CS 452/652 Fall 2019 - Lecture 14

Track Measurements

• train control assignments need velocity information
  • preparatory measurements can be taken without full kernel
  • start early before the tracks fill up!
• default turnout setting - use trap loops: small (left/right), medium, large
• middle turnouts: do not set to C/C! (can lead to derailment)

Data Representation

• location, distance
  • millimetre granularity sufficient
  • longest short path (without reverse): ~10.5m
    ⇒ 32-bit integer sufficient
  • keep in mind: size of train, location of pickup!
• time
  • fastest clock: 508 kHz
  • 32 bit can represent > 2 hours ⇒ sufficient
• no floating point!
• if necessary, use fixed-point integer instead
• if necessary, use 64-bit 'long long' integers to hold temporary results during computation

Speed / Velocity

Basics

• speed: train setting 0-14
• velocity: actual travel distance per time
  1. non-linear with speed
  2. different for different trains
  3. different for different parts of track?
  4. changes over time (wear and tear)
• handle at least 1. and 2. by measuring and storing velocity data
  • offline experiments → start now!
  • continuous online measurements?
  • data import/export?

Sensor Measurement

• assume ~70ms continuous sensor polling loop
• unknown (hopefully constant) measurement error
  • train controller box
  • signal latency
  • etc.
• variable measurement error: sensor trigger relative to polling loop → 0-70ms
• processing delays? later... (should be small with dedicated measurement program)

Speed Measurement

• velocity = distance / (stop - start)
• constant error in 'stop' and 'start' cancels out
• maximum variable error: up to 2x 70ms = 140ms
• at speed of 0.5m/sec, this corresponds 7cm
• use averaging (and deviations) or min/max boundaries to deal with uncertainty