Data Structures

This document details data structures that exist semantically in the framework, but are not structured as classes or dataclasses for reasons of program speed.

These are primarily within numpy.array or ak.Array objects.

Island Window

An island window is a 2-dimensional array of integer values that aims to represent pixellated ionisation activity on a single wire plane. Coordinates correspond to wire, time coordinates. \((x,y) \equiv (\mathrm{time},\mathrm{wire})\). The background of no ionisation activity is represented by a 0 value, while any other positive value represents ionisation.

╭───────────────────────╮
│ 0 | 1 | 0 | 0 | 0 | 0 │
│───────────────────────│
│ 0 | 1 | 1 | 0 | 0 | 0 │
│───────────────────────│
│ 0 | 0 | 1 | 0 | 0 | 0 │
│───────────────────────│
│ 0 | 0 | 1 | 0 | 0 | 0 │
│───────────────────────│
│ 0 | 0 | 1 | 0 | 0 | 0 │
╰───────────────────────╯

The diagram above as an island window would encompass a window spanning x = 5 wires and the entire time axis binned into y = 6 bins.

Construction

Island windows start as a more compact std::vector<std::vector<float>>. The dimensions of the outermost vector represent the number of wires that comprise the relative wire window placed around the reconstructed neutrino vertex position. The inner vector dimensions represent the number of hits on that particular wire. Floats within the innermost vector are the resolved peak hit times of recob::Hits in the neutrino slice.

This initial structure was chosen due to limitations in outputting more complex objects to ROOT TTrees in the LArSoft framework used by the upstream playonverbs/HyperonProduction module.

The functions alg.island._window_to_map and alg.island._window_to_map_numpy both construct a window from the compact format.

Variants

Binary Island Map

The binary island window is an island window with elements that are only either 0 or 1. This represents the simplest level of information stating if a location contains ionisation activity.

• 0 represents a pixel with no activity – or the ‘background’.

• 1 represents any ionisation activity.

Binary island maps are produced by the alg.island._window_to_map and alg.island._window_to_map_numpy functions. The functions that take them as inputs are alg.island._find_map_islands.

Segmented Island Map

The segmented island map is produced after the primary island finding stage and represents ionisation activity separated by their proximity to other connected islands of activity. It has the same shape as a standard island window but instead elements representing activity can be any positive, non-zero integer.

• 0 represents a pixel with no activity – the ‘background’.

• 1..n represents a pixel with activity. Elements with the same number are considered adjacent to one another as per the procedure used by the underlying scipy.ndimage.label.