Metadata

Metadata information associated with a data model is accessed through its meta member. For example, to access the date that an observation was made:

print(model.meta.observation.start_time)

Metadata values will be validated against the schema when validate is called, when the data model is saved or when a file is read.

>>> from roman_datamodels import datamodels as rdm

>>> model = rdm.ImageModel.create_fake_data()
>>> model.meta.pointing.target_ra = "foo"
>>> model.validate()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/path/to/python/lib/python3.12/site-packages/roman_datamodels/stnode/_node.py", line 251, in __setattr__
    _validate(key, value, schema, self.ctx)
  File "/path/to/python/lib/python3.12/site-packages/roman_datamodels/stnode/_node.py", line 78, in _validate
    return _value_change(attr, tagged_tree, schema, False, will_strict_validate(), ctx)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/path/to/python/lib/python3.12/site-packages/roman_datamodels/stnode/_node.py", line 47, in _value_change
    raise ValidationError(errmsg)
asdf._jsonschema.exceptions.ValidationError: While validating target_ra the following error occurred:
'foo' is not of type 'number'

Failed validating 'type' in schema:
    {'$schema': 'http://stsci.edu/schemas/asdf-schema/0.1.0/asdf-schema',
    'archive_catalog': {'datatype': 'float',
                        'destination': ['WFIExposure.target_ra',
                                        'GuideWindow.target_ra']},
    'description': 'Right ascension in units of degrees at the location '
                    'of\n'
                    'the target aperture.\n',
    'sdf': {'source': {'origin': 'TBD'},
            'special_processing': 'VALUE_REQUIRED'},
    'title': 'Right Ascension of the Target Aperture (deg)',
    'type': 'number'}

On instance:
    'foo'

The set of available metadata elements is defined in a YAML Schema that is installed with roman_datamodels from the RAD (Roman Attribute Dictionary).

There is also a utility method for finding the schema associated with a given model.

>>> raw_science = rdm.ScienceRawModel.create_fake_data()  # Create a model of the desired type
>>> print(raw_science.schema_uri)  # find the associated Schema
asdf://stsci.edu/datamodels/roman/schemas/wfi_science_raw-1.0.0

An alternative method to get and set metadata values is to use a dot-separated name as a dictionary lookup. This is useful for databases, such as CRDS, where the path to the metadata element is most conveniently stored as a string. The following two lines are equivalent

>>> print(raw_science.meta['visit']['start_time'])
2020-01-01T00:00:00.000
>>> print(raw_science.meta.visit.start_time)
2020-01-01T00:00:00.000

In addition the times are stored as Astropy time objects and so the date can be displayed using various formats

>>> print(raw_science.meta.visit.start_time.iso)
2020-01-01 00:00:00.000
>>> print(raw_science.meta.visit.start_time.mjd)
58849.0
>>> print(raw_science.meta.visit.start_time.yday)
2020:001:00:00:00.000