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Re: [ferret_users] any existing algorithms to convert from rectangularto square grids?



Hi Janeen,
Welcome to the Ferret community!  

The topic you want to read up on in the Users Guide is "regridding".  You read in the data on whatever input grid it's on, and then define the output grid you wish to use, and define a new variable which is the variable regridded to the new grid.

For example, say that the file mydata.nc  has a variable called temp. Define new axes, x2deg, y2deg (or any axis names you choose) and then define the new variable and save it to a new netcdf file.
yes? use mydata.nc

yes? define axis/x=0:358:2/modulo/units=degrees_east x2deg
yes? define axis/y=-90:90:2/units=degrees_north y2deg

yes? let new_temp = temp[gx=x2deg,gy=y2deg]

yes? save/file=newfile.nc new_temp
The default regridding operation is a linear interpolation to put data onto the new grid.  There are also options to use averaging, and several other methods which are outlined in the Users Guide.

Ansley


Janeen wrote:
Hello All,

Sorry if this is a duplicate. I sent this in, inadvertently before I had subscribed.   But the e-mail did not bounce so I don't know if this has been posted or not.

I'm a mostly inexperienced ferret user.  I have a task in which I must convert a netCdf .nc files, which contains rectangular lat/long grids cells to square grid cells.  The rectangular cells are sometimes regular sometimes variably sized.   I think ferret may be able to accomplish this.   If I read the file into ferret, with the rectangular spacing, can I then just print it back out, specifying the square spacing between the points.  Is this something that ferret can handle?  Or must I specify some sort of transformation function in order to get the correct values for the data at the new points I want to print out. 
If anyone has done this before and would be willing to share their experience that would be great.

Cheers!

Janeen

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Ansley Manke, NOAA/PMEL   ansley.b.manke@noaa.gov
7600 Sand Point Way NE, Seattle WA
Phone 206-526-6246,  FAX 206-526-6744


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