\section{Conclusions}
To meet the proposed objectives, a study of the state of the art on odometry solutions was developed. After that, a study was made to find the most suitable solution for the problem and due to the advantages of flexibility, a visual odometry with a line scan image sensor was the solution chosen for study.

Visual odometry with line scan sensors is a new area of study and very little literature exists. So the main objective of this wotk was to find out the problems, limitations and the relevant variables for the operation of this method. 

It was proven that a line scan image sensor can operate as a velocity sensor under controlled conditions for lighting and absence of vibration. Under these conditions the sensor can estimate velocity with low error, about 1$\%$ on most of the cases. The sensor performed well for straight line movements with the camera aligned and misaligned up to a maximum of 10$^{\circ}$. For circular movements the sensor performed well and showed that it is possible to operate when an automobile is executing maneuvers with a tight turning radius. For situations when the focal distance is changing the results were satisfactory for concrete and cork although they were poor for stone. This is a limitation for the hardware used and can be improved using appropriate optics.

This method creates new possibilities for visual odometry. The most limiting features of common visual odometry are the low velocity that can be estimated, due to low frame rates of the common cameras; the complexity of the algorithms which are needed to be used causing high computational cost and difficulty of real time application. The line scan sensor needs less complex algorithms and can easily achieve high frame rates necessary to measure high velocities.

The method shows promising results and further investigation and development should be performed in order to study the applicability in real world scenarios.

\section{Future Work}

The results from this work showed that using a line scan sensor to measure velocity of a automobile is possible in controlled conditions. The results are promising and further investigation should be developed. Several variables should be investigated, like the effect of lighting variation; the effect of introducing vibration and the effect of changing the focal distance. Outdoors experiments should also be realized with all those variables introduced in the environment.

The optics used performed acceptably with variable focal length. Although to improve even more the consistency of the measurements telecentric lens may be used, this lens have a magnification that is invariable with the focal distance. This means that even when with irregular ground or with oscillations from the vehicle suspension, the estimates will be more precise. Other solution for high focal distance variations might be a combination of several lenses, each calibrated to operate at a specific distance. Then, the equipment along with the distance information from another sensor, like a laser sensor, can commute between the lenses to use the one most appropriated for the current distance.

To ensure that this method has good performance when dealing with circular movements, the image sensor should be as tangential as possible to the line of movement. When the image sensor is not tangent that means that the line scans will have a lateral displacement; an high lateral displacement will eventually cause the system to fail computing the correct longitudinal displacement. To ensure that the image sensor is always tangent to the line of movement, a system using a servo motor relaying on the gyroscopes readings can be used to align the image sensor. Basically the image sensor would be mounted on a servo motor that would change its orientation as much as the rotation given by the gyroscopes. 

The use of an image sensor with higher sensitivity should be considered. In this work the acquisition rate was limited to 2500 $Hz$ due to the lack of brightness on the images. This was caused by the low exposure time, causing the images to be dark. To solve this, a higher sensitivity image sensor should be used to not compromise the quality of the images at high frame rates. 

In a real world scenario infra-red lighting can be used, as this type of light is invisible to the human eye. This is important if the sensor is to be used by automobiles on the public roads; it is important that the lighting for the sensor isn't a distraction for the drivers. Also, the artificial infra-red lighting should be able overcome the infra-red radiation from the sun. This is important as the radiation from the sun varies throughout the day and the lighting should be as invariable as possible. Then the image sensor should be sensitive to the wavelength of the infra-red radiation.

