background, edm and algorithm description

Introduction

The traccc repository is part of the ACTS project, R&D line for accelerators. It is meant to build up a chain of algorithms that run in track reconstruction.

Sequence description

Connected Component Labelling

The readout of segmented silicon detectors is usually a channel identification and an activation value, this value can be digital or - if analog readout is supported - of some given readout accuracy. In the following, we address pixel detectors and will call the input a cell, it could look something like this:

    /// A cell definition: 
    ///
    /// maximum two channel identifiers
    /// and one activiation value, such as a time stamp
    struct cell {
        channel_id channel0 = 0;
        channel_id channel1 = 0;
        scalar activation = 0.;
        scalar time = 0.;
    };

The first algorithm to be run is to find connected cells per module, also called connected component labelling, for this purpose the SparseCCL algorithm has been implemented following [DOI: 10.1109/DASIP48288.2019.9049184]. It is a two pass algorithm that groups connected cells together into clusters. The following figure from the SparseCCL paper shows four clusters on a module:

Measurement creation

From connected cells, measurements are created, which describe the local measurement and variance information on a measurement module

  /// A measurement definition, fix to two-dimensional here
    struct measurement {
        point2 local = {0., 0.};
        variance2 variance = { 0., 0.};
    };

Spacepoint creation