3D extraction across times at given depth

[raymondben]

Probably related to #5.
romsdata3d will extract xyz data (2D at all depths for a given time index). There is an equivalent extraction (2D data at all times for a given depth index) for which angstroms doesn't have a convenience wrapper, but which would be handy.

[mdsumner]

Huh, good point - it only needs lvar = 3L to be available as an option, can you experiment with lvar-3 branch?

https://github.com/hypertidy/angstroms/blob/lvar-3/R/romsdata.R#L113

(brick doesn't handle the more general case, so lvar can't be 1 or 2 ... so doing this properly needs some attention)

[raymondben]

That works a treat.

[mdsumner]

Now in master c0f450d

😨 ... should the first layer be the surface or the bottom? ...

I've set it up to match what I had before, i.e. layer 1 is the surface, and this matches the other conventions for slicing.