[ncl-talk] Triangular mesh interpolation routine

[Dennis Shea]

The following suggests an approach to achieve your objective.

A user wanted to interpolate curvilinear (NARR) data to specific locations.
The user also needed to vertically interpolate to specific pressure levels
prior to interpolating to the locations.

Look at: http://www.ncl.ucar.edu/Applications/narr.shtml
Example 7

Several steps were used:

 [1] A previously generated ESMF weight file was used to regrid
(interpolate) the NARR curvilinear grid to a high resolution rectilinear
grid.

 [2] The linint2_points function then used the generated rectilinear grid
as the input to linint2_points_Wrap

===
There are several ESMF examples the interpolate 'spectral element'
(triangular mesh) to rectilinear grids.
ESMF 10, 11, 17-19

[1] Using one of the examples as a base, generate a weight file (say):
     Opt at WgtFileName="Trimesh_to_RecLin.nc"

[2]
Based upon the function  'narr_to_points' in the above Example 7, you
should create a (say) 'trimesh_to_points' function. If not appropriate,
delete the vertical interpolation portion of the function. This function
could be reused for other interpolations.


Good luck


On Fri, Mar 24, 2017 at 9:10 AM, Mary Haley <haley at ucar.edu> wrote:

> Dan,
>
> You might want to check out the ESMF regridding examples page:
>
> http://www.ncl.ucar.edu/Applications/ESMF.shtml
>
> Example #14 regrids a triangular mesh to a 5 degree grid:
>
> http://www.ncl.ucar.edu/Applications/ESMF.shtml#ex14
>
> There are also a couple of examples associated with the NCL User Guide:
>
> http://www.ncl.ucar.edu/Applications/NUG.shtml
>
> Search for "triangular". You can actually download the data files for
> these examples and run them yourselves.  The data file link is at the top
> of the page.
>
> --Mary
>
>
> On Wed, Mar 22, 2017 at 1:41 AM, Yu, Hao-Cheng <danishyo at gmail.com> wrote:
>
>> Hi everyone
>>
>> From website, I know there're lot of routines to do triangular plot and
>> regriding.
>> Since plot can be made by predefined FE mesh by specified sfYArray,
>> sfXArray & sfElementNodes.
>> I will assume there must be some interpolation routine for FE mesh, but I
>> can't find this on website.
>>
>> Is there any 2D interpolation routine we can use directly by specifying
>> above 3 vars with desired output XY points?
>> For example, assume this routine called "tri_interp".
>> Pre-defined FE mesh var are X,Y,ele, field to interpolate is ZZ, output
>> points are outX, outY.
>> Then we can get output points value by out_interp=tri_interp(X,Y,ele,
>> ZZ,outX,outY)
>>
>> For regular grid, like linint2_points can provide similar function and
>> efficient.
>> Just wonder, is there any similar function for uninstructed grid except
>> Natgrid package (which will be quite time consuming if FE mesh is large)?
>>
>> Dan
>>
>>
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