Switch association mechanism for forecast data to city to use bilinear interpolation

[amehta-scottlogic]

Description

Mentors have said they currently use bilinear interpolation on a city's coordinates to calculate the pollutant values to use from forecast data.

At the moment we're using nearest, so let's change it to be in sync

Acceptance Criteria

• We use bilinear interpolation as the method to associated city with pollutant forecast data

Test Checklist:

• [x] Test Analysis & discussion with developer
• [x] Write Test Cases / Charters
• [x] Test Cases & Charters Reviewed
• [ ] Test Cases / Charters Executed
• [x] Regression tests executed
• [ ] Write Automation tests for regression

[mwalker-scottlogic]

Test Analysis

• The objective is not to test the Xarray interp() function as this is not our code
• Need to establish if we are using interp() correctly, have asked @sebsteinig to confirm
• To test:
  • For a given ECMWF lat lon for a city, and using the same CAMS data, our forecast database data should match the forecast data released by ECMWF here
  • This would implicitly test the bilinear interpolation as both data should be using bilinear interpolation, and if it was being calculated incorrectly the data would not match

Test Case required:

• Verify data in forecast database matches ECMWF forecast
• #3.xlsx
  • Candidate for automation: Yes (when there is a deployed env)

Test Charter

• Explore forecast database with reference to latest air quality forecasts for the list of the CNN cities to discover if pollutant values are correct for given cities.

[mwalker-scottlogic]

Only regression tested forecast db as in_situ is too unstable

[mwalker-scottlogic]

This can't be tested until the bug is fixed here https://github.com/orgs/ECMWFCode4Earth/projects/12/views/1?pane=issue&itemId=63508204