WeatherSampler does not work when Weather is enabled

[BrianCollinss]

What happened?

• When I have both WeatherSampler and Weather enabled, the sims are not random and always depend on the Weather's met file.
• When Weather is disabled, I get all sorts of errors as many underlying processes rely on Weather. For example:

Unable to evaluate linear interpolation function .Simulation.Field.Maize.Leaf.FrostFraction --> Error while locating variable '[Weather].MinT' in variable reference '.Simulation.Field.Maize.Leaf.FrostFraction.XValue' --> Unable to find any model with name or type Weather in scope of XValue

What Operating System are you on?

Windows

[ric394]

From my limited understanding of WeatherSampler it's main usage is related to Simulation spin up.
Are you trying to do something similar?

[BrianCollinss]

I am studying it for the first time as we're thinking of building a new weather-related model. I added it next to Weather and expected to see different results each time I run the sims, but it didn't happen as Weather data was always used instead. Perhaps I'm using it wrongly.

[sno036]

@BrianCollinss - WeatherSampler is instead of Weather not as well as. So this is expected behaviour - although it might be better if it threw a fatal error if both were in the simulation.

[BrianCollinss]

Thanks @sno036 but when I remove weather, it throws as Maize, for example, calls it.

[hol353]

The problem is that lots of models in APSIM look for a model called 'Weather'. They shouldn't, but they do.

The workaround might be to remove Weather and rename WeatherSampler to weather in the GUI.

On this PR (#9326) I talk about wanting to refactor the messy weather components. One day...

[BrianCollinss]

Thanks @hol353. What do you recommend models do if they need access to daily weather data?

[hol353]

They should [Link] to IWeather, rather than [Weather]. This way, it doesn't matter what the name or type of the weather model is, just that it implements an IWeather interface. A lot of models already do this, but as you've discovered, not all.

[rcichota]

I also noticed that WeatherSampler does not have all the outputs that Weather has (this may add to the errors you're having). I will try finishing that pull request ensuring that both models have the same variables (and defaults). Refactoring might need a bit more time/focus.