[gradsusr] fwrite gridding issue

[Thomas Robinson]

Aloha Eric,

Thank you for your input.  The issue I seem to be having is with meridional
wrap around also.  Does GrADS have the same behavior for the y coordinate
and will something similar (ie 'set y 1 YSIZE') work as well?  Should I not
use set lat and set lon, but use 'set y 1 YSIZE' and 'set x 1 XSIZE'
instead when I do my fwrite?

This takes about four and a half days to run, so if I have to rerun it I
want to make sure I have everything set correctly.

-Tom

On Wed, May 9, 2012 at 6:58 PM, Eric Altshuler <ela at cola.iges.org> wrote:

> Tom,
>
> There are several possible causes for the problem you're describing, but I
> suspect it is due to the wraparound behavior in grads when you have global
> data and your longitude range is 0-360 (or -180 to 180, etc.) In this
> situation, if the number of longitudes in your dataset is XSIZE, fwrite
> will write XSIZE+1 columns (longitudes) of data to the output file, with
> the last column being a duplicate of the first one (X=1). To get around
> this behavior, replace your 'set lon 0 360' command with the following:
>
> 'set x 1 XSIZE'
>
> where XSIZE is the number of longitudes specified in the xdef line of your
> ctl file. Now, fwrite will write XSIZE columns of data instead of XSIZE+1.
>
> If this change doesn't fix your problem, there may be a bug in your
> fortran code. Also, if your fortran code writes the output file using
> sequential access, your ctl file for the output data needs to include
> 'options sequential'.
>
> Best regards,
>
> Eric L. Altshuler
> Assistant Research Scientist
> Center for Ocean-Land-Atmosphere Studies
> 4041 Powder Mill Road, Suite 302
> Calverton, MD 20705-3106
> USA
>
> E-mail: ela at cola.iges.org
> Phone: (301) 902-1257
> Fax: (301) 595-9793
>
> ----- Original Message -----
> From: "Thomas Robinson" <ter at hawaii.edu>
> To: "GrADS Users Forum" <gradsusr at gradsusr.org>
> Sent: Wednesday, May 9, 2012 11:35:59 PM
> Subject: [gradsusr] fwrite gridding issue
>
>
> Aloha,
>
> I used fwrite to write out to a binary file in order to create a large
> file with about 48000 time steps for global data (because I am crazy). I
> noticed that when I use fortran to create a new data file that has all
> 48000, it doesn't match with what the original data plotted, instead it
> seems skewed. No manipulations were done to the data, it was just read it
> all in and write it out. When I tried to loop the data, I further noticed
> that the northern border looped around the south and then moved upwards
> back to the north. It just keeps looping around and it's odd because the
> top boundary of the map isn't continuous with the bottom boundary (unlike
> the side boundaries which are continuous). Anyways, I am wondering why this
> happened and what I can do to make it work out correctly.
>
> Here is my fwrite code. it is the first time step, nt is the last time
> step, chi is the velocity potential that was calculated using 'define chi =
> fish_chi(UGRDprs,VGRDprs)' :
> *# set up global domain
> 'set lev 200 '
> 'set lat -90 90'
> 'set lon 0 360'
> *#**************************************************************
> say 'write data out to binary file called CHI.200hPa'filenum'.dat'
> 'set fwrite -le -sq -cl CHI_200hPa_'filenum'.dat'
> 'set gxout fwrite'
> while (it <= nt)
> 'set t 'it
> 'display chi'
> it=it+1
> endwhile
> 'disable fwrite'
>
> Mahalo for your help!
> -Tom
>
> --
> Tom Robinson
> President Graduate Student Organization
> Student Caucus Representative for the Graduate Student Organization
> Graduate Student - Department of Meteorology
> 732-718-2323
>
>
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-- 
Tom Robinson
President Graduate Student Organization
Student Caucus Representative for the Graduate Student Organization
Graduate Student - Department of Meteorology
732-718-2323
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