Average over shape process

[huard]

Description

Given one or multiple polygons and a netCDF file, compute the spatial average (area-weighted) over each region and store along a new "geometry" dimension.

Might require to pass a file storing the cell area for accurate computations.

[richardarsenault]

@huard , this is in finch, but we now have a basic averaging method using rioxarray to do simple averaging at the catchment scale. Is this something that has advanced and/or reasonable to think that we can get it rolled-out in the next 3 months?

[huard]

Yes, it's part of my master plan. Will probably use new functionality just released in xESMF however. Once the weights are computed, this is really fast. See https://pangeo-xesmf.readthedocs.io/en/latest/notebooks/Spatial_Averaging.html

• Implement in xESMF
• Wrap in clisops Spatial averaging over polygons roocs/clisops#38
• Wrap in finch
• Use in raven workflows

[rsignell-usgs]

@huard is there a nice "real life use case" notebook that demonstrates this capability I could use for a demo?

[huard]

https://pavics-sdi.readthedocs.io/en/latest/notebooks/regridding.html#Fourth-example-:-Averaging-over-polygons
https://pangeo-xesmf.readthedocs.io/en/latest/notebooks/Spatial_Averaging.html

[rsignell-usgs]

@huard , Is there a python example that would make the polygon request and retrieve the output using this new Finch WPS service?

Or am I not understanding the capabilities?

[huard]

@aulemahal I don't think that apart from the unit test, we've gotten there yet, correct ?

@rsignell-usgs Yes, this is correct. I've created an issue to do this. #165 We probably won't be able to get this done until April though. If you want to try your hand,

1. install the birdy client: https://github.com/bird-house/birdy
2. connect to the finch server and call the average_polygon method:

from birdy import WPSClient
url = 'https://pavics.ouranos.ca/twitcher/ows/proxy/finch/wps'
wps = WPSClient(url)
wps.average_polygon?

[aulemahal]

True, there is no example of the use of this process.

[aulemahal]

Oh haha, not a real example, but I had an issue with subset_polygon here : #153 (comment)
If I coded this correctly, change subset to average and you have a minimal example.

[rsignell-usgs]

@huard and @aulemahal, I gave it a try, and was able to submit and process a non-polygon request, but failing with polygon request. I'm sure it's user error:
https://nbviewer.jupyter.org/gist/rsignell-usgs/10059fde7b80d8c29f962505ab024b10

[huard]

Try with an absolute file name for the geojson polygon. Otherwise, the client will assume you're passing the geojson object as a string representation. The client could probably be made smarter eventually...