20060314: computing a parameter at a single location

On Tue, 2006-03-14 at 09:21, address@hidden wrote:
> I need to be able to compute the gradient between two points for which I
> will only know the lat/lon values.  I'm looking for the easiest way to do
> this.  Is there a way to spit out the value for a parameter by providing a
> single lat/lon? 

Matt,

Yes, you could use the GDPOINT program to output a value at a specific
GPOINT. You can also use the ddx(), ddy(), and/or grad() grid
diagnostics at an intervening lat/lon.

> Or alternatively, is there a simple way of obtaining the
> actual gridpoints for a location if I only know the latitude/longitude
> coordinates so that I can easily reference the grid points in a Fortran
> program?

The GEMPAK library provides a function GR_PLOC that accepts the
character string for GPOINT (which may be grid point locations,
lat/lon, station id etc), and provides back the projected grid
point location as well as lat/lon values (you could add a write(*,*)
statement tothe $NAWIPS/comet/gdpoint/gdpoint.f routine to
output the rgy and rgy location following the GR_PLOC call if
you wanted to use that program as a starting point).

Steve Chiswell
Unidata User Support
> 
> Matt Borkowski
> Graduate Student
> North Carolina State University
> Department of Marine, Earth, and Atmospheric Science
>