Global Metadata File Structure

Global Metadata File Structure#

When converting model data to netCDF or HDF5, it is essential to provide detailed model metadata. In this guide, we will explore how to construct metadata using parameter files. These parameter files follow specific rules and conventions, ensuring consistency and compliance with the CF Metadata Conventions.

Overview#

Parameter files define various model parameters used to construct metadata. All parameters must adhere to the CF Metadata Conventions, which can be found here.

General Rules#

  1. Comments and Blank Lines:

    • Lines starting with # are comments and are ignored.

    • Blank lines are ignored.

    • Leading and trailing blank spaces are ignored.

  2. Parameter Definitions:

    • Each parameter should be defined on a new line using the key=value format.

    • Quotes are not required for the values and should not be included.

  3. Grouping and Sub-grouping:

    • Lines starting with - indicate a new parameter definition.

    • Lines starting with > indicate a new parameter group.

    • Each parameter group should contain one or more parameter definitions.

    • Lines starting with >> indicate a new parameter sub-group. Each parameter group (>) may contain as many subgroups (>>) as necessary.

    • Each parameter sub-group should be nested under a parameter group.

    • Each parameter sub-group should contain one or more parameter definitions.

Metadata#

There are two types of model metadata. The global metadata that apply to the entire model, and variable metadata that are defined for individual variables (coordinate and data variables). To manage this grouping effectively, we place these metadata into two separate global and variable metadata files. This guide describes the global metadata structure.

Global Metadata#

The global metadata apply to the entire model. You will find a template file for the global metadata under the template directory (template/global_metadata_template.txt). The global metadata includes:

Delimiters#

Define the delimiters that are used to separate data columns in both input and output files. The value assigned to data represents the characters that separates columns in your data file. If your file is space-delimited, leave the data value blank. The geocsv represents the delimiter to use to separate the GeoCSV data columns.

> delimiter
    data =
    geocsv = |

HDF5 Groups#

These attributes applies to the HDF5 files only and will be ignored by netCDF. By default, the model values and other 3D data are stored as uniform grids within the volumes group. The elevation of surfaces or other 2D data are stored within the surfaces group.

> groups
     volumes = volumes
     surfaces = surfaces

netCDF Output Format#

Specify the netCDF format to use, as defined in prop/shared_prop.py.

- netcdf_format = NETCDF4C

Model Information#

Provide details about the model, including its name, title, summary, and references.

> model
    model = Cascadia_ANT+RF_Delph2018
    title = 3D vertical shear-wave velocity model of the Cascadian forearc from the joint inversion of ambient noise dispersion and receiver functions
    summary = Cascadia_ANT+RF_Delph2018 was created from the joint inversion of ambient noise Rayleigh waves dispersion measurements (8-50 seconds) and adaptive CCP-derived receiver functions (see Delph et al., 2015, 2017 for details of methodology; Delph et al., 2018 for details of this model).
    reference = Delph, Levander, and Niu (2018)
    reference_pid = doi:10.1029/2018gl079518
    data_revision = r0.1
    version = v0.0

Repository Information#

Include the persistent identifier for the model in the repository. This parameter is option set to blank if not available.

> repository
    repository_pid = doi:10.17611/dp/cascadiaantrfd2018

Corresponding Author#

Provide details about the corresponding author.

> corresponding_author
    author_name = Jonathan R. Delph
    author_email = jdelph@purdue.edu
    author_institution = Purdue University
    author_url = https://www.eaps.purdue.edu/delph/

Geospatial Limits#

Define the geographical area covered by the dataset.

> geospatial
    geospatial_lon_min = -124.8
    geospatial_lon_max = -120
    geospatial_lon_units = degrees_east
    geospatial_lon_resolution = 0.2
    geospatial_lat_min = 40
    geospatial_lat_max = 49
    geospatial_lat_units = degrees_north
    geospatial_lat_resolution = 1
    geospatial_vertical_min = -3
    geospatial_vertical_max = 80
    geospatial_vertical_units = km
    geospatial_vertical_positive = down

Global Attributes#

Include additional parameters as global attributes.

> global_attrs
    keywords = seismic, Rayleigh waves dispersion, shear wave, s wave, Cascadian forearc, ambient noise dispersion, receiver functions
    acknowledgment = Model was provided by Jonathan R. Delph of Department of Earth, Environmental and Planetary Sciences, Rice University
    history = [2024-01-03] Converted to netCDF via CRESCENT data tools.
    comments = CRESCENT CVM tools development project.
    data_layout = vertex
data_layout attribute#

Each model should also include a global attribute data_layout. This attribute specifies the layout of the data in the file and can take two possible values:

  • 'vertex' for vertex-based layout (values are specified at vertices)

  • 'cell' for cell-based layout (values are specified at the centers of grid cells)

Currently, the CVM-Tools support vertex-based values.

Grid Mapping#

Specify a recognized grid mapping name. Must correspond to a recognized grid mapping name, (more information)

Currently supporting:

  • latitude_longitude – This grid mapping defines the canonical 2D geographical coordinate system based upon latitude and longitude coordinates.

  • mercator – Mercator

- grid_mapping_name = latitude_longitude

Universal Transverse Mercator (UTM) Zone#

Define the UTM zone and ellipsoid reference.

- utm_zone = 10
- ellipsoid = WGS84
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