Moving Observers in an Isotropic Universe

We show how the anisotropy resulting from the motion of an observer in an isotropic universe may be determined by measurements. This provides a means to identify inertial frames, yielding a simple resolution to the twins paradox of relativity theory. We propose that isotropy is a requirement for a frame to be inertial; this makes it possible to relate motion to the large scale structure of the universe.Comment: 8 pages, 1 figure, with minor typographical correctio

Vision-Guided Mobile Robot Navigation

This report discusses the use of vision feedback for autonomous navigation by a mobile robot in indoor environments. In particular, we have discussed in detail the issues of camera calibration and how binocular and monocular vision may be utilized for self-location by the robot. A noteworthy feature of monocular vision is that the camera image is compared with a CAD model of the interior of the hallways using the PSEIKI reasoning system; this reasoning system allows the comparison to take place at different levels of geometric detail

Imaging with Diffraction Tomography

The problem of cross sectional (tomographic) imaging bf objects with diffracting sources is addressed. Specifically the area of investigation is the effect of multiple scattering and attenuation phenomena in diffraction imaging. This work reviews the theory and limits of first order diffraction tomography and studies iterative techniques that can be used to improve the quality of tomographic imaging with diffracting sources. Conventional (straight-ray) tomographic algorithms are not valid when used with acoustic or microwave energy. Thus more sophisticated algorithms are needed; First order diffraction tomography uses a linearized version of the wave equation and gives an especially simple reconstruction algorithm. This work reviews first order approximations to the scattered field and studies the quality of the reconstructions when the assumptions behind these approximations are violated. It will be shown that the Born approximation is valid when the phase change across the object is less than it and the Rytov approximation is valid when the refractive index changes by less than two or three percent. Better reconstructions will be based on higher order approximations to the scattered field. This work describes two fixed point algorithms (the Born and the Rytov approximations) and an algebraic approach to more accurately calculate the scattered fields. The limits of each of these approaches is discussed and simulated results are shown. Finally a review of higher order inversion techniques is presented. Each of these techniques is reviewed and some of their limitations are discussed

Rule-Based Approach to Binocular Stereopsis

This research is motivated by a desire to integrate some of the diverse, yet complimentary, developments that have taken place during the past few years in the area of passive stereo vision. On the one hand, we have approaches based on matching zero-crossings along epipolar lines, and, on the other, people have proposed techniques that match directly higher level percepts, such as line elements and other geometrical forms. Our rule-based program is a modest attempt at integrating these different approaches into a single program. Such integration was made necessary by the fact that no single method by itself appears capable of generating usable range maps of a scene

Multiple Scattering and Attenuation Phenomena in Diffraction Imaging

The problem of cross sectional (tomographic) imaging bf objects with diffracting sources is addressed. Specifically the area of investigation is the effect of multiple scattering and attenuation phenomena in diffraction imaging. The validity of either the Born or the Rytov approximations is the basic assumption behind all the inverse scattering techniques in diffraction tomography. To test these techniques When these assumptions are not satisfied, we have developed a computational procedure for the calculation of the “ true” scattered fields from a multi-component object. Using this procedure, the performance of two available diffraction reconstruction techniques is examined in the presence of multiple scattering effects. The simulation results show the superiority of the Synthetic Aperture technique. We have also studied the role of attenuation in the reconstruction techniques. To calculate the scattered fields from an object in the presence of attenuation, new computer simulation programs are developed. These codes are used in a simulation study of the effect of the attenuation parameter on the object reconstuctions. [reconstruction

3D-POLY: A Robot Vision System for Recognizing Objects in Occluded Environments

The two factors that determine the time complexity associated with model-driven interpretation of range maps are: I) the particular strategy used for the generation of object hypotheses; and 2) the manner in which both the model and the sensed data are organized, data organization being a primary determinant of the efficiency of verification of a given hypothesis. In this report, we present 3D-POLY, a working system for recognizing objects in the presence of occlusion and against cluttered backgrounds. The time complexity of this system is only O(n2) for single object recognition, where n is the number of features on the object. The most novel aspect of this system is the manner in which the feature data are organized for the models. We use a data structure called the feature sphere for the purpose. We will present efficient algorithms for assigning a feature to its proper place on a feature sphere, and for extracting the neighbors of a given feature from the feature sphere representation. For hypothesis generation, we use local feature sets, a notion similar to those used before us by Bolles, Shirai and others. The combination of the feature sphere idea for streamlining verification and the local feature sets for hypothesis generation results in a system whose time complexity has a polynomial bound. In addition to recognizing objects in occluded environments, 3D-POLY also possesses model learning capability. Model learning consists of looking at a model object from different views and integrating the resulting information. The 3D-POLY system also contains utilities for range image segmentation and classification of scene surfaces

Reflection Mode Diffraction Tomography

In the field of ultrasound diffraction tomography, a cross section of a weakly scattering object is reconstructed from measurements of the sound scattered from the insonified object. This research studies tomographic imaging algorithms that deal only with the sound that is backscattered from the object. The use of the backscattered sound provides higher resolution reconstructions due to the higher spatial frequency information about the object that is obtained from the backscatter. Unfortunately the cost of the high frequency information contained in the backscatter is the loss of low frequency information. Different approaches to compensate for this loss are discussed. An additional benefit of reflection mode tomography is that it has the advantage of requiring only 180° access to the object whereas transmission mode requires 360°. The charter of this research is to explore the effectiveness of current reflection mode diffraction tomography algorithms and to theoretically develop, as well as experimentally verify, new algorithms. Different scanning geometries with different methods of insonification are explored. Many different approaches to the analysis of the problem are taken

Task Planner for Simultaneous Fulfillment of Operational, Geometric and Uncertainty-Reduction Goals

Our ultimate goal in robot planning is to develop a planner which can create complete assembly plans given as input a high level description of assembly goals, geometric models of the components of the assembly, and a description of the capabilities of the work cell (including the robot and the sensory system). In this paper, we introduce SPAR, a planning system which reasons about high level operational goals, geometric goals and uncertainty-reduction goals in order to create assembly plans which consist of manipulations as well as sensory operations when appropriate. Operational planning is done using a nonlinear, constraint posting planner. Geometric planning is accomplished by constraining the execution of operations in the plan so that geometric goals are satisfied, or, if the geometric configuration of the world prevents this, by introducing new operations into the plan with the appropriate constraints. When the uncertainty in the world description exceeds that specified by the uncertainty-reduction goals, SPAR introduces either sensing operations or manipulations to reduce that uncertainty to acceptable levels. If SPAR cannot find a way to sufficiently reduce uncertainties, it does not abandon the plan. Instead, it augments the plan with sensing operations to be used to verify the execution of the action, and, when possible, posts possible error recovery plans, although at this point, the verification operations and recovery plans are predefined

Tutorial on Lisp Object- Oriented Programming for Blackboard Computation (Solving the Radar Tracking Problem)

This exposition is a tutorial on how object-oriented programming in Lisp can be used for programming a blackboard. Since we have used Franz Lisp and since object oriented programming in Franz is carried out via flavors, the exposition demonstrates how flavors can be used for this purpose. The reader should note that the different approaches to object-oriented programming share considerable similarity and, therefore, the exposition should be helpful to even those who may not wish to use flavors. We have used the radar tracking problem as a ‘medium’ for explaining the concepts underlying blackboard programming. The blackboard database is constructed solely of flavors which act as data structures as well as method-bearing objects. Flavor instances form the nodes and the levels of the blackboard. The methods associated with these flavors constitute a distributed monitor and support the knowledge sources in modifying the blackboard data. A rule-based planner is used to construct knowledge source activation records from the goals residing in the blackboard. These activation records are enqueued in a cyclic queueing system. A scheduler cycles through the queues and selects knowledge sources to fir

PSEIKI: A Production System Environment for Integrating Knowledge with Images

A description of work-in-progress on PSEIKI is presented. PSEIKI is a computer vision system designed to use multiple sources of knowledge to aid in the image understanding task. In this report we describe the concepts used in PSEIKI and how the incorporation of world knowledge is used to make PSEIKI expectation driven. The world knowledge in the system is represented as a line drawing of the expected scene. The system is implemented as a 2 panel / 6 level blackboard and uses the Dempster-Shafer formalism to accomplish inexact reasoning in a hierarchical spac