issues: 118910006

Most of the netCDF data I work with stores, in addition to the coordinates themselves, the bounds of each coordinate value. Often these bounds are stored as arrays with shape Nx2, where N is the number of points for that coordinate. For example:

``` $ ncdump -c /archive/Spencer.Hill/am3/am3clim_hurrell/gfdl.ncrc2-intel-prod-openmp/pp/atmos/ts/monthly/1yr/atmos.201001-201012.t_surf.nc netcdf atmos.201001-201012.t_surf { dimensions: time = UNLIMITED ; // (12 currently) lat = 90 ; bnds = 2 ; lon = 144 ; variables: double average_DT(time) ; average_DT:long_name = "Length of average period" ; average_DT:units = "days" ; average_DT:missing_value = 1.e+20 ; average_DT:_FillValue = 1.e+20 ; double average_T1(time) ; average_T1:long_name = "Start time for average period" ; average_T1:units = "days since 1980-01-01 00:00:00" ; average_T1:missing_value = 1.e+20 ; average_T1:_FillValue = 1.e+20 ; double average_T2(time) ; average_T2:long_name = "End time for average period" ; average_T2:units = "days since 1980-01-01 00:00:00" ; average_T2:missing_value = 1.e+20 ; average_T2:_FillValue = 1.e+20 ; double lat(lat) ; lat:long_name = "latitude" ; lat:units = "degrees_N" ; lat:cartesian_axis = "Y" ; lat:bounds = "lat_bnds" ; double lat_bnds(lat, bnds) ; lat_bnds:long_name = "latitude bounds" ; lat_bnds:units = "degrees_N" ; lat_bnds:cartesian_axis = "Y" ; double lon(lon) ; lon:long_name = "longitude" ; lon:units = "degrees_E" ; lon:cartesian_axis = "X" ; lon:bounds = "lon_bnds" ; double lon_bnds(lon, bnds) ; lon_bnds:long_name = "longitude bounds" ; lon_bnds:units = "degrees_E" ; lon_bnds:cartesian_axis = "X" ; float t_surf(time, lat, lon) ; t_surf:long_name = "surface temperature" ; t_surf:units = "deg_k" ; t_surf:valid_range = 100.f, 400.f ; t_surf:missing_value = 1.e+20f ; t_surf:_FillValue = 1.e+20f ; t_surf:cell_methods = "time: mean" ; t_surf:time_avg_info = "average_T1,average_T2,average_DT" ; t_surf:interp_method = "conserve_order2" ; double time(time) ; time:long_name = "time" ; time:units = "days since 1980-01-01 00:00:00" ; time:cartesian_axis = "T" ; time:calendar_type = "JULIAN" ; time:calendar = "JULIAN" ; time:bounds = "time_bounds" ; double time_bounds(time, bnds) ; time_bounds:long_name = "time axis boundaries" ; time_bounds:units = "days" ; time_bounds:missing_value = 1.e+20 ; time_bounds:_FillValue = 1.e+20 ;

// global attributes: :filename = "atmos.201001-201012.t_surf.nc" ; :title = "am3clim_hurrell" ; :grid_type = "mosaic" ; :grid_tile = "1" ; :comment = "pressure level interpolator, version 3.0, precision=double" ; :history = "fregrid --input_mosaic atmos_mosaic.nc --input_file 20100101.atmos_month --interp_method conserve_order2 --remap_file .fregrid_remap_file_144_by_90 --nlon 144 --nlat 90 --scalar_field (please see the field list in this file)" ; :code_version = "$Name: fre-nctools-bronx-7 $" ; data:

lat = -89, -87, -85, -83, -81, -79, -77, -75, -73, -71, -69, -67, -65, -63, -61, -59, -57, -55, -53, -51, -49, -47, -45, -43, -41, -39, -37, -35, -33, -31, -29, -27, -25, -23, -21, -19, -17, -15, -13, -11, -9, -7, -5, -3, -1, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89 ;

lon = 1.25, 3.75, 6.25, 8.75, 11.25, 13.75, 16.25, 18.75, 21.25, 23.75, 26.25, 28.75, 31.25, 33.75, 36.25, 38.75, 41.25, 43.75, 46.25, 48.75, 51.25, 53.75, 56.25, 58.75, 61.25, 63.75, 66.25, 68.75, 71.25, 73.75, 76.25, 78.75, 81.25, 83.75, 86.25, 88.75, 91.25, 93.75, 96.25, 98.75, 101.25, 103.75, 106.25, 108.75, 111.25, 113.75, 116.25, 118.75, 121.25, 123.75, 126.25, 128.75, 131.25, 133.75, 136.25, 138.75, 141.25, 143.75, 146.25, 148.75, 151.25, 153.75, 156.25, 158.75, 161.25, 163.75, 166.25, 168.75, 171.25, 173.75, 176.25, 178.75, 181.25, 183.75, 186.25, 188.75, 191.25, 193.75, 196.25, 198.75, 201.25, 203.75, 206.25, 208.75, 211.25, 213.75, 216.25, 218.75, 221.25, 223.75, 226.25, 228.75, 231.25, 233.75, 236.25, 238.75, 241.25, 243.75, 246.25, 248.75, 251.25, 253.75, 256.25, 258.75, 261.25, 263.75, 266.25, 268.75, 271.25, 273.75, 276.25, 278.75, 281.25, 283.75, 286.25, 288.75, 291.25, 293.75, 296.25, 298.75, 301.25, 303.75, 306.25, 308.75, 311.25, 313.75, 316.25, 318.75, 321.25, 323.75, 326.25, 328.75, 331.25, 333.75, 336.25, 338.75, 341.25, 343.75, 346.25, 348.75, 351.25, 353.75, 356.25, 358.75 ;

time = 10973.5, 11003, 11032.5, 11063, 11093.5, 11124, 11154.5, 11185.5, 11216, 11246.5, 11277, 11307.5 ; } ```

These 2-D bounding arrays lead to the "Buffer has wrong number of dimensions" error in #665. In the case of #665, only the time coordinate has this 2-D bounds array; here other coordinates (namely lat and lon) have it as well.

Conceptually, these bound arrays represent coordinates, but when read in as a Dataset, they become variables, not coordinates. Perhaps this is part of the problem?