[vtkusers] PCA statistics change

[David Thompson]

Hi all,

Recently, Ben switched VTK to use Eigen's singular value decomposition. It reports some eigenvectors flipped. Notably, it seems to prefer a right-handed coordinate system as its output basis in 3D. This is great! ... but note that image tests that plot assessed values (i.e., the inputs projected into the new basis) may now return different results with the y axis assessed-value flipped.

Does anyone know if the VTKExamples repo does image-based tests? If so, I expect that may be causing a failure. However, it is unclear from the test output[1] whether an OpenGL/machine configuration error is masking an image test failure.

    Thanks,
    David

[1]: https://open.cdash.org/testDetails.php?test=623072463&build=5241493
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