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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