Distance Estimation

1
Distance Estimation
Lei Yao leiyao_at_aol.com

• Fakultät für Elektrotechnik und
  Informationstechnik
• Lehrstuhl für Kommunikationstechnik
• Prof. Dr.-Ing. Rüdiger Kays

2
Distance Estimation

• outline
• 1 Introduction
• 2 Stereo-Cameras
• 3 Radar Sensors
• 4 Laser Scanners
• Laser waves
• In principle time of flight
• In principle triangulation
• 5 Ultrasonic Systems
• 6 Summary

Lei Yao
3
Distance Estimation
1. Introduction

• systems for distance estimation
• active systems
• Emission of controlled energy from a source and
• consequent detection of reflected energy
• Laser, Ultrasound, Radar
• passive systems
• Stereovision

• Algorithms for telemetry
• triangulation
• Stereo Cameras, Laser
• time-of-flight range finders
• Laser, Ultrasound, Radar

?
Lei Yao
4
Distance Estimation

• 2. Stereo-Cameras

Block diagram of the process
Com- parison with vehicle model
Distance estimation
Feature extraction
Relevant objects
Cluster
Image area raised objects
Image segment
1
Vehicle recognition
Lei Yao
5
Distance Estimation
P
Principle for distance estimation
Disparity ?u u0 u1
Distance d f b ?u
d
f
u1
u0
1
b
Lei Yao
6
Distance Estimation

• determine correspondent features

Lei Yao
7
Distance Estimation

• The other raised objects (guide posts, bushes
  and so on) can also be detected as object
  hypothesis

Compare the relative speed distinguish standstill
objects and moved objects
Kalman tracking filter local card
Lei Yao
8

• Example The camera captures and detects lane
  markings on the road

16
Distance Estimation
Lei Yao
9
Distance Estimation

• 3. Radar Sensors

RADAR Radio Detection And Ranging Radar is a
remote sensor that emits microwave in
order to measure reflections for detection
purposes
Microwave wavelength about 1 mm to 1 m
Radar sensors for vehicles use millimeter waveband
Transmitter Receiver Antenna Electronics
system
Lei Yao
10
Distance Estimation

• Transmit microwave pulses towards a target
• Receive a return portion of the transmitted
  signal
• Observe the time delay of the returned signals

17
Lei Yao
11
Distance Estimation
Some radar sensors determine relative speed too

• Frequency 76.5 GHz
• Max. Range 120 m
• Range Resolution 1m
• (Beam angle 3º )

16
Lei Yao
12
Distance Estimation
4. Laser Scanners
4.1 Laser waves

• LASER Light Amplification by Stimulated
  Emissions of Radiation
• LADAR Laser Detection And Ranging
• LIDAR Light Detection And Ranging

Laser scanners use laser light instead of
microwaves to sense a target
Lei Yao
13
Distance Estimation

• Atoms absorb and give up energy
• Absorb energy higher level of energy
• Emit light return to a lower energy level

First working laser using ruby rod pumped by a
flash lamp
semiconductor diode aluminum gallium arsenide
(AlGaAs) diodes wavelength 850 nm
Lei Yao
14
Distance Estimation
4.2 In principle time of flight
Laser travels at the speed of light
Distance pulse travels speed of light
time Range 0.5 speed of light time
Tens to hundreds of pulses per second

• Phase-shift
• Laser is modulated by means of a sine wave.
• The phase shift between send and receive is
  proportional to the time of flight

Lei Yao
15
Distance Estimation
exploration of a scene mirrors
Transmitter
Modulated laser light
Transmitted beam
Reference phase
Laser beam
Received light
Scanning mirror unit
Receiver photomultiplier phase detector
5
Lei Yao
16
Distance Estimation
Apertures Optical focusing devices (lenses,
mirrors)

• Range 0.2 ... 30 m.
  100 m are possible
• Accuracy 5 mm
• Measuring rate Typically 5 Hz (up
  to 10 Hz available)
• Interface RS 232 / RS
  422
• Analogue output 4 ... 20 mA

14
14
Lei Yao
17
Distance Estimation

• 4.3 In principle triangulation

a, b, C gt B
camera
a
C
B
(baseline)
c
b
A
point project
Lei Yao
18
Distance Estimation
Laser point scanner Simplicity
Light plane, Grid and so on

• Range SB 250 mm
• Range SA 225 mm
• Max. deviation 0.7 mm
• Interface RS232(option
  RS 485)
• Output 0 10 DCV
  or 4 20 mA

Sensor
15
SA
Camera
SB
Laser
Lei Yao
19
Distance Estimation
5. Ultrasonic Systems

• Ultrasounds Mechanic vibrations and waves

Frequencies 16 kHz -- 1000 MHz
Create Ultrasound Piezoelectric Effect Signal
mechanical deformation vibration
ultrasonic waves
Impulses or sine waves
343m/s at atmosphere
Time-of-Flight Range Finders
Lei Yao
20
Distance Estimation
Emitter
A
Osc.
Receiver
B
Detector
Object
A
t kHz
B
Threshold
t
t0
Lei Yao
21
Distance Estimation
little energy is reflected towards the receiver

• Output analogue
  switching
• Sensing distance 100 ---- 8000 mm
• Resolution lt 2 mm
• Switching frequency 5 --- 125 Hz
• Beam angle 8?
• Analogue output 0 --- 10 V / 4 ---
  20 mA
• Interface
  RS 232 / RS 485

15
Lei Yao
22
Distance Estimation
6. Summary

• Challenge detect vehicles in great distance
• order them in different lanes

Lei Yao
23
Distance Estimation

• Radar systems do not offer sufficient lateral
  resolution for lane determination

Laser and Infrared systems Resolution and
Range
problems
Ultrasound only usable for near field
Stereo camera systems Most suitable for these
tasks
Expensive equipment
Lei Yao