Reliability analysis of transform-based stereo matching techniques, and a new matching constraint

Stereo vision is a method of depth perception, in which depth information is inferred from two (or more) images of a scene, taken from different perspectives. Practical applications for stereo vision include aerial photogrammetry, autonomous vehicle guidance, robotics and industrial automation. The initial motivation behind this work was to produce a stereo vision sensor for mining automation applications. For such applications, the input stereo images would consist of close range scenes of rocks. A fundamental problem faced by matching algorithms is the matching or correspondence problem. This problem involves locating corresponding points or features in two images. For this application, speed, reliability, and the ability to produce a dense depth map are of foremost importance. This work implemented a number of areabased matching algorithms to assess their suitability for this application. Area-based techniques were investigated because of their potential to yield dense depth maps, their amenability to fast hardware implementation, and their suitability to textured scenes such as rocks. In addition, two non-parametric transforms, the rank and census, were also compared. Both the rank and the census transforms were found to result in improved reliability of matching in the presence of radiometric distortion - significant since radiometric distortion is a problem which commonly arises in practice. In addition, they have low computational complexity, making them amenable to fast hardware implementation. Therefore, it was decided that matching algorithms using these transforms would be the subject of the remainder of the thesis. An analytic expression for the process of matching using the rank transform was derived from first principles. This work resulted in a number of important contributions. Firstly, the derivation process resulted in one constraint which must be satisfied for a correct match. This was termed the rank constraint. The theoretical derivation of this constraint is in contrast to the existing matching constraints which have little theoretical basis. Experimental work with actual and contrived stereo pairs has shown that the new constraint is capable of resolving ambiguous matches, thereby improving match reliability. Secondly, a novel matching algorithm incorporating the rank constraint has been proposed. This algorithm was tested using a number of stereo pairs. In all cases, the modified algorithm consistently resulted in an increased proportion of correct matches. Finally, the rank constraint was used to devise a new method for identifying regions of an image where the rank transform, and hence matching, are more susceptible to noise. The rank constraint was also incorporated into a new hybrid matching algorithm, where it was combined a number of other ideas. These included the use of an image pyramid for match prediction, and a method of edge localisation to improve match accuracy in the vicinity of edges. Experimental results obtained from the new algorithm showed that the algorithm is able to remove a large proportion of invalid matches, and improve match accuracy.

Spatial mapping and map exploitation : a bio-inspired engineering perspective

Probabilistic robot mapping techniques can produce high resolution, accurate maps of large indoor and outdoor environments. However, much less progress has been made towards robots using these maps to perform useful functions such as efficient navigation. This paper describes a pragmatic approach to mapping system development that considers not only the map but also the navigation functionality that the map must provide. We pursue this approach within a bio-inspired mapping context, and use esults from robot experiments in indoor and outdoor environments to demonstrate its validity. The research attempts to stimulate new research directions in the field of robot mapping with a proposal for a new approach that has the potential to lead to more complete mapping and navigation systems.

Performance evaluation of an adaptive travel time prediction model

This paper presents a travel time prediction model and evaluates its performance and transferability. Advanced Travelers Information Systems (ATIS) are gaining more and more importance, increasing the need for accurate, timely and useful information to the travelers. Travel time information quantifies the traffic condition in an easy to understand way for the users. The proposed travel time prediction model is based on an efficient use of nearest neighbor search. The model is calibrated for optimal performance using Genetic Algorithms. Results indicate better performance by using the proposed model than the presently used naïve model.

Twelve-month effectiveness of a parent-led, family-focused weight-management program for prepubertal children : a randomized, controlled trial

BACKGROUND Parenting-skills training may be an effective age-appropriate child behavior-modification strategy to assist parents in addressing childhood overweight. OBJECTIVE Our goal was to evaluate the relative effectiveness of parenting-skills training as a key strategy for the treatment of overweight children. DESIGN The design consisted of an assessor-blinded, randomized, controlled trial involving 111 (64% female) overweight, prepubertal children 6 to 9 years of age randomly assigned to parenting-skills training plus intensive lifestyle education, parenting-skills training alone, or a 12-month wait-listed control. Height, BMI, and waist-circumference z score and metabolic profile were assessed at baseline, 6 months, and 12 months (intention to treat). RESULTS After 12 months, the BMI z score was reduced by ∼10% with parenting-skills training plus intensive lifestyle education versus ∼5% with parenting-skills training alone or wait-listing for intervention. Waist-circumference z score fell over 12 months in both intervention groups but not in the control group. There was a significant gender effect, with greater reduction in BMI and waist-circumference z scores in boys compared with girls. CONCLUSION Parenting-skills training combined with promoting a healthy family lifestyle may be an effective approach to weight management in prepubertal children, particularly boys. Future studies should be powered to allow gender subanalysis.

Empirical investigation of interactive highway safety design model accident prediction algorithm : Rural intersections

One major gap in transportation system safety management is the ability to assess the safety ramifications of design changes for both new road projects and modifications to existing roads. To fulfill this need, FHWA and its many partners are developing a safety forecasting tool, the Interactive Highway Safety Design Model (IHSDM). The tool will be used by roadway design engineers, safety analysts, and planners throughout the United States. As such, the statistical models embedded in IHSDM will need to be able to forecast safety impacts under a wide range of roadway configurations and environmental conditions for a wide range of driver populations and will need to be able to capture elements of driving risk across states. One of the IHSDM algorithms developed by FHWA and its contractors is for forecasting accidents on rural road segments and rural intersections. The methodological approach is to use predictive models for specific base conditions, with traffic volume information as the sole explanatory variable for crashes, and then to apply regional or state calibration factors and accident modification factors (AMFs) to estimate the impact on accidents of geometric characteristics that differ from the base model conditions. In the majority of past approaches, AMFs are derived from parameter estimates associated with the explanatory variables. A recent study for FHWA used a multistate database to examine in detail the use of the algorithm with the base model-AMF approach and explored alternative base model forms as well as the use of full models that included nontraffic-related variables and other approaches to estimate AMFs. That research effort is reported. The results support the IHSDM methodology.

Randomized trial of effect of bifocal and prismatic bifocal spectacles on myopic progression

Objective: To determine whether bifocal and prismatic bifocal spectacles could control myopia in children with high rates of myopic progression. ---------- Methods: This was a randomized controlled clinical trial. One hundred thirty-five (73 girls and 62 boys) myopic Chinese Canadian children (myopia of 1.00 diopters [D]) with myopic progression of at least 0.50 D in the preceding year were randomly assigned to 1 of 3 treatments: (1) single-vision lenses (n = 41), (2) +1.50-D executive bifocals (n = 48), or (3) +1.50-D executive bifocals with a 3–prism diopters base-in prism in the near segment of each lens (n = 46). ---------- Main Outcome Measures: Myopic progression measured by an automated refractor under cycloplegia and increase in axial length (secondary) measured by ultrasonography at 6-month intervals for 24 months. Only the data of the right eye were used. ---------- Results: Of the 135 children (mean age, 10.29 years [SE, 0.15 years]; mean visual acuity, –3.08 D [SE, 0.10 D]), 131 (97%) completed the trial after 24 months. Myopic progression averaged –1.55 D (SE, 0.12 D) for those who wore single-vision lenses, –0.96 D (SE, 0.09 D) for those who wore bifocals, and –0.70 D (SE, 0.10 D) for those who wore prismatic bifocals. Axial length increased an average of 0.62 mm (SE, 0.04 mm), 0.41 mm (SE, 0.04 mm), and 0.41 mm (SE, 0.05 mm), respectively. The treatment effect of bifocals (0.59 D) and prismatic bifocals (0.85 D) was significant (P < .001) and both bifocal groups had less axial elongation (0.21 mm) than the single-vision lens group (P < .001). ---------- Conclusions: Bifocal lenses can moderately slow myopic progression in children with high rates of progression after 24 months.