Re: [ferret_users] regriding data from (lon lat) axis to (x_page y_page) axis (stereographic projection)

[Cécile Agosta <cecile.agosta@xxxxxxxxx>]

Thank you , it works now !

I didn't have rect_to_curv on ferret5.70 so I downloaded ferret6.1


I had these 3 data file :

    1> ./acan_arthern.nc

 name    
title                            
I        
J        
K         L

 ACC     
Accumulation            
   1:361    
1:61     
...       ...

              
on grid GTH1 with -1.000000E+34 for missing data

             X=-0.5:360.5  Y=-90.2:-59.8


    2> ./lonlat.nc

 name    
title                            
I        
J        
K         L

 LON     
Longitude                       
1:311     1:311    
...       ...

            
degrees on grid GMZ1 with -1.000000E+34 for missing data

             X=-3110:3110  Y=-3110:3110

 LAT     
Latitude                        
1:311     1:311    
...       ...

            
degrees on grid GMZ1 with -1.000000E+34 for missing data

             X=-3110:3110  Y=-3110:3110


    3> ./acanMAR0405.nc

 name    
title                            
I        
J        
K         L

 ACCMAR0405

         
(SNOWHY[D=snowHY.20050101,L=4]-  1:311    
1:311     ...      
1:1

              
on grid GNW1 with -1.000000E+34 for missing data

             X=-3110:3110  Y=-3110:3110

  time range: 01-JAN-2005 18:00


Where LON and LAT are the longitudes and latitudes corresponding to X and Y of ACCMAR0405


I wanted to have the same grid for ACC and ACCMAR0405 to compare them.

Here is the ferret command to do that : 


let lonout=lon[d=2]

let latout=lat[d=2]

let ACC_new=rect_to_curv(ACC[d=1],lonout,latout,1)


Thanks,


Cécile

2008/5/14, Peter Szabo <szabpet83@xxxxxxxxx>:

Dear Cécile,
As i understand you question you need to have your (rectilinear) data set in a curvilinear grid.
You can have it easily by the RECT_TO_CURV function. You only need two curvilinear grid variables (2D fields of lons and lats describing the curvilinear grid) from an other, curvilinear file or from yours:

go mp_stereographic_south
set grid your_old
!now you have variables like `mp_standard_parallel` and `mp_central_meridian` and x_page and y_page

!the `mp_standard_parallel and `mp_central_meridian` are constants (the middle of your map), the x_page and y_page are variables (they are just differences from the standard_parallel and central_meridian). so somehow you need to add them or sub them to get the correct curvilinear coordinates. i did not have time for further analyse.

let x_st=x_page+`mp_standard_parallel`
let y_st=y_page+`mp_central_meridian`

after this you can use:

let your_new=rect_to_curv(your_old,x_st,y_st,1)
save/file="..." your_new

hope this helps a bit,
Peter