Introduction
LIDAR is an acronym for Light Detection and ranging. LIDAR systems are used in many industries and come in a variety of forms. The fundamental part of any LIDAR system is a one dimensional distance or range measurement device. This fundamental task of distance measurement is accomplished in a variety ways including interferometry, time of flight, and geometrical measurement. These different systems use different types of waves including optical light, laser light, infrared light, or others.
Systems are commonly implemented in one, two, or three dimensional setups. Two and three dimensional systems generally use one dimensional ranging technology and a moving mirror to sweep the distance measurement in one or two directions.
LADAR/LIDAR systems are used frequently in many robotics systems. One and two dimensional rangers are extremely common on mobile robotics platforms. Three dimensional systems are used on high end robotics systems, but they are less common because they are extremely expensive relative to one and two dimensional systems.
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Table of Contents
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Distance Measurement
Interferometry
"Interferometry is the technique of diagnosing the properties of two or more waves by studying the pattern of interference created by their superposition." wikipedia
I am searching for information on how this method is used for distance measurement.
Time of Flight
Time of Flight (TOF) measurement is the one of the simplest distance measurement technique that is commonly used. The device sends a signal towards the area of interest. If there is an object in range, the signal is bounced back towards the device where it is received. The combined time for the signal to leave and return is measured and compared to the known velocity of the signal to determine the distance between the device and the object. This method is commonly implemented with sound waves ,but it can also use other wave types. This type of measurement requires a dedicated computer.
Geometrical
Geometrical Distance measurement is arguably as simple as time of flight. A signal is broadcast and the location of the returning signal is measured. The distance from the object that caused the signal to return can be found through triangulation of the source, the return point, and the object. This system often comes in an infrared form (i.e. Sharp GPD2 12 13). The returning signal lands on some type of a transistor that converts the returning location to an electrical signal. This method requires almost no processing power for the measurement to be taken allowing for the individual units to be very cost effective.
System Configuration
One-Dimensional
A one dimensional LIDAR system can be used alone or as the building block of a more advanced configuration. One dimensional systems are used where distance measurement is needed in a single line of sight.
Two-Dimensional
A two dimensional LIDAR system consists of a one dimensional ranger that changes angle to produce a sweeping scan. Distance measurements are taken periodically as the angle changes to form a type of polar data describing the surroundings.
The two dimensional
Three-Dimensional
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Products
SICK
SICK is a German company that specializes in remote sensing technology. SICK has become the industry leader in high end laser ranging technology. They produce one, two, and three dimensional laser rangers.
The LMS 291 is 2D laser ranger that is commonly used on large mobile robotics platforms. The unit uses interferometry along with a spinning mirror the retrieve and 180 degree sweeping scan with single degree precision. The LMS 291 has a working range between much less than a meter and 40 meters, however this range is broken into sets so it can not be used continuously. The LMS 291 communicates to a PC via serial rs232.
