Write a derived product¶

A component computing something from a finished acquisition, such as a median or a mask, writes it against the store the device wrote. The acquisition belongs to the service and its device (ADR 0013); a derived product is the one thing redsun writes.

Install the extra¶

pip install redsun[zarr]

Without it, a writer raises WriterError naming the extra.

Pick the writer by mimetype¶

The StreamResource document names the format and the store:

from redsun.storage.writers import ome_zarr


def on_stop(self, resource: StreamResource, median: NDArray[np.uint16]) -> None:
    if resource["mimetype"] != "application/x-ome-zarr":
        self.logger.warning(f"Cannot write a median into {resource['mimetype']!r}.")
        return
    product_uri = ome_zarr.write(
        resource["uri"],
        data_key="det_median",
        data=median,
        metadata={"derived_from": resource["data_key"]},
    )

Every writer takes the same arguments, named after the document's fields:

def write(
    uri: str,
    *,
    data_key: str,
    data: NDArray[Any],
    metadata: Mapping[str, Any] | None = None,
) -> str: ...

zarr writes application/x-zarr, ome_zarr writes application/x-ome-zarr.

Read the returned URI¶

The writer reads the store and decides where the product goes; the return value says where:

Adding a key to a root with OME-Zarr metadata drops its ome block, so ome_zarr.write writes a sibling and zarr.write refuses the store.

Metadata goes to the product's own group, never the root: a stream closing on the store rewrites the root's metadata.

Register it, or not¶

A writer registers nothing. A product that belongs in a catalog is put there by the same callback; the two are separate choices.