Re: [ferret_users] Extracting data/value from grided data in rotated Mercator projection

[jagadish karmacharya <j_karmacharya@xxxxxxxxx>]

Hi Ansley,

I have the following grid:

yes? sh data
     currently SET data sets:
    1> ./head_out.nc  (default)
 name     title                                    I            J         K         L
 HT       Terrain Elevation                1:118     1:109     ...       1:1

yes? sh grid ht
    GRID GPK1
 name       axis              # pts     start                     end
 LON       LONGITUDE   118mi    52.372E(52.373)   108.09E(108.09)
 LAT       LATITUDE        109 i     2.378S                 44.79N
 normal    Z
 TIME      TIME                 1 r   01-NOV-1960 00:00    01-NOV-1960 00:00

This is almost similar to 2nd type you mentioned expect for the irregular spacing of points on axis.
Further, I checked the values at few point using the list command; looks like list/x=80/y=20 doesn't give value at 80E, 20N (ie there is some shift).

regards
Jagadish


--- On Mon, 7/6/09, Ansley Manke <Ansley.B.Manke@xxxxxxxx> wrote:

From: Ansley Manke <Ansley.B.Manke@xxxxxxxx>
Subject: Re: [ferret_users] Extracting data/value from grided data in rotated Mercator projection
To: "jagadish karmacharya" <j_karmacharya@xxxxxxxxx>
Cc: "Ferret users" <oar.pmel.ferret_users@xxxxxxxx>
Date: Monday, July 6, 2009, 11:17 AM

Hi Jagadish,
It depends on the way  your grid is listed in the file. Is it coming in on a curvilinear grid?  that is, when you SHOW DATA, are the longitudes and latitudes 2-dimensional variables, similar to this?

yes? show data
     currently SET data sets:
    1> /home/porter/ansley/ans_ferret/curvi/ht_cf.nc  (default)
 name     title                  I         J         K         L
 GEOLON geographic longitude   1:180     1:173     ...       ...
 GEOLAT geographic latitude    1:180     1:173     ...       ...
 VAR     topography            1:180     1:173     ...       ...

If this is the case then you will need to use the SAMPLEXY_CURV function to get the value of the variable at the location in the curvilinear coordinate grid. 



If the variable is a simple variable on a set of coordinate axes defined in longitude and latitude, but irregularly spaced, such as

yes? show data
    2> /home/ansley/data/var.nc  (default)
 name     title                  I         J         K         L
 VAR      topography             1:180     1:90      ...      ...

yes? show grid sst    GRID GCOADS
 name       axis              # pts   start                end
 LON       LONGITUDE          180mr   21E                  19E(379)
 LAT       LATITUDE            90 i   89S                  89N
 normal    Z
 normal    T

Then you can just say

yes? list/x=80/y=20 var

Ansley

jagadish karmacharya wrote:

Hi everyone,

I have grided data in rotated Mercator projection. I can properly plot that data using map projection information. I want to know if I need to extract value at  a location say 80E, 20N
it is enough to load the data and just issue  list/x=80/y=20 var command? Does it take care of the shift we see in the map plot automatically? In other word, the shift we see in map plot is limited to  map plot only or is there similar shift in data reading/extraction. If there is some shift how to extract data  in real world coordinate (at the grid with  80E, 20N in above case)

reagrds
Jagadish