Page Comparison

...

1. Lat/Lon → SE 
   
   1. FV→SE "mono".   Disabling the conservation constraint with --noconserve does not improve accuracy
   2. FV→SE "highorder" is accurate, but care must be taken with negative weights.  . 
   3. NOTE:  For Lat/Lon grids, check the min/max of the weights - if the values are far outside the "[0,1]" interval, may need more coefficients for Vandermonde inverse near poles: edit LinearRemapFV.cpp: nRequiredFaceSetSize = 2*nCoefficients. 

Testing

Important issues to test:

...

NCO as of 4.9.0-beta01 can test maps for conservation and consistency.   See:  Assess and Address Regridding Weights in Map-Files with ncks.  

In addition, maps can be checked for accuracy.   TempestRemap can automatically generate some standard test functions which can then be remapped and we can compute the mapping error, and check if it is at the expected level. 

...

NEW AS OF NCO 4.9.0-beta01 and TR as of 2019/11:   In practice, all 1st order conservative maps give the same l2 and max error if they pass the conservation and consistency checks.  For higher order maps, these errors can be used to compare different algorithms.  

Check the quality of the mapping file with "ncks --chk_map map.nc"

1. sum of area weights is close to physical area 

2. mapping weights are between 0 and 1.  for higher order maps, it may be acceptable for small overshoots, but we need to test this. 

3. Consistency:  Row sum of weights = 1.

   1. Should be 1 to machine precision for all grids where a >= b.  (global → regional)
   2. For grids with a<b (such as ocn→atm) row sums should be 1.0 at all ocean points, 0 at all land points, and between 0 and 1 at coastal points.   
4. Conservation:  area_b weighted column sum of weights =  area_a (exact for conservation, close otherwise)  
   1. Should be equal to machine precision for all grids where a <= b. (regional → global)
   2. For grids with a>b (such as atm->ocn) should be equal to machine precision at all ocean points, 0 at all land points and between 0 and 1 at coastal points
   3. Non-conservatives maps are expected to have small errors.    The traditional ESMF bilinear map does not include areas in the map file and this metric might not be accurate.  
5. no missing target points (unless source grid has holes)

...