data at 1 point

[Jennifer Adams]

Matt,
The problem is that your grid resolution is too high. A grid increment
of 0.001 degrees is too small for GrADS to resolve properly -- world
coordinates are carried around as floats, not doubles. This isn't so
much of an issue when you're displaying a lat/lon plot, because the
edges of the domain get clipped at the graphics stage, but if you're
trying to extract a single grid point, it exposes this problem rather
effectively.
Jennifer



On Feb 10, 2005, at 11:13 AM, Matt Alonso wrote:

> Howdy folks,
>
> I am really at a complete loss on this one.  I am trying to get the
> value at one particular point.  In the past anytime I wanted to do this
> I have always done:
>
> set x 3
> set y 3
> d a1
>
> I am working with model output data that I have worked with a 1000
> times before.  This is the output from the session:
>
> ga-> open 127_K.ctl
> Scanning description file:  127_K.ctl
> Data file 127_K.dat is open as file 1
> LON set to -121.77 -121.629
> LAT set to 37.7194 37.831
> LEV set to 1000 1000
> Time values set: 2004:1:26:0 2004:1:26:0
> ga-> set x 2
> LON set to -121.769 -121.769
> ga-> set y 2
> LAT set to 37.7203 37.7203
> ga-> d a1
> Data Request Error: Invalid grid coordinates
>  World coordinates convert to non-integer grid coordinates
>    Variable = a1  Dimension = 0
>  Error ocurred at column 1
> DISPLAY error:  Invalid expression
>  Expression = a1
> ga-> set x 2 3
> LON set to -121.769 -121.768
> ga-> d a1
> ga->
>
> I am sure this is just something that I am screwing up, but I cannot
> seem to figure this one out.  As long as either X or Y has more than
> one point it works fine.  What am I doing wrong?  Thanks in advance.
>
> Matt
>
>
--
Jennifer Miletta Adams
IGES/COLA
4041 Powder Mill Rd., Suite 302
Calverton, MD 20705