Bugfix: Invalid latitude values from a MPAS file

[hsoh-u]

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Describe the Problem

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MET reads latitude and longitude variables as double-precision values regardless of their original data type, converting float values to double precision during processing. Converting radian values as latitude values from float to double precision can introduce rounding errors, potentially resulting in values exceeding 90.0° or dropping below −90.0° when processing MPAS files.

Below is an example error message

DEBUG 6: get_nc_data(NcVar *, double *) lonCell data_size=41943042, is_unsigned_value: 0
DEBUG 6: UGridFile::read_netcdf_grid() -> convert  rad to degree for lat
DEBUG 6: UGridFile::read_netcdf_grid() ->   convert rad to degree for lon
DEBUG 9: UnstructuredData::set_points(int, double *, double *) first (-89.95510084, -58.29018675) and last (20.91506741, -0.01718597825) from (-89.95510084, -58.29018675) and (20.91506741, -0.01718597825)
PRE-MAIN-ERROR Exception: BadValue: Invalid latitude -90.000002504478161  (/glade/work/dtcrt/METplus/casper/components/MET/installations/12.2.0/external_libs/eckit/eckit-1.24.4/src/eckit/geometry/CoordinateHelpers.cc +49 assert_latitude_range)
terminate called after throwing an instance of 'eckit::BadValue'
  what():  BadValue: Invalid latitude -90.000002504478161
FATAL: Received Signal Abort. Exiting 6

The sample files and scripts are prepared at (/glade/u/home/johnhg/work/METplus/discussions/falko_20260422, casper or derecho) by @JohnHalleyGotway.

The coordinate NetCDF file ens_1/init.nc contains float data type radian values for lat and lon variables.

       float latCell(nCells) ;
                latCell:units = "rad" ;
                latCell:long_name = "Latitude of cells" ;
        float lonCell(nCells) ;
                lonCell:units = "rad" ;
                lonCell:long_name = "Longitude of cells" ;

Here are max and min radian values in the NetCDF file:

ncdump -v latCell ens_1/[init.nc](http://init.nc/) | grep "1\.57079" 
   -0.9446307, -1.570237, -1.570796, -1.570183, -1.569678, -1.569795,
    0.9437245, 0.944019, 0.9440414, 0.9443362, 0.9446307, 1.570237, 1.570796,

float data type minimum radian -1.570796 == -89.999981276
float data type maximum radian 1.570796 == 89.999981276
double data type minimum radian -1.570796371 == -90.000002532989
double data type maximum radian 1.570796371 == 90.000002532989

Expected Behavior

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The converted latitude values (from the radian unit) should be adjusted to remain within the −90.0° to 90.0° range.

Environment

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1. casper or derecho
2. OS: (e.g. RedHat Linux, MacOS)
3. MET12.2.0 and MET13.0.0

To Reproduce

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1. login to casper or derecho
2. change directory to /glade/u/home/johnhg/work/METplus/discussions/falko_20260422
3. ./run_ps.sh

Relevant Deadlines

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Funding Source

NCAR base 2702701

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