load_stac: custom item filter/transform

[jdries]

Proposed Process ID: load_stac
Proposed Parameter Name: item_callback
Optional: yes, default: None

Context

Our users want rather complex filters on STAC items before loading them.
For instance: when loading sentinel-1 GRD and the temporal coverage is high, meaning 2 or more items per 10 days, then they want to filter out more items:

• either randomly selecting
• or by selecting a certain orbit direction

Description

This parameter allows to provide a process graph that will filter the whole STAC ItemCollection that is the result of the STAC query.
The return type of the process graph is a STAC Item Collection, potentially modified.

Data Type

process graph

[m-mohr]

Why is this not feasible with the properties parameter?

[jdries]

The properties parameter is constrained to return true or false for individual values, the callback process does not receive any context about the item the value belongs to or the total list of items that satisfy the other constraints.

[m-mohr]

Maybe I don't fully understand the usecase yet, but for example the usecase "selecting a certain orbit direction" is totally possible right now:

"sat:orbit_state": eq(value, "ascending")

If you'd want to work on STAC objects or even ItemCollections in a process graph, we'd need processes that work on objects in openEO, otherwise you can't even extract e.g. sat:orbit_state from the STAC properties without a UDF. So the parameter could only be used with UDFs right now, which for me seems to much of an edge case to have in the process definition by default for everyone to implement.

Are there potential alternatives e.g. via datacube dimensions or so?