[111] Regridding corners question

From: Robert Oehmke <robert.oehmke_at_nyahnyahspammersnyahnyah>
Date: Wed Aug 14 2013 - 16:41:23 MDT

Hi Katie,

 This is Bob Oehmke from ESMF. If this is indeed ESMF conservative regridding then the corners of each grid cell describe the area over which the quantity in that cell is represented. The integral that the conservative regridding is preserving is the sum of the quantity in each cell multiplied by its area. As you change the corners you change the area. This changes how the source and destination grids overlap as well as the total integrated value.

Since the corners define the cells over which your data is described you want the corners to be positioned to best represent that area according to what you know about the data.

Let me know if the above makes sense. I know it's not as helpful as saying use "X digits of rounding", but where you put your corners says a lot about your data so its hard for me to say anything specific without knowing a lot about your case.

Where is the rounding happening?


- Bob

On Aug 14, 2013, at 12:23 PM, Mary Haley wrote:

> Hi Katie,
> Are you talking about ESMF regridding? And if so, are you using the "conserve" method?
> I don't know if there are any best practices, as it probably depends on the spacing of your grid, and the physics behind the points you are regridding.
> I'm hoping the ESMF folks have some good suggestions. I've CC'ed them.
> --Mary
> On Aug 12, 2013, at 5:11 PM, Travis, Katherine wrote:
>> Hi,
>> I am regridding a 12km by 12km lambert conical conformal grid of sparse emissions over the U.S. To a 1/2 by 2/3 degree grid over the same domain. If a choose the grid corners to be rounded to zero decimal places, I get a slightly different answer in my final emissions than if I round the grid corner to 2 decimal places which is actually slightly (1%) less than the original emissions. Why would this occur, and what is 'best practices' in choosing the grid corners for this scenario?
>> Thank you,
>> ~Katie
>> --
>> Katherine R. Travis
>> PhD Candidate
>> Harvard University
>> ktravis@fas.harvard.edu
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Received on Wed Aug 14 16:42:20 2013

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