The API endpoint "/wthr/svar/InterpolatedData" returns the value of a variable for a specified position and time. If you need the values of different variables and/or times, please use the API endpoint /get_timeseries. The returned value will be bilinear interpolated from the grid points of the forecast model around the values for the returned position. At Wikipedia you find a good expanation of the bilinear interpolation: Wikipedia - Bilinear interpolation
curl --location -g --request GET 'weather.openportguide.org/api/wthr/svar/InterpolatedData?variable=TMP&latitude=54&longitude=9&apiKey={{api-key}}' \
--header 'Host: {{BASE_URL}}' \
--header 'x-api-key: {{api-key}}'
{"metadata":{"serviceProvider":"navapi.com","originatingCenter":"US National Weather Service - NCEP (WMC)","generatingProcess":"Global Forecast System Model","model":"gfs","requestedParameters":"model=None, variable=ICETMP, level=None, latitude=-70, longitude=-15, timestep=None, units=None","shortName":"ICETMP","fullName":"Ice Temperature","unit":"°C","level":"surface","ny":721,"nx":1440,"latitudeFirstGridpoint":90.0,"latitudeLastGridpoint":-90.0,"longitudeFirstGridpoint":0.0,"longitudeLastGridpoint":359.75,"gridlengthXDirection":0.25,"gridlengthYDirection":-0.25,"refDate":"2025-06-25T12:00:00Z","forecastTime":[0,"2025-06-25T12:00:00Z"],"forecastPosition":[{"latitude":-70.0},{"longitude":-15.0}],"UsedTokens":1},"data":{"value":-31.4}}