The authors describe a general-purpose, representation-independent method for the accurate and computationally efficient registration of 3-D shapes including free-form curves and surfaces. The method handles the full six degrees of freedom and is based on the iterative closest point (ICP) algorithm, which requires only a procedure to find the closest point on a geometric entity to a given point. The ICP algorithm always converges monotonically to the nearest local minimum of a mean-square distance metric, and the rate of convergence is rapid during the first few iterations. Therefore, given an adequate set of initial rotations and translations for a particular class of objects with a certain level of 'shape complexity', one can globally minimize the mean-square distance metric over all six degrees of freedom by testing each initial registration. One important application of this method is to register sensed data from unfixtured rigid objects with an ideal geometric model, prior to shape inspection. Experimental results show the capabilities of the registration algorithm on point sets, curves, and surfaces. >

A method for registration of 3-D shapes

Clustering is the unsupervised classification of patterns (observations, data items, or feature vectors) into groups (clusters). The clustering problem has been addressed in many contexts and by researchers in many disciplines; this reflects its broad appeal and usefulness as one of the steps in exploratory data analysis. However, clustering is a difficult problem combinatorially, and differences in assumptions and contexts in different communities has made the transfer of useful generic concepts and methodologies slow to occur. This paper presents an overview of pattern clustering methods from a statistical pattern recognition perspective, with a goal of providing useful advice and references to fundamental concepts accessible to the broad community of clustering practitioners. We present a taxonomy of clustering techniques, and identify cross-cutting themes and recent advances. We also describe some important applications of clustering algorithms such as image segmentation, object recognition, and information retrieval.

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Data clustering: a review

Machine Learning is the study of methods for programming computers to learn. Computers are applied to a wide range of tasks, and for most of these it is relatively easy for programmers to design and implement the necessary software. However, there are many tasks for which this is difficult or impossible. These can be divided into four general categories. First, there are problems for which there exist no human experts. For example, in modern automated manufacturing facilities, there is a need to predict machine failures before they occur by analyzing sensor readings. Because the machines are new, there are no human experts who can be interviewed by a programmer to provide the knowledge necessary to build a computer system. A machine learning system can study recorded data and subsequent machine failures and learn prediction rules. Second, there are problems where human experts exist, but where they are unable to explain their expertise. This is the case in many perceptual tasks, such as speech recognition, hand-writing recognition, and natural language understanding. Virtually all humans exhibit expert-level abilities on these tasks, but none of them can describe the detailed steps that they follow as they perform them. Fortunately, humans can provide machines with examples of the inputs and correct outputs for these tasks, so machine learning algorithms can learn to map the inputs to the outputs. Third, there are problems where phenomena are changing rapidly. In finance, for example, people would like to predict the future behavior of the stock market, of consumer purchases, or of exchange rates. These behaviors change frequently, so that even if a programmer could construct a good predictive computer program, it would need to be rewritten frequently. A learning program can relieve the programmer of this burden by constantly modifying and tuning a set of learned prediction rules. Fourth, there are applications that need to be customized for each computer user separately. Consider, for example, a program to filter unwanted electronic mail messages. Different users will need different filters. It is unreasonable to expect each user to program his or her own rules, and it is infeasible to provide every user with a software engineer to keep the rules up-to-date. A machine learning system can learn which mail messages the user rejects and maintain the filtering rules automatically. Machine learning addresses many of the same research questions as the fields of statistics, data mining, and psychology, but with differences of emphasis. Statistics focuses on understanding the phenomena that have generated the data, often with the goal of testing different hypotheses about those phenomena. Data mining seeks to find patterns in the data that are understandable by people. Psychological studies of human learning aspire to understand the mechanisms underlying the various learning behaviors exhibited by people (concept learning, skill acquisition, strategy change, etc.).

Machine learning

We describe a technique for image encoding in which local operators of many scales but identical shape serve as the basis functions. The representation differs from established techniques in that the code elements are localized in spatial frequency as well as in space. Pixel-to-pixel correlations are first removed by subtracting a lowpass filtered copy of the image from the image itself. The result is a net data compression since the difference, or error, image has low variance and entropy, and the low-pass filtered image may represented at reduced sample density. Further data compression is achieved by quantizing the difference image. These steps are then repeated to compress the low-pass image. Iteration of the process at appropriately expanded scales generates a pyramid data structure. The encoding process is equivalent to sampling the image with Laplacian operators of many scales. Thus, the code tends to enhance salient image features. A further advantage of the present code is that it is well suited for many image analysis tasks as well as for image compression. Fast algorithms are described for coding and decoding.

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The Laplacian Pyramid as a Compact Image Code

A theory of edge detection is presented. The analysis proceeds in two parts. (1) Intensity changes, which occur in a natural image over a wide range of scales, are detected separately at different scales. An appropriate filter for this purpose at a given scale is found to be the second derivative of a Gaussian, and it is shown that, provided some simple conditions are satisfied, these primary filters need not be orientation-dependent. Thus, intensity changes at a given scale are best detected by finding the zero values of delta 2G(x,y)*I(x,y) for image I, where G(x,y) is a two-dimensional Gaussian distribution and delta 2 is the Laplacian. The intensity changes thus discovered in each of the channels are then represented by oriented primitives called zero-crossing segments, and evidence is given that this representation is complete. (2) Intensity changes in images arise from surface discontinuities or from reflectance or illumination boundaries, and these all have the property that they are spatially. Because of this, the zero-crossing segments from the different channels are not independent, and rules are deduced for combining them into a description of the image. This description is called the raw primal sketch. The theory explains several basic psychophysical findings, and the operation of forming oriented zero-crossing segments from the output of centre-surround delta 2G filters acting on the image forms the basis for a physiological model of simple cells (see Marr & Ullman 1979).

http://www.hms.harvard.edu/bss/neuro/bornlab/qmbc/beta/day4/marr-hildreth-edge-prsl1980.pdf

Theory of Edge Detection

In order to construct algorithmic solutions to the problem of geolocalization of user-generated photographs and videos, one must first populate a geographic database with the different types of objects and markings that are likely to be seen in the photographs and videos. Toward that end, this paper presents a framework for detecting and labeling objects in satellite imagery. The objects that we are interested in are characterized by low-level features that exist mostly at or beyond the limits of spatial resolution in the satellite images. To deal with the challenges posed by the extraction of such features from satellite imagery, we confine our search to the vicinity of the OpenStreetMap (OSM) delineated roads in a geographic area. The OSM roads are projected into the satellite images through inverse orthorectification. As an illustration of the performance of the object detection framework presented in this paper, our system can detect pedestrian crosswalks in a 200000 sq. km. region of Australia (that is covered by 222 satellite images) with a recall rate of 63% and a precision of 89% (evaluated on a 100 sq. km. subregion). All of the computer processing for this result takes a total of 6 h on our in-house cloud computing framework that consists of five nodes, each an off-the-shelf high-end PC class workstation.

A Generic Road-Following Framework for Detecting Markings and Objects in Satellite Imagery

The present invention describes a process, system and computer program product for assessing the modularity of an object-oriented program. The process includes calculation of metrics associated with various properties of the object-oriented program. Analysis is performed on the basis of the calculated metrics.

Process and system for assessing modularity of an object-oriented program

Energy efficiency dominates practically every aspect of the design of a wireless sensor network and duty cycling is an important tool for achieving high energy efficiencies. Duty cycling for wireless camera networks meant for tracking objects is made complex by the nodes having to anticipate the arrival of the objects in their field-of-view. The consequences of an object arriving in the view-region of a camera when it is sleeping need no elaboration. Our work presents a predictive framework to provide nodes with an ability to anticipate the arrival of objects in the field-of-view of their cameras. Our predictive framework differs from others in that the nodes whose duty cycles are increased are at least one step removed from the immediate neighborhood of the nodes where the objects are currently visible. By eliminating the need for the currently busiest nodes to also be in charge of informing their nonbusy immediate neighbors to get ready for object arrival, we end up with a more robust strategy for updating the duty cycle at the nodes where the objects are highly likely to appear soon. The proposed scheme works by using an existing MAC header bit that is already in the 802.15.4 protocol and, in that sense, our anticipatory approach for notifying the nodes about the current state of the object location entails no additional expenditure of energy. Our contribution includes evaluations based on large-scale simulations as well as real experiments with an Imote2-based wireless camera network.

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A predictive duty cycle adaptation framework using augmented sensing for wireless camera networks

Planar homography estimation is foundational to many computer vision problems, such as Simultaneous Localization and Mapping (SLAM) and Augmented Reality (AR). However, conditions of high variance confound even the state-of-the-art algorithms. In this report, we analyze the performance of two recently published methods using Convolutional Neural Networks (CNNs) that are meant to replace the more traditional feature-matching based approaches to the estimation of homography. Our evaluation of the CNN based methods focuses particularly on measuring the performance under conditions of significant noise, illumination shift, and occlusion. We also measure the benefits of training CNNs to varying degrees of noise. Additionally, we compare the effect of using color images instead of grayscale images for inputs to CNNs. Finally, we compare the results against baseline feature-matching based homography estimation methods using SIFT, SURF, and ORB. We find that CNNs can be trained to be more robust against noise, but at a small cost to accuracy in the noiseless case. Additionally, CNNs perform significantly better in conditions of extreme variance than their feature-matching based counterparts. With regard to color inputs, we conclude that with no change in the CNN architecture to take advantage of the additional information in the color planes, the difference in performance using color inputs or grayscale inputs is negligible. About the CNNs trained with noise-corrupted inputs, we show that training a CNN to a specific magnitude of noise leads to a "Goldilocks Zone" with regard to the noise levels where that CNN performs best.

Homography Estimation with Convolutional Neural Networks Under Conditions of Variance.

Our work provides a fast approach-path-independent framework for the problem of place recognition and robot localization in indoor environments. The approach-path independence is achieved by using highly viewpoint-invariant 3D junction features extracted from stereo pairs of images; these are based on stereo reconstructions of the JUDOCA junctions extracted from the individual images of a stereo pair. The speed in place-recognition and robot-localization is achieved by using a novel cylindrical data structure - we refer to it as the Feature Cylinder - for representing either all of the 3D junction features found in a hallway system during the learning phase of the robot or a set of locale signatures derived from the data. For the case when all data is placed on the Feature Cylinder, we can use the 3D-POLY polynomial-time in a hypothesize-and-verify approach to place recognition. On the other hand, in the locale signature based approach, we can use the same data structure for constant-time place recognition.

/pdf/an-approach-path-independent-framework-for-place-recognition-58tk22zpmd.pdf

Avinash C. Kak

Papers

A Generic Road-Following Framework for Detecting Markings and Objects in Satellite Imagery

Process and system for assessing modularity of an object-oriented program

A predictive duty cycle adaptation framework using augmented sensing for wireless camera networks

Homography Estimation with Convolutional Neural Networks Under Conditions of Variance.

An approach-path independent framework for place recognition and mobile robot localization in interior hallways