GDAL reader is incomplete
From @john.tourtellott :
In general, GDAL images contain a geotransform that can include rotation and skewing, such that there is no real up and down. The current reader doesn't address the general case, but instead presumes the image is aligned to north-south and east-west, and uses the origin and spacing to represent the mapping from image to geomap coordinates. (And since the GDAL origin is top-left, this creates a negative spacing in the y component, which doesn't always "work" with vtk filters.)
If we make this change, we'll also need to update vtkMap, which does conversions between vtkUniformGrid and GDALDataset as part of reprojecting input data to display coordinates. Not a big deal, but we should coordinate effort.
Also, if we want to proceed with the MR, I would suggest we make the proposed row and spacing inversion an option, so that users who want to retain the current/native format can do so.
I also now realize that I should have included the input geotransform as field data in the vtkUniformGrid.
It also might be worth discussing whether vtkUniformGrid is the right representation for GDAL data. Maybe there should be a new vtkDataSet subclass for more-general cases (vtkRasterDataSet?).