Discussions with https://github.com/Ptychography-4-0/ptychography/ team:

Ptychography reconstruction requires partial reconstruction and stitching of regions that are close and compact in sample coordinates and not necessarily in the "natural order" and current partitioning of the dataset, which could be a random scan with temporal ordering.

To enable distributed ptychography, it should be possible to run an UDF in such a way that data that belongs to a global ROI is passed as one data block to a reconstruction algorithm, i.e. "process_partition()" The local result is then merged into a global result buffer with a non-trivial merge function.

The actual reconstruction and merge can be swapped out as needed and the size and shape of regions can be adapted to the "sweet spot" of various algorithms and hardware as needed.