale=2 -t-0.5 img.fits


As part of task #14245, I have just started working on ImageWarp, so I wanted to see what your comments on this are.

Mohammad Akhlaghi <makhlaghi>
Group administrator

 

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