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From "Martin Desruisseaux (JIRA)" <j...@apache.org>
Subject [jira] [Created] (SIS-446) NetCDF store should be robust to non-linear localization grid
Date Thu, 07 Mar 2019 11:40:00 GMT
Martin Desruisseaux created SIS-446:
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             Summary: NetCDF store should be robust to non-linear localization grid
                 Key: SIS-446
                 URL: https://issues.apache.org/jira/browse/SIS-446
             Project: Spatial Information Systems
          Issue Type: Task
          Components: Referencing, Storage
            Reporter: Martin Desruisseaux
            Assignee: Martin Desruisseaux
             Fix For: 1.0


Localization grid in netCDF files contain (longitude, latitude) values of all pixels. {{LocalizationGridBuilder}}
first computes a linear (affine) approximation of a localization grid, then stores only the
residual in its internal grid. The intent is to have small residual, which make easier to
compute the _inverse_ transformation (given a latitude and longitude, find indices of the
pixel at that location). However if the localization grid is non-linear, then the affine transform
is a poor approximation of that grid and the residuals are high. High residual make _inverse_
transforms hard to compute, which result sometime in {{TransformException}} being throw with
a "no convergence" error message.

In practice, the localization grid in netCDF files is often used for storing the results of
a map projection. The Mercator projection for example is often used. The proposed fix is to
allow {{LocalizationGridBuilder}} to try to transform the grid using a given list of map projections
and see if one of those projections results in a grid closer to a linear transform. In other
words, we should be able to "guess" what the projection may be. It is okay if the guess is
not a perfect match; if the residuals become smalls, it will resolve the "no convergence"
errors.



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