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ECE5320 Mechatronics Assignment01: Literature Survey on Sensors and Actuators Topic: Sensor: Flash Ladar - PowerPoint PPT Presentation


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ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: Sensor: Flash Ladar. Prepared by: Brandon Boldt Dept. of Electrical and Computer Engineering Utah State University (Electrical and Computer Engineering Dept.). 3/9/2007. Outline . Reference list

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ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Topic: Sensor: Flash Ladar

Prepared by: Brandon Boldt

Dept. of Electrical and Computer Engineering

Utah State University

(Electrical and Computer Engineering Dept.)

3/9/2007


Outline
Outline

  • Reference list

  • To probe further

  • Overview

  • Design Considerations

  • Applications

  • Issues

  • Where to Buy

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Reference list
Reference list

  • S. B. Gokturk, H. Yalcin, and C. Bamji, “A time-of-flight depth sensor – system description, issues and solutions,” 2004 Conference on Computer Vision and Pattern Recognition Workshop.

  • S. B. Gokturk and C. Tomasi, “3d head tracking based on recognition and interpolation using a time-of-flight depth sensor,” 2004 IEEE Computer Society Conference on Computer Vision and Pattern Recognition.

  • Beeck, Wilinski, Fehn, Kauff, Ijsselsteijn, Pollefeys, Gool, Ofek, and Sexton, “Towards an optimized 3D broadcast chain.”

  • Anderson, Herman, and Kelly, “Experimental Characterization of Commercial Flash Ladar Devices”, The Robotics Institute

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


To explore further survival pointers of web references etc
To explore further (survival pointers of web references etc)

  • http://en.wikipedia.org/wiki/Ladar

    A wikipedia entry for Ladar

  • http://www.canesta.com/html/technical_papers.htm

    Canesta's repository of technical papers

  • http://www.csem.ch/fs/imaging.htm

    CSEM's center for imaging

  • http://www.3dvsystems.com/technology/tech.html

    3DV Systems' repository of technical papers

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators


Overview
Overview

  • Ladar stands for “Laser Detection and Ranging.”

  • Ladar is descriptive of all devices which use light waves to determine the distance of objects remotely.

  • The most common type of light used is laser light.

Laser

Ladar System

Object


Overview1

Laser

Ladar System

Object

Overview

  • Ladar System emit a laser with some type of wave function.

  • The laser reflects off of the subject of the system and returns to the ladar system.

  • The ladar system measures phase offset of the returned ladar which is proportional to the distance the ladar traveled.


Overview2
Overview

  • Flash Ladar Systems have an array of sensors in order to capture a scene of 3D points simultaneously. Generally, an optical lens is needed to focus the lasers from the object onto the array of sensors.

Ladar System

Lens

Object

Sensor Array


Design considerations
Design Considerations

  • Unambiguous Range - Because the ladar system measures a phase offset, the system has some ambiguity as multiples of a phase offset of 2 π give the same distance. The unambiguous measurable distance varies with the frequency used in the ladar system.

Ladar System

Possible Object

Possible Object

Possible Object


Design considerations1
Design Considerations

  • Accuracy – An important consideration for any ladar system is the accuracy of the ladar system. Various factors affect this important characteristic and will be discussed here.

Ladar System

Accuracy of Object Location


Design considerations accuracy
Design Considerations: Accuracy

  • Modulation Frequency – increasing the modulation frequency improves the accuracy of the system, but decreases the unambiguous range.

  • Power of the laser – increasing the power of the laser improves the accuracy of the system, but the system will consume more power overall.

  • Ambient light – the less ambient light that is present in the scene, the better the accuracy of the system, however, this may not be a parameter that can be adjusted


Design considerations accuracy1
Design Considerations: Accuracy

  • Field of View – Decreasing the field of view improves the accuracy of the system, but some objects may require multiple shots and be stitched together.

  • Integration Time – Increasing the time the sensor integrates the results will improve the accuracy of the system, but the camera will take more time per shot to capture the data. Also, if the scene is not still, a long integration time can have motion blur.


Applications head tracking
Applications: Head Tracking

  • For security reasons, it is desirable to recognize a person from a database. Flash ladar has been used to characterize 3d features of heads in order to determine the person being captured. The advantage of ladar over visual camera is the ability to easily separate the head from the background.

Laser

Ladar System

Head

Complex Background


Applications robotic vision
Applications: Robotic Vision

  • In many robotic applications, obstical avoidance is a necessary quality. The ability to view the 3D world around the robot is a valuable asset. Flash ladar systems allow robots to capture 3D data quickly and the ability to process the data as a group, rather than individual points.

Ladar System

Mobile Robot

Obstacle


Applications human machine interaction
Applications: Human-Machine Interaction

  • The ability to interpret human movements remotely is an area of interest to developers in variety of industrial fields. Its application could be used in computer peripheral devices as well as hazardous industrial environments. Flash ladar allows developers to quickly capture human data as a group rather than individual points giving a richer environment to work with.

Ladar System

Human


Applications automatic target recognition
Applications: Automatic Target Recognition

  • In combat, the ability to recognize threats over non-threats is crucial. Flash ladar adds a third dimension to camera based target recognition which gives an added advantage when determining the targets on a field.

Ladar System

Tank

Car

Person


Issues noise
Issues: Noise

  • Each pixel of a flash ladar system has a certain amount of noise associated with it. Each pixel value can be modeled as a gaussian variable with a particular mean and a particular standard deviation. To improve the noise of a ladar system, temporal or spatial averaging can be used to decrease the noise assuming the pixels to be averaged together have the same mean value.

Measured pixel value over time

value

mean

time


Issues aliasing
Issues: Aliasing

  • For a particular modulation frequency in a flash ladar system, the system has an unambiguous range. When the scene captured has a dynamic range that is larger than the unambiguous range then aliasing arises as a problem. One method to overcome the unambiguous range is to take two or more measurements with different frequencies. This increases the unambiguous range to the least common multiple of the two previous unambiguous ranges.

Higher Freq.

Lower Freq.

Ladar Sytem

Ladar Sytem

Object

Object


Issues ambient light
Issues: Ambient Light

  • “Ambient Light is considered as unwanted light that has the same wavelength as the light source of the system.” (Gokturk) Ambient Light has the undesired effect of increasing the noise due to interference. In general this effect produces a high-frequency effect, and can be passed through a low-pass filter if thought to be a problem.

Ambient Light

Ladar Sytem

Object


Issues saturation versus no data
Issues: Saturation versus No Data

  • In a flash ladar system, a pixel only produces a valid value if enough light lands on the pixel; however, too much light can saturate the pixel values, which also will cause the pixel to produce an incorrect result. This effects the dynamic range of the scene as well as the reflectivity dyanmics in the scene. One method to overcome this issue is to use multiple shots will different exposure levels and then stitch the two shots together.


Where to buy
Where To Buy

  • Canesta, Inc.

    • http://www.canesta.com

  • Swiss Center for Electronics and Microtechnology

    • http://www.csem.ch/

  • 3DV Systems

    • http://www.3dvsystems.com/


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