Supported Grid Formats#

Overview#

UXarray is written around the UGRID conventions, which is a standard for storing unstructured grid model data in the NetCDF file format. As of the most recent release, the following grid formats are supported:

  • UGRID

  • MPAS

  • SCRIP

  • EXODUS

  • ESMF

While each of these formats can be encoded in the UGRID conventions, the amount of information that is parsed from them varies. The following sections describes how each format is converted into the UGRID conventions and what variables are directly parsed.

UGRID#

The UGRID conventions are a standard for for storing unstructured grid (a.k.a. unstructured mesh, flexible mesh) model data in a Unidata Network Common Data Form (NetCDF) file.

These conventions are focussed on representing data for environmental applications, hence the motivation for starting from the Climate & Forecasting (CF) Metadata Conventions, The CF Conventions have been the standard in climate rx`earch for many years, and are being adopted by others as the metadata standard (e.g. NASA, Open Geospatial Consortium). The CF conventions allow you to provide the geospatial and temporal coordinates for scientific data, but currently assumes that the horizontal topology may be inferred from the i,j indices of structured grids. The UGRID Conventions outline how to specify the topology of unstructured grids.

The standard was developed over a period of several years through the UGRID Google Group which had members from many different unstructured grid modeling communities (including SELFE, ELCIRC, FVCOM, ADCIRC). From these discussions Bert Jagers (Deltares) created the first draft of this document, and the community worked to develop version 1.0.

References#

MPAS#

The Model for Prediction Across Scales (MPAS) is a collaborative project for developing atmosphere, ocean and other earth-system simulation components for use in climate, regional climate and weather studies.

The defining features of MPAS are the unstructured Voronoi meshes and C-grid discretization used as the basis for many of the model components. The unstructured Voronoi meshes, formally Spherical Centriodal Voronoi Tesselations (SCVTs), allow for both quasi-uniform discretization of the sphere and local refinement. The C-grid discretization, where the normal component of velocity on cell edges is prognosed, is especially well-suited for higher-resolution, mesoscale atmosphere and ocean simulations. The land ice model takes advantage of the SCVT-dual mesh, which is a triangular Delaunay tessellation appropriate for use with Finite-Element-based discretizations.

References#

SCRIP#

The Spherical Coordinate Remapping and Interpolation Package (SCRIP) package is a software package used to generate interpolation weights for remapping fields from one grid to another in spherical geometry.

A SCRIP format grid file is a NetCDF file for describing unstructured grids.

References#

EXODUS#

EXODUS is a binary format based on NetCDF, leading to smaller file sizes compared to ASCII formats. It is system independent and typically consists of nodes (geometric points), elements (e.g., triangles, tetrahedrons), material properties, boundary conditions, and results from analysis.

Moreover, EXODUS facilitates efficient data storage and retrieval for computational simulations, aiding in the management and analysis of complex engineering and scientific datasets. It supports a wide range of finite element analysis applications and provides interoperability with various simulation software packages. Additionally, the format ensures compatibility across different platforms, enhancing collaboration and data exchange within the scientific community.

References#

ESMF#

The Earth System Modeling Framework (ESMF) is high-performance, flexible software infrastructure for building and coupling weather, climate, and related Earth science applications. The ESMF defines an architecture for composing complex, coupled modeling systems and includes data structures and utilities for developing individual models.

ESMF supports a custom unstructured grid file format for describing meshes, which is more compatible than the SCRIP format.

References#

Parsed Variables#

Each unstructured grid formats varies in the amount of information contained about the grid. UXarray parses the variables represented in each format and represents them in the UGRID conventions.

Note

Even though each unstructured grid format has a varying number of support variables, UXarray provides support for constructing additional variables, which is discussed in the next sections.

Coordinates#

UGRID MPAS SCRIP EXODUS ESMF
node_latlon Yes Yes Yes No Yes
edge_latlon Yes Yes No No No
face_latlon Yes Yes Yes No Yes
node_xyz Yes Yes No Yes No
edge_xyz Yes Yes No Yes No
face_xyz Yes Yes No Yes No

Connectivity#

UGRID MPAS SCRIP EXODUS ESMF
face_node Yes Yes Yes Yes Yes
face_edge Yes Yes No No No
face_face Yes No No No No
edge_node Yes Yes No No No
edge_edge No No No No No
edge_face Yes Yes No No No
node_node Yes No No No No
node_edge Yes No No No No
node_face Yes Yes No No No