3 research outputs found
Stereo panoramic vision for obstacle detection
Statistics show that automotive accidents occur regularly as a result of blind-spots and driver inattentiveness. Such incidents can have a large financial cost associated with them, as well as injury and loss of life. There are several methods currently available to assist drivers in avoiding such collisions. The simplest method is the installation of devices to increase the driver's field of view, such as extra mirrors and wide angle lenses. However, these still rely on an alert human observer and do not completely eliminate blind-spots. Another approach is to use an automated system which utilises sensors such as sonar or radar to gather range information. The range data is processed, and the driver is warned if a collision is immiment. Unfortunately, these systems have low angular resolution and limited sensing volumes. This was the motivation for developing a new method of obstacle detection. In this project, we have designed, built and evaluated a new type of sensor for blind spot monitoring. The stereo panoramic sensor consists of a video camera which views a convex mirrored surface. With the camera and mirror axes aligned, a full 360 degrees can be viewed perpendicular to the sensor axis. Two different mirror profiles were evaluatedthe constant gain, and resolution invariant surfaces. It was found that the constant gain mirror was the most effective for this application. It was shown that the sensor can be used to generate disparity maps from which obstacles can be segmented. This was done by applying the v-disparity algorithm, which has previously not been utilised in panoramic image processing. We found that this method was very powerful for segmenting objects, even the case of extremely noisy data. The average successful obstacle detection rate was found to be around 90%, with a false detecion rate of 8%. Our results indicate that range can be estimated reliably using a stereo panoramic sensor, with excellent angular accuracy in the azimuth direction. In ground truth experiments it was found that the sensor was able to estimate range to within 20cm of the true value, and a maximum angular error of 3°. Through experimentation, we determined that the physical system was approximately half as accurate in comparison to the simulations. However, it should be noted that the system is a prototype which could be developed futher. Nevertheless, this sensor still has the advantage of a much higher angular resolution and larger sensing volume than the driver assistance systems reported to date
Sistema de localização com ultrassons
Doutoramento em Engenharia ElectrotécnicaEsta tese apresenta um sistema de localização baseado exclusivamente em ultrassons,
não necessitando de recorrer a qualquer outra tecnologia. Este sistema
de localização foi concebido para poder operar em ambientes onde qualquer
outra tecnologia não pode ser utilizada ou o seu uso está condicionado,
como são exemplo aplicações subaquáticas ou ambientes hospitalares. O sistema
de localização proposto faz uso de uma rede de faróis fixos permitindo
que estações móveis se localizem. Devido à necessidade de transmissão de
dados e medição de distâncias foi desenvolvido um pulso de ultrassons robusto
a ecos que permite realizar ambas as tarefas com sucesso. O sistema
de localização permite que as estações móveis se localizem escutando apenas
a informação em pulsos de ultrassons enviados pelos faróis usando para
tal um algoritmo baseado em diferenças de tempo de chegada. Desta forma
a privacidade dos utilizadores é garantida e o sistema torna-se completamente
independente do número de utilizadores. Por forma a facilitar a implementação
da rede de faróis apenas será necessário determinar manualmente a posição
de alguns dos faróis, designados por faróis âncora. Estes irão permitir que os
restantes faróis, completamente autónomos, se possam localizar através de um
algoritmo iterativo de localização baseado na minimização de uma função de
custo. Para que este sistema possa funcionar como previsto será necessário
que os faróis possam sincronizar os seus relógios e medir a distância entre eles.
Para tal, esta tese propõe um protocolo de sincronização de relógio que permite
também obter as medidas de distância entre os faróis trocando somente três
mensagens de ultrassons. Adicionalmente, o sistema de localização permite que
faróis danificados possam ser substituÃdos sem comprometer a operabilidade da
rede reduzindo a complexidade na manutenção. Para além do mencionado, foi
igualmente implementado um simulador de ultrassons para ambientes fechados,
o qual provou ser bastante preciso e uma ferramenta de elevado valor para simular
o comportamento do sistema de localização sobre condições controladas.This thesis presents a location system based exclusively on ultrasonic signals,
without using any other technology. This location system was designed to operate
in environments where the use of other technologies is not possible or the
use of them is limited, such as underwater applications or hospital environments.
The proposed location system uses a network of fixed beacons allowing the mobile
stations to locate. Due to the necessity of data transmission and distance
measurement an ultrasonic pulse robust to echoes was developed that allows
to perform both tasks with success. The location system allows that mobiles locate
themselves only listening to the information in the ultrasonic pulse sent by
the beacons, for that an algorithm based on time difference of arrival is used.
Therefore, the user privacy is guaranteed as well as the complete independence
of the system number of users. To simplify the network implementation it is only
necessary to manually define the position of some of the beacons, called anchor
beacons. These will allow the remaining autonomous beacons to locate themselves
by an iterative location algorithm based on a local cost function minimization.
For this system to work properly the beacons must synchronize their clocks
and measure the distance between them. Therefore, this thesis proposes a clock
synchronization protocol which also allows to measure the distance between the
beacons by exchanging only three ultrasonic messages. Additionally, the location
system permits that damaged beacons may be replaced without compromising
the network operability reducing the maintenance complexity. Additionally, a simplified
ultrasonic simulator for indoor environments was developed, which has
proved to be very accurate and a valuable tool to simulate the location system
behavior under controlled conditions