Describe the Enhancement

This feature request arose via met-help for a NASA user:
https://rt.rap.ucar.edu/rt/Ticket/Display.html?id=100072
While this idea arose via met-help, it would be widely useful.

When reading gridded data from NetCDF the level string defines how to index into the variable dimensions to extract the 2D field of data. For example:

name = "varname"; level = "(0,4,*,*)";

The *,* indicates the gridded dimensions, and the 0,4 indicates that the 0-th index from the first dimension and 4-th index from the second dimension should be used.

MET's NetCDF library code includes a special case for the "time" dimension. Instead of an integer index value, the user can supply a timestring in YYYYMMDD[_HH[MMSS]] format. The NetCDF library code parses the timestamp, searches the time dimension for that time, and then uses the index for that matching value.

This issue is to extend that same logic to non-time dimensions as well. For example, let's say there is a coordinate variable named "pressure", meaning there is both a variable and dimension named pressure. For example:

name = "varname"; level = "(550,d02,*,*)"; // for varname(pressure,domain,Nx,Ny)

The logic should be:

• For "550" in the first dimension, search the "pressure" coordinate variable to find the matching index.
• For "d02" in the second dimension, search the "domain" coordinate variable to find the matching index.

If either value is not found, error out with a useful error message.

The big challenge here is that 550 is an integer. So it could conceivably either specify a coordinate variable VALUE or an INDEX. The difficulty is distinguishing between them. We could consider supporting embedded single or double quotes to differentiate between strings and indices. For example:

name = "varname"; level= "(550,'d02',*,*)"; // 550 is an index
name = "varname"; level = "('550','d02',*,*)"; // 550 is a pressure level value

Recommend that we think more about this.

Time Estimate

3 days.

Sub-Issues

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No sub-issues needed.

Relevant Deadlines

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Funding Source

2799991

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• METplus, MET, METdatadb, METviewer, METexpress, METcalcpy, METplotpy
  Will likely need a METplus issue to support the use of this new option.

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