data at 1 point

Matthias Munnich munnich at ATMOS.UCLA.EDU
Fri Feb 11 00:19:17 EST 2005


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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