Spacing is not taken in account when plotting a 1D vtkImageData in a 2D chart (e.g. Line Chart View)
The title says it all. I think the same applies for the "origin".
X axis labels don't take in account the spacing and origin.
A fix can be added in int vtkChartRepresentation::RequestData. But it's not an easy task apparently.
There's also vtkDataObject* vtkChartRepresentation::TransformInputData, where input data can be changed before plotting it.