[gnuastro-devel] [bug #55740] Diamond like shapes in nearst-ngb interpolation affecting NoiseChisel

[Mohammad Akhlaghi]

URL:
  <https://savannah.gnu.org/bugs/?55740>

                 Summary: Diamond like shapes in nearst-ngb interpolation
affecting NoiseChisel
                 Project: GNU Astronomy Utilities
            Submitted by: makhlaghi
            Submitted on: Tue 19 Feb 2019 08:38:41 PM UTC
                Category: NoiseChisel
                Severity: 4 - Important
              Item Group: Output not reasonable
                  Status: In Progress
                 Privacy: Public
             Assigned to: makhlaghi
             Open/Closed: Open
         Discussion Lock: Any

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Details:

In the `gal_interpolate_close_neighbors', we weren't re-initializing the flags
of the interpolated neighbors prior to interpolation. As a result, after
finding the median operator for the first time on each thread, no other value
was sorted any more (the median finding function would assume its sorted).

This directly affected NoiseChisel in a very bad way: On the tiles where
outlier values fell right in the middle of the list of good neighbor values,
the outlier would be reported as the median (because the median is the middle
value!).

In practice, this caused diamond like structures around outlier tiles during
NoiseChisel's threshold finding and Sky estimation steps.

This bug came up during a discussion with Roberto Baena Gallé.




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