I’m not sure if vtkImageDataGeometryFilter is designed to work with cell data, unfortunately it’s a filter that I’m not familiar with. In general a “vtkImageData” is used to store the data values for a regular grid of points (e.g. via GetPointData().SetScalars()), and then other filters and mappers will interpolate to get the values beween the points. This is e.g. how contouring and volume rendering works with images in VTK.