[gradsusr] ctl file for irregular lon and lat dimension

Jeff Duda jeffduda319 at gmail.com
Thu Jun 20 13:19:55 EDT 2019

Keep in mind that it's generally a good idea (but is not strictly required)
that the following relationship is held in the XDEF and YDEF lines:

max_x = min_x + dx*nx
max_y = min_y + dy*ny

What I usually do is find the maximum and minimum latitudes and longitudes
anywhere in the geographic domain and then divide the difference in those
by whatever you set for NX or NY. Use that as the step value. XDEF and YDEF
are largely cosmetic for irregular grids, though. What is most important
for getting your data to show up correctly is having a PDEF entry with the
correct values for whatever your projection is. If your data are not
projected in a way that Grads can support then I'm not sure you can do this
using GrADS.

Jeff Duda

On Thu, Jun 20, 2019 at 1:46 AM wendi harjupa <wendiharjupa at gmail.com>

> Dear GrADS users,
> I need your help with this problem.
> I have two-dimensional data, which have no linear resolution, such below;
> 1. The first, second, third and the last coordinate longitude data are
> 21.2887,  121.29860, 121.30840 and 148.76140, respectively.
> 2. The first, second, third and the last coordinate latitude data are
> 22.70906, 22.70909, 22.70911 and
> 46.19549, respectively.
> I want to make the control file for the data to plot it by grads,
> XDEF LEVEL 2800 121.28870  XXXX
> YDEF LEVEL 2400 22.70906 YYYY
> What number should I use to change XXXX and YYYY?
> and is there special command should I use to handle the irregular spatial
> resolution?
> Very appreciate for your help.
> Thank you very much.
> Best regards,
> wendi
> On Wed, Jun 19, 2019 at 9:17 PM wendi harjupa <wendiharjupa at gmail.com>
> wrote:
>> Dear GrADS user,
>> I want to plot the data which has irregular lon and lat...
>> I donot want to interpolate the data, so I just want to plot it as the
>> original data.
>> My question is how to make the control file for the irregular lon and lat
>> data.
>> I attach two data through this email,
>> 1. asci data which shows the different of lon and lat of the data.
>> 2. Binary format data of the asci data.
>> Thank you very much for your help.
>> best regards
>> wendi
>>  RDCA20150803_0305.bin
>> <https://drive.google.com/file/d/1HDCQXO30JwIRCaxTL-H1pf6eibRvhTpp/view?usp=drive_web>
>>  RDCA20150803_0305.txt
>> <https://drive.google.com/file/d/1l0vSZLO0Z21aBlfuMLF2UJM02m0kXTtC/view?usp=drive_web>
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Jeff Duda, Research Scientist
University of Colorado Boulder
Cooperative Institute for Research in Environmental Sciences
NOAA/OAR/ESRL/Global Systems Division
Boulder, CO
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