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Fix vtk mrml double array storage node reader writer

Sam Horvath requested to merge github/fork/jcfr/fix-vtkMRMLDoubleArrayStorageNode-reader-writer into master

Created by: jcfr

The reader in vtkMRMLDoubleArrayStorage was always setting the first line of values in the .mcsv file as labels. If the stored vtkMRMLDoubleArray had not labels set, then the retrieved double array labels would be set to the first line of numerical values, associated with the first data point. This resulted in a missing data point as well as shifted indices for all remaining points, and incorrect labels.

The correction this commit offers is to write the line '# nolabels' in the file if labels exist. If the reader finds this line, it will set the first line of values as the first data point, instead of setting it as label values.

Examples :

Here are four examples with (u,v,w) as labels, (12.1,425.577,-454) for the first data point, and (8.79633e+09,0,-1) for the second one:

(1) New writer: vtkMRMLDoubleArrayNode with labels

   # measurement file filename.mcsv
   u,v,w
   12.1,425.577,-454
   8.79633e+09,0,-1

(2) New writer: vtkMRMLDoubleArrayNode with no labels set

   # measurement file filename.mcsv
   # nolabels
   12.1,425.577,-454
   8.79633e+09,0,-1

(3) Old writer: vtkMRMLDoubleArrayNode with labels

   # measurement file filename.mcsv
   # columns = x,y,yerr
   u,v,w
   12.1,425.577,-454
   8.79633e+09,0,-1

(4) Old writer: vtkMRMLDoubleArrayNode with no labels set

   # measurement file filename.mcsv
   # columns = x,y,yerr
   12.1,425.577,-454
   8.79633e+09,0,-1

Observations :

The line '# columns = x,y,yerr' was hardcoded [1] in the former writer and had no meaning related to the actual double array node labels. The inspiration problably came from .mcsv or .acsv writers/readers [2][3] but had no effect here.

[1] https://github.com/Slicer/Slicer/blob/6e63b4bf5dbc65a9973160de7397dfc47882e038/Libs/MRML/Core/vtkMRMLDoubleArrayStorageNode.cxx#L244 [2] https://github.com/Slicer/Slicer/blob/master/Modules/Loadable/Markups/MRML/vtkMRMLMarkupsFiducialStorageNode.cxx#L159-L185 [3] https://github.com/Slicer/Slicer/blob/master/Modules/Loadable/Annotations/MRML/vtkMRMLAnnotationFiducialsStorageNode.cxx#L245-L268

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