Author: Paul Ullrich Email: [email protected]

TempestRemap is a conservative, consistent and monotone remapping package for arbitrary grid geometry with support for finite volumes and finite elements. There is still quite a bit of work to be done, but any feedback is appreciated on the software in its current form.

If you choose to use this software in your work, please cite our papers:

Paul A. Ullrich and Mark A. Taylor, 2015: Arbitrary-Order Conservative and Consistent Remapping and a Theory of Linear Maps: Part 1. Mon. Wea. Rev., 143, 2419–2440, doi: 10.1175/MWR-D-14-00343.1

Paul A. Ullrich, Darshi Devendran and Hans Johansen, 2016: Arbitrary-Order Conservative and Consistent Remapping and a Theory of Linear Maps, Part 2. Mon. Weather Rev., 144, 1529-1549, doi: 10.1175/MWR-D-15-0301.1.

Prebuilt binary packages for x64 Linux and MacOS are provided through conda-forge for conda projects and as a Julia JLL package.

For Conda:

 > conda install -c conda-forge tempest-remap 
 > GenerateCSMesh --res 6 --file cubedsphere_6.netcdf --out_format NetCDF4
 Parameters:
   --res <integer> [6] 
   --file <string> ["cubedsphere_6.netcdf"] 
   --out_format <string> ["Netcdf4"] 
   --alt <bool> [false] 
 =========================================================
 ..Generating mesh with resolution [6]
 ..Writing mesh to file [cubedsphere_6.netcdf] 
 Nodes per element
 ..Block 1 (4 nodes): 216
 ..Mesh generator exited successfully
 =========================================================

For Julia (v1.7+):

julia> using Pkg; Pkg.add("TempestRemap_jll")
julia> using TempestRemap_jll

julia> run(`$(TempestRemap_jll.GenerateCSMesh_exe()) --res 6 --file cubedsphere_6.netcdf  --out_format Netcdf4`);
Parameters:
  --res <integer> [6] 
  --file <string> ["cubedsphere_6.netcdf"] 
  --out_format <string> ["Netcdf4"] 
  --alt <bool> [false] 
=========================================================
..Generating mesh with resolution [6]
..Writing mesh to file [cubedsphere_6.netcdf] 
Nodes per element
..Block 1 (4 nodes): 216
..Mesh generator exited successfully
=========================================================

TempestRemap now supports a robust autotools-based configuration/build system. Building with the standard autotools toolchain simplifies the process of linking for downstream packages like MOAB, and in conda feedstock. The builds produce both linkable TempestRemap libraries and several specialized tools (or drivers) that can be installed in user-specified installation directories.

Please follow the build instructions below:

1. cd $TEMPESTREMAP_SRCDIR && autoreconf -fi
2. mkdir -p build && cd build
3. Configure TempestRemap:

   ../configure --prefix=$INSTALL_DIR \ # Install dir for TempestRemap libraries
                --with-blas=$BLAS_LIB \ # Path to BLAS libraries
                --with-lapack=$LAPACK_LIB \ # Path to LAPACK libraries
                --with-netcdf=$NETCDF_DIR \ # With NetCDF-C interfaces
                --with-hdf5=$HDF5_DIR # If NetCDF was build with HDF5

5. Build TempestRemap: make all
6. Install TempestRemap: make install

Additionally, users can provide the appropriate compilers with the environmental flags (CC, CXX, FC, F77, etc.) and control the compilation/link flags (CXXFLAGS, CPPFLAGS, LDFLAGS, LIBS) as necessary.

The software can be obtained from the GITHub repository via git:

git clone https://github.com/paullric/tempestgecore.git

You will likely need to edit the first couple lines of the Makefile to customize the NetCDF paths and change any compiler flags. Once you have modified the Makefile, build the code:

make -f Makefile.gmake all

To clean out the object file and return the sources to pristine condition, you can execute the following:

make -f Makefile.gmake clean

The remapping process requires multiple stages. First you will need an Exodus file (file extension .g) for your input mesh and your output mesh. This can either be done via the SQuadGen mesh utility, or via the three GenerateMesh executables that come with TempestRemap.

For a cubed-sphere mesh:

./GenerateCSMesh --res <Resolution> --alt --file <Output mesh filename>.g

For a latitude-longitude mesh:

./GenerateRLLMesh --lon <longitudes> --lat <latitudes> --file <Output mesh filename>.g

For a geodesic mesh:

./GenerateICOMesh --res <Resolution> --dual --file <Output mesh filename>.g

Once your input and output meshes are generated, you will need to generate the overlap mesh (that is, the mesh obtained by placing the input and output mesh overtop one another and recalculating intersections). This can be done as follows:

./GenerateOverlapMesh --a <Input mesh>.g --b <Output mesh>.g --out <Overlap mesh>.g

Once the overlap mesh is generated, you can now generate the weight file, which the contains information on remapping from one mesh to the other. The type of offline map desired is specified by --in_type and --out_type, which can be one of the following:

fv - Finite volume mesh, with degrees of freedom stored as volume averages cgll - Continuous finite element method (such as spectral element) dgll - Discontinuous finite element method (such as discontinuous Galerkin)

Offline map generation is then performed as follows:

For finite volume to finite volume remapping:

./GenerateOfflineMap --in_mesh <Input mesh>.g --out_mesh <Output mesh>.g \
                     --ov_mesh <Overlap mesh>.g --in_np <Remapping Order> \
                     --out_map <Output map>.nc

Monotone remapping in this case can be achieved with --in_np 1.

For finite element to finite volume remapping:

./GenerateOfflineMap --in_mesh <Input mesh>.g --out_mesh <Output mesh>.g \
                     --ov_mesh <Overlap mesh>.g --in_type [cgll|dgll] \
                     --out_type fv --in_np <Input order> --out_map <Output map>.nc

Monotone remapping in this case can be achieved with argument --mono.

For finite volume to finite element remapping:

./GenerateOfflineMap --in_mesh <Input mesh>.g --out_mesh <Output mesh>.g \
                     --ov_mesh <Overlap mesh>.g --in_type fv --out_type [cgll|dgll] \
                     --in_np <Input order> --out_np <Output order> --out_map <Output map>.nc

Monotone remapping in this case requires --mono and --in_np 1.

For finite element to finite element remapping:

./GenerateOfflineMap --in_mesh <Input mesh>.g --out_mesh <Output mesh>.g \
                     --ov_mesh <Overlap mesh>.g --in_type [cgll|dgll] \
                     --out_type [cgll|dgll] --in_np <Input order> \
                     --out_np <Output order> --out_map <Output map>.nc

Monotone remapping in this case requires --in_np 1 and --out_np 1.

In each case, the linear weights file will then be written to <Output map>.nc in SCRIP format (although it’s a bare-bones version of SCRIP format at the moment and I’m not sure it’ll work with SCRIP utilities). Now that the map is generated you can apply it to your data files:

The offline map can be applied using the ApplyOfflineMap utility:

./ApplyOfflineMap --map <Output map>.nc --var <Comma-separated list of variables> \
                  --in_data <Input data>.nc --out_data <Output data>.nc

The remapped fields should then appear in <Output data>.nc. Note that if your output mesh is rectilinear, such as a latitude-longitude mesh, the data will automatically be arranged with horizontal spatial dimensions lat and lon.

Please let me know if you have any problems / bugs / comments / feature requests.