HoloSpy metadata structure

HoloSpy extends the HyperSpy metadata structure with conventions for metadata specific to its signal types. Refer to the HyperSpy metadata documentation for general metadata fields.

The metadata of any signal objects is stored in the metadata attribute, which has a tree structure. By convention, the node labels are capitalized and the ones for leaves are not capitalized. When a leaf contains a quantity that is not dimensionless, the units can be given in an extra leaf with the same label followed by the _units suffix.

Besides directly accessing the metadata tree structure, e.g. s.metadata.Signal.signal_type, the HyperSpy methods set_item(), has_item() and get_item() can be used to add to, search for and read from items in the metadata tree, respectively.

The holography-specific metadata structure is represented in the following tree diagram. The default units are given in parentheses. Details about the leaves can be found in the following sections of this chapter. Note that not all types of leaves will apply to every type of measurement.

metadata
├── General
│   └── # see HyperSpy
├── Sample
│   └── # see HyperSpy
├── Signal
│   ├── signal_type
│   └── # otherwise see HyperSpy
└── Acquisition_instrument
    └── TEM
        └── Biprism
            ├── azimuth_angle (º)
            ├── position
            └── voltage (V)

General

See HyperSpy-Metadata-General.

Sample

See HyperSpy-Metadata-Sample.

Signal

signal_type

type: string

String that describes the type of signal. Currently, the only HoloSpy specific signal class is hologram.

See HyperSpy-Metadata-Signal for additional fields.

Acquisition Instrument

TEM

Biprism

This node stores parameters of biprism used in off-axis electron holography

azimuth_angle (º)

type: Float

Rotation angle of the biprism in degree

position

type: Str

Position of the biprism in microscope column, e.g. Selected area aperture plane

voltage

type: Float

Voltage of electrostatic biprism in volts

See eXSpy TEM metadata for additional fields.