data at 1 point

[Matthias Munnich]

Thus an easy way to circumvent your problem is to lie to GrADS in
another descriptor file for your data. In it multiply  DLON in the XDEF
record (XDEF N LINEAR LON0 DLON) by 1000. The world coordinates will be
wrong, but for a time series plot at a single point you don't care.

Matt

Jennifer Adams wrote:
> 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
>
>

--
-----------------------------------------
Matthias Munnich
Univ. of California, Los Angeles
Inst. of Geophysics and Planetary Physics
and Dep. of Atmos. and Oceanic Sciences
3845 Slichter Hall
Los Angeles, CA 90095-1567
Phone: +1-310-794 5899
Fax: +1-310-206 3051
Email: munnich at atmos.ucla.edu
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