Core Convention
In LARDON, electrons drift along the z-axis (the third spatial axis). All spatial coordinates are expressed in centimetres (cm).Detector Origins
The coordinate origin depends on the detector:ProtoDUNE-II (pdhd, pdvd)
The origin of the (x, y, z) system matches the LArSoft convention. Coordinates are directly compatible with the LArSoft geometry framework.
Other detectors (coldbox, 50L)
The origin is placed at the center of the detector active volume.
ProtoDUNE-II Coordinate System
For both PDHD and PDVD, the axes are aligned with the LArSoft convention. In all cases, the drift direction is along z.In LARDON, z is always the drift coordinate regardless of how the detector is physically oriented. This differs from some other conventions where x or y may be the drift direction.
- PDHD (Horizontal Drift) — the drift direction is horizontal; the anode and cathode planes are vertical.
- PDVD (Vertical Drift) — the drift direction is vertical; the anode (CRP) and cathode planes are horizontal.
View Types
Each wire plane in the TPC is classified as one of two view types:Collection
Unipolar signal. The wire directly collects drifting electrons. Produces a positive-only pulse. Color-coded with a sequential (warm) color map in event displays.
Induction
Bipolar signal. The wire sees an induced charge as the electron cloud drifts past. Produces a positive-then-negative pulse (or negative-then-positive depending on direction). Color-coded with a diverging color map in event displays.
is_collection flag in the hits output table (and the view_type configuration parameter) identifies which type applies to each view.
Channel Ordering
LARDON uses two distinct channel numbering schemes:| Scheme | Description | Typical use |
|---|---|---|
| DAQ channels | Raw hardware channel numbering as assigned by the DAQ electronics. A single module’s DAQ channels can interleave multiple views. | Raw data reading, noise plots per module |
| View channels | Channels numbered within a single view, from 0 to view_nchan[view] - 1. Reflects the physical wire layout. | Event displays, hit positions, reconstruction |
chmap objects and configured in geo.json for each detector. The wire pitch (spacing between adjacent wires) also varies by detector and view and is read from geo.json.
Time and Tick Units
TPC
- The TPC is sampled at a detector-specific rate configured in
geo.json(thesamplingparameter, in MHz). - Time in the reconstruction is expressed in ticks — one tick equals one ADC sample.
- Typical sampling period: ~0.5 µs/tick (2 MHz), but this varies by detector.
- Timestamps in the
eventtable are Unix timestamps (seconds + nanoseconds). - Charge-timing quantities (e.g.
charge_timein theeventtable) are relative to the trigger.
PDS
- The photon detection system has its own sampling rate (
pds_samplingin the configuration, in MHz), which is independent of and typically higher than the TPC sampling rate. - PDS time quantities are stored in microseconds (µs) relative to the trigger.
- Per-channel timing offsets (
chan_time_offset) account for cable or electronics delays between PDS channels.
Output Coordinate System
Reconstructed positions stored in the output HDF5 file use lardon coordinates by default. This is controlled by the"store": {"coord": "lardon"} key in reco_parameters.json:
- z is always the drift coordinate (regardless of physical detector orientation).
- x and y are the two transverse directions, following the LArSoft origin convention for ProtoDUNE-II detectors.
- All distances are in cm.
Summary
| Quantity | Unit / Convention |
|---|---|
| Spatial coordinates | cm |
| Drift axis | z |
| Origin (ProtoDUNE-II) | LArSoft convention |
| Origin (coldbox, 50L) | Center of active volume |
| TPC time | ticks (detector-dependent µs/tick) |
| PDS time | µs relative to trigger |
| Default output frame | lardon coordinates |