Architecture

Every scan point generator inherits from the ScanPointGenerator baseclass. This baseclass provides the following API:

class scanpointgenerator.Generator

Base class for all malcolm scan point generators

Variables:

• position_units (dict) – Dict of str position_name -> str position_unit for each scannable dimension. E.g. {“x”: “mm”, “y”: “mm”}
• index_dims (list) – List of the int dimension sizes for the dataset. This will have the same length as the position_units list for square scans but will be shorter for things like spiral scans. E.g. [15]
• index_names (list) – List of the str dimension names for the dataset. This will have the same length as the index_dims. E.g. [“spiral_i”]
• axes (list) – List of scannable names, used in GDA to reconstruct Point in CompoundGenerators

iterator()

An iterator yielding positions at each scan point

Yields:Point – The next scan Point

to_dict()

Abstract method to convert object attributes into a dictionary

classmethod from_dict(d)

Abstract method to create a ScanPointGenerator instance from a serialised dictionary

Parameters:d (dict) – Dictionary of attributes Returns:New ScanPointGenerator instance Return type:Generator

classmethod register_subclass(generator_type)

Register a subclass so from_dict() works

Parameters:generator_type (Generator) – Subclass to register

Each point produced by the iterator represents a scan point, with the following API:

class scanpointgenerator.Point

Contains information about for each scan point

Variables:

• positions (dict) – Dict of str position_name -> float position for each scannable dimension. E.g. {“x”: 0.1, “y”: 2.2}
• lower (dict) – Dict of str position_name -> float lower_bound for each scannable dimension. E.g. {“x”: 0.95, “y”: 2.15}
• upper (dict) – Dict of str position_name -> float upper_bound for each scannable dimension. E.g. {“x”: 1.05, “y”: 2.25}
• indexes (list) – List of int indexes for each dataset dimension, fastest changing last. E.g. [15]
• duration (int) – Int or None for duration of the point exposure

Using the API

You would use a generator in a step scan like this:

>>> for point in generator.iterator():
>>>     for mname, mpos in point.positions():
>>>         motors[mname].move(mpos)
>>>     det.write_data_to_index(point.indexes)