display global data

[Tetsuo Nakazawa]

Dear Jennifer-san,

>>  My friend asked me the following questions, but I could not answer.
>> I hope someone helps me.
>>
>>  Question:
>>   There is a following ctl file. The data is global, starting from
>> -179.75 with 0.5 deg resolution.
>>   When the display command is issued, then GrADS says that the
>> display area is set to like,
>>
>> LON set to 0 360
>> LAT set to ....
>> LEV set to ....
>> Time ..........
>>
>>   The question is that the original ctl shows that the western
>> boundary of the data is from -179.75,
>> however, the display says GrADS changed the longitude, starting from
>> 0. Do you know why?
>>
> When GrADS detects that a grid 'wraps' the globe, it sets the LON
> dimension environment to be 0 to 360. If it doesn't wrap, it sets
> the X dimension environment to be 1 to XSIZE. The test for whether
> a grid wraps goes like this:
> In your descriptor file you have: XDEF n linear v1 v2
> temp =  (v1 + (n*v2) - 360)
> if (fabs(temp-v1) <  0.01) then the grid wraps.
> Non-linear X axes are never tested to see if they wrap.
>

  Thanks.

  Sometimes one would like to plot globally as the data is stored.
And also, one suspects
that the data is wrong or GrADS is wrong if GrADS changes the
starting longitude from 0 deg.

********************************************
Tetsuo Nakazawa
                       nakazawa at mri-jma.go.jp
Typhoon Research Department
Meteorological Research Institute
Tel:  029-853-8671 Fax: 029-853-8735
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