Questions about grid files

[JDTilley]

So I've managed to get ROMS installed and run multiple test cases. So now I am trying to take the next step and run the model for my study area. I am trying to build a netcdf file in Python, but there are a few things I'm not sure about.

First, what is the spherical variable? I'm only trying to make a standard rectangular grid. I'm not sure what I should put in this variable or what dimensions.

Second, I see xl and el as domain length in the XI-direction and ETA-direction, respectively. What would my domain be based off of. Would it be the extent of the rho points or psi points, and should I include the boundary?

The angle I'm assuming should be zero in my case since I want a simple rectangular grid (parallel to lines of latitude and longitude); however, I'm not sure what curvilinear coordinate metric in XI and ETA means. I don't understand what xi/eta derivative of inverse metric factor pn/pm means either. It would be nice if I could just fill all this with zeros.

Finally, I don't understand what the difference is between 'Final bathymetry' and 'Working bathymetry'. I know its a lot of questions, but if I can get some guidance on these details I should hopefully be on my way to creating my first grid file. Thanks.

[kate]

So I've managed to get ROMS installed and run multiple test cases. So now I am trying to take the next step and run the model for my study area. I am trying to build a netcdf file in Python, but there are a few things I'm not sure about.

First, what is the spherical variable? I'm only trying to make a standard rectangular grid. I'm not sure what I should put in this variable or what dimensions.

This is a single value, either true or false (1 or 0). For a simple rectangular grid, you can set it to 0 and provide the model with the x_rho, y_rho etc. variables instead of lat_rho, lon_rho (and all the rest).

Second, I see xl and el as domain length in the XI-direction and ETA-direction, respectively. What would my domain be based off of. Would it be the extent of the rho points or psi points, and should I include the boundary?

ROMS itself will ignore these. There might be plotting code that uses them. They are used in ana_grid and refer to the dimensions of the psi-point boundaries.

The angle I'm assuming should be zero in my case since I want a simple rectangular grid (parallel to lines of latitude and longitude); however, I'm not sure what curvilinear coordinate metric in XI and ETA means. I don't understand what xi/eta derivative of inverse metric factor pn/pm means either. It would be nice if I could just fill all this with zeros.

For a truly lat,lon grid on a sphere, the d pm/dy variable would be non-zero, but for a rectangular grid, they can all be zero.

Finally, I don't understand what the difference is between 'Final bathymetry' and 'Working bathymetry'. I know its a lot of questions, but if I can get some guidance on these details I should hopefully be on my way to creating my first grid file. Thanks.

ROMS only reads the "h" variable and ignores "hraw". I use hraw for holding various versions of unclipped, unsmoothed and clipped, smoothed bathymetries.

[JDTilley]

Wow. Thanks so much for all the great information!