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  1. Data Management
  2. DM-31417

Add makeHpxWcs to afwGeom to make an HPX SkyWcs object.

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    • Type: Story
    • Status: Done
    • Resolution: Done
    • Fix Version/s: None
    • Component/s: afw
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      Description

      As part of DM-31221, we need to be able to generate HIPS compatible HPX SkyWcs objects to warp coadds into the HPX projection used for HIPS viewing.

      In the investigation I found no documentation for how to do this in https://www.ivoa.net/documents/HiPS/20170519/REC-HIPS-1.0-20170519.pdf or in https://www.atnf.csiro.au/people/mcalabre/WCS/hpx.pdf (which describes a full-sky mapping rather than the single-pixel mapping used by HIPS). However, this is done in the Aladin java source code available here: http://aladin.u-strasbg.fr/java/AladinSrc.jar (linked from http://aladin.u-strasbg.fr/java/nph-aladin.pl?frame=downloading).

      This ticket ports the specific z-order mapping and related code used by the HPX code into afw.geom.makeHpxWcs to generate a SkyWcs suitable for use with the warping code.

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          erykoff Eli Rykoff added a comment -

          PR is here: https://github.com/lsst/afw/pull/603

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          erykoff Eli Rykoff added a comment - PR is here: https://github.com/lsst/afw/pull/603
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          womullan Wil O'Mullane added a comment - - edited

          I believe there are few cleanups  and name differentiations (is it HEALPix or HPX)  needed - then this is good to go. Plus the better description of tilepix as the number of projected pixels on the side of the HEALPIx pixel in the higher resolution projected space (or is it the inverse ..)

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          womullan Wil O'Mullane added a comment - - edited I believe there are few cleanups  and name differentiations (is it HEALPix or HPX)  needed - then this is good to go. Plus the better description of tilepix as the number of projected pixels on the side of the HEALPIx pixel in the higher resolution projected space (or is it the inverse ..)
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          erykoff Eli Rykoff added a comment -

          Wil O'Mullane Can you please take a look at the latest version? I've added more commentary and references, clarified the API (I hope!) and removed a couple of extraneous unused variables. I've tried to be clear about distinguishing between HEALPix the pixelization code and the HEALPix grid projection (HPX). Please let me know if there's anything missing.

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          erykoff Eli Rykoff added a comment - Wil O'Mullane Can you please take a look at the latest version? I've added more commentary and references, clarified the API (I hope!) and removed a couple of extraneous unused variables. I've tried to be clear about distinguishing between HEALPix the pixelization code and the HEALPix grid projection (HPX). Please let me know if there's anything missing.
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          womullan Wil O'Mullane added a comment -

          new comments and variable names make this much clearer !

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          womullan Wil O'Mullane added a comment - new comments and variable names make this much clearer !

            People

            Assignee:
            erykoff Eli Rykoff
            Reporter:
            erykoff Eli Rykoff
            Reviewers:
            Wil O'Mullane
            Watchers:
            Eli Rykoff, Wil O'Mullane
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            2 Start watching this issue

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