gr2stn()

This function is a grid-to-station interpolator. It creates "station" data by taking a 1-dimensional sample from a gridded data set and interpolating to a given location. That location may be provided by specifying a longitude and a latitude, or by providing a station expression.

gr2stn(grid_expr, lon, lat <,-a>)
or
gr2stn(grid_expr, stn_expr <,-a>)

where:

grid_expr is a GrADS expression that gives a grid result. The interpolation will be done on this data.

stn_expr is a GrADS expression that gives a station data result. The interpolation will be done to the station location, the value of the station data is not used.

lon,lat may be used instead of stn_expr to specify the location to which the gridded data will be interpolated.

Usage Notes

1. The interpolation will work when only one dimension is varying (either Z or T).

2. The result of the function is station data. The interpolation is done bi-linearly within the grid space. No weighting is done to account for real-world coordinate systems.

3. Use the -a option to return a value even if the location is not completely surrounded by grid points.

4. See the section of the User's Guide on Arbitrary Cross Sections for more information on applications of gr2stn.

   Examples

   1. To examine the difference between an analysis (ie, gridded data) and the original observations, one could:
      d t.3-gr2stn(t.1,t.3)

      where file 1 is gridded data, and file 3 is station data. The result would displayas differences at the station locations.

      If one wanted to display the difference calculated in Example 1 as a contour field, one can use the oacres function to do a quick analysis of the station values:

      d oacres(t.1,t.3-gr2stn(t.1,t.3))