The latitude and longitude coordinates of a horizontal grid that was
not defined as a Cartesian product of latitude and longitude axes,
can sometimes be represented using two-dimensional coordinate variables.
These variables are identified as coordinates by use of
the coordinates attribute.
Example 5.2. Two-dimensional coordinate variables
dimensions:
xc = 128 ;
yc = 64 ;
lev = 18 ;
variables:
float T(lev,yc,xc) ;
T:long_name = "temperature" ;
T:units = "K" ;
T:coordinates = "lon lat" ;
float xc(xc) ;
xc:long_name = "x-coordinate in Cartesian system" ;
xc:units = "m" ;
float yc(yc) ;
yc:long_name = "y-coordinate in Cartesian system" ;
yc:units = "m" ;
float lev(lev) ;
lev:long_name = "pressure level" ;
lev:units = "hPa" ;
float lon(yc,xc) ;
lon:long_name = "longitude" ;
lon:units = "degrees_east" ;
float lat(yc,xc) ;
lat:long_name = "latitude" ;
lat:units = "degrees_north" ;
T(k,j,i) is associated with the coordinate
values lon(j,i), lat(j,i),
and lev(k). The vertical coordinate is represented
by the coordinate variable lev(lev) and the
latitude and longitude coordinates are represented by the auxiliary
coordinate variables lat(yc,xc) and
lon(yc,xc) which are identified by the
coordinates attribute.
Note that coordinate variables are also defined for the
xc and yc dimensions.
This faciliates processing of this data by generic applications
that don't recognize the multidimensional latitude and longitude
coordinates.