taskGNU Astronomy Utilities - Tasks: task #15729, Warp on 3D cubes (at first 2D warp...


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task #15729: Warp on 3D cubes (at first 2D warp over third dimension)

Submitter:  Mohammad Akhlaghi <makhlaghi>
Submitted:  Thu 16 Jul 2020 08:05:59 PM UTC
Should Start On:  Wed 15 Jul 2020 11:00:00 PM UTC Should be Finished on:  Wed 15 Jul 2020 11:00:00 PM UTC
Category:  Warp Priority:  5 - Normal
Item Group:  Enhancement Status:  None
Privacy:  Public Percent Complete:  0%
Assigned to:  None Open/Closed:  Open
Effort:  0.00

Fri 17 Jul 2020 12:40:45 AM UTC, comment #1: 

As a demonstration of treating each slice as an independent 2D dataset, see crop-3d-as-2d-slices.mk.

In this Makefile we first pull out each slice as a 2D image, do the operation (Crop with options like '--polygon', that aren't yet supported in 3D), then put them back into a cube with Arithmetic. As a Makefile (putting hell scripts in blobs, or Make 'rules'), the job can be done on multiple threads and thus much faster and cleaner than a simple shell script.

Something like this can easily go into the source of Warp for the first step described below.

But until then, if you need any other special Warp operation, it can easily be added to this Makefile, so it supports both Crop and/or Warp. Alternatively, it can easily be modified/duplicated for Warp-only (For example rotating without cropping). So please get in touch if you need such a feature.

Mohammad Akhlaghi <makhlaghi>
Project Administrator
Thu 16 Jul 2020 08:05:59 PM UTC, original submission:  

Currently Warp only works on 2D images. But an increasingly large fraction of astronomical data are being produced as 3D cubes, so it would be very useful if Warp could also be used on them.

The main technical difficulty is that on a 2D surface, we have polygons that can represent the pixels in the warped grid. But in 3D we would need 3D polygons which are much more complex.

However, one advantage with most (almost all, as far as I know!) cubes is that their third dimension is independent of the first two by physical nature (the first two are usually spatial dimensions: RA and Dec) and the third is spectral. So very rarely will one want to do a warp that includes a mixing of the first two, and third dimension.

So as a first step in this task, Warp can treat the 3D cube as independent 2D images, do the warping on each, then stack them back into a 3D cube.

Mohammad Akhlaghi <makhlaghi>
Project Administrator


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