VTK Unstructured Grid and Higher Order Lagrange Elements

Hello, I’m trying to write higher order lagrange elements to VTK’s unstructured grid format. Based on the format, it seems like there needs to be direct correspondence between the values of the single allowed data array in and the values in any data array in . This seems to mean that all cells in the grid must be isoparametric (the dimensions of mapping space and value space are the same).

Is this accurate? If so, it feels kind of wasteful. Is there some work around that can be employed to save space?