Use mesh2d_bldepth instead of mesh2d_flowelem_bl for get_Dataset_atdepths if available in conventions

[veenstrajelmer]

In case of zsigma-layer model with minimal layer definition, we have the variable mesh2d_bldepth from the get_formula_terms["depth"]. In that case we do not need mesh2d_flowelem_bl anymore (for which we are also not sure if it is in the model output). Nevertheless, dfmt.get_Dataset_atdepths() raises KeyError: 'get_Dataset_atdepths() called with reference=bedlevel, but mesh2d_flowelem_bl variable not present' when slicing with reference bedlevel.

import dfm_tools as dfmt

file_nc = r"p:\11209731-002-nutrient-reduction-ta\runs_OSPAR\B05_waq_withDOM_2016\DFM_OUTPUT_DCSM-FM_0_5nm_waq\DCSM-FM_0_5nm_waq_0000_map.nc"

uds = dfmt.open_partitioned_dataset(file_nc)

uds_sel = uds[['mesh2d_taus', 'mesh2d_tausx', 'mesh2d_tausy', 'mesh2d_ucx', 'mesh2d_ucy', 
               "mesh2d_s1", "mesh2d_bldepth", "mesh2d_sigmazdepth", "mesh2d_interface_z", "mesh2d_interface_sigma",
               'mesh2d_layer_sigma', 'mesh2d_layer_z', "mesh2d_layer_sigma_z", "mesh2d_interface_sigma_z", 
               ]]

ds_depth = dfmt.get_Dataset_atdepths(uds_sel, depths=[-1], reference='bedlevel')

We can get the "mesh2d_bldepth" variable with:

from dfm_tools.get_nc import get_formula_terms
depthvar = get_formula_terms(uds, 'layer')['depth']

But it is important to note that positive is down instead of up, so multiply with -1