Showing papers by "French Institute for Research in Computer Science and Automation published in 1987"

Using Canny's criteria to derive a recursively implemented optimal edge detector

Abstract: A highly efficient recursive algorithm for edge detection is presented. Using Canny's design [1], we show that a solution to his precise formulation of detection and localization for an infinite extent filter leads to an optimal operator in one dimension, which can be efficiently implemented by two recursive filters moving in opposite directions. In addition to the noise truncature immunity which results, the recursive nature of the filtering operations leads, with sequential machines, to a substantial saving in computational effort (five multiplications and five additions for one pixel, independent of the size of the neighborhood). The extension to the two-dimensional case is considered and the resulting filtering structures are implemented as two-dimensional recursive filters. Hence, the filter size can be varied by simply changing the value of one parameter without affecting the time execution of the algorithm. Performance measures of this new edge detector are given and compared to Canny's filters. Various experimental results are shown.

Shapes and Geometries: Analysis, Differential Calculus, and Optimization

Abstract: This book provides a self-contained presentation of the mathematical foundations, constructions, and tools necessary for studying problems where the modeling, optimization, or control variable is no longer a set of parameters or functions but the shape or the structure of a geometric object. Shapes and Geometries: Analysis, Differential Calculus, and Optimization presents the extensive, recently developed theoretical foundation to shape optimization in a form that can be used by the engineering community. It also clearly explains the state-of-the-art developments in a mathematical language that will attract mathematicians to open questions in this important field.

IFO: a formal semantic database model

Abstract: A new, formally defined database model is introduced that combines fundamental principles of “semantic” database modeling in a coherent fashion. Using a graph-based formalism, the IFO model provides mechanisms for representing structured objects, and functional and ISA relationships between them. A number of fundamental results concerning semantic data modeling are obtained in the context of the IFO model. Notably, the types of object structure that can arise as a result of multiple uses of ISA relationships and object construction are described. Also, a natural, formal definition of update propagation is given, and it is shown that (under certain conditions) a correct update always exists.

On the representation and querying of sets of possible worlds

Abstract: We represent a set of possible worlds using an incomplete information database. The representation techniques that we study form a hierarchy, which generalizes relations of constants. This hierarchy ranges from the very simple Codd-table, (i e , a relation of constants and distinct variables called nulls, which stand for values present but unknown), to much more complex mechanisms involving views on conditioned-tables, (i e , queries on Codd-tables together with conditions). The views we consider are the queries that have polynomial data-complexity on complete information databases. Our conditions are conjunctions of equalities and inequalities.(1) We provide matching upper and lower bounds on the data-complexity of testing containement, membership, and uniqueness for sets of possible worlds and we fully classify these problems with respect to our representation hierarchy. The most surprising result in this classification is that it is complete in P2p, whether a set of possible worlds represented by a Codd-table is a subset of a set of possible worlds represented by a Codd-table with one conjuction of inequalities.(2) We investigate the data-complexity of querying incomplete information databases. We examine both asking for certain facts and for possible facts. Our approach is algebraic but our bounds also apply to logical databases. We show that asking for a certain fact is coNP-complete, even for a fixed first order query on a Codd-table. We thus strengthen a lower bound of [16], who showed that this holds for a Codd-table with a conjunction of inequalities. For each fixed positive existential query we present a polynomial algorithm solving the bounded possible fact problem of this query on conditioned-tables. We show that our approach is, in a sense, the best possible, by deriving two NP-completeness lower bounds for the bounded possible fact problem when the fixed query contains either negation or recursion.

A local based approach for path planning of manipulators with a high number of degrees of freedom

Abstract: This paper presents an alternative to the Potential Field Method of computing local collision-free motions for general manipulators. The main distinction is that we separate the description of the task from constraints of anti-collision. This enables to control accurately all relevant measures of the problem. A task is expressed by the minimization of a function plus eventually some geometric constraints, whereas anti-collision is translated into very simple linear constraints through the methods of the velocity dampers and the tangent separating planes. This approach is applied to the control of manipulators with a high number of degrees of freedom, using hierarchical descriptions of the environment and the robots. This is illustrated by two realizations, path planning for a ten link manipulator in the cluttered environment of a nuclear plant reactor, and cooperative tasks between two six degree of freedom robots. In the end we discuss how to incorporate the action of a global planner in this general framework.

The asymptotic local approach to change detection and model validation

Abstract: We present a systematic approach for the design of change detection and model validation algorithms for dynamical systems. We show how to associate to any identification algorithm a change detection and a model validation procedure, which are optimal in some asymptotic sense. The foundations of our method go back to the asymptotic local approach in statistics, and our method generalizes this approach.

Efficient registration of stereo images by matching graph descriptions of edge segments

Abstract: We present a new approach to the stereo-matching problem. Images are individually described by aneighborhood graph of line segments coming from a polygonal approximation of the contours. The matching process is defined as the exploration of the largest components of adisparity graph built from the descriptions of the two images, and is performed by an efficient prediction and propagation technique. This approach was tested on a variety of man-made environments, and it appears to be fast and robust enough for mobile robot navigation and three-dimensional part-positioning applications.

SIGNAL: A declarative language for synchronous programming of real-time systems

Abstract: We present an applicative language, SIGNAL, designed to program real-time systems. The language is based on a synchronous notion of time. We assume the execution of operations to have a zero logical time duration; then, the sequence of communication events determines entirely a temporal reference. The ordering of the runable operations is limited only by the dependencies between the calculi : this is the point of view of data flow languages. SIGNAL is a data flow language (where the potential parallelism is implicit), which permits a structural description of interconnected processes. SIGNAL handles possibly infinite sequences of values (called signals) characterized by an implicit clock which specifies the relative instants (with respect to other signals) at which these values are available. Specific operators, such as delay, undersampling, deterministic merge, are designed to express temporal relations between different signals : in this way, a SIGNAL program expresses both functional and temporal relationships between all the involved signals. The language is semantically sound, and its declarative style allows to derive, by a simple projection on the commutative field Z/3Z, a complete static calculus of the timing of any SIGNAL process, called its clock calculus. Hence, the language SIGNAL is also a formal system to reason about timing and concurrency. The clock calculus is completed together with the dependency analysis of a given program. This leads to a conditional dependence graph in which the edges may be labelled by the involved clocks. From this graph, we generate code for a sequential machine, but it appears to be the suitable level to study the implementation on a multiprocessor architecture.

Design of adaptive algorithms for the tracking of time‐varying systems

Abstract: The design of adaptive algorithms for the purpose of the tracking of slowly time varying systems is investigated . A criterion for measuring the tracking capability of an algorithm in this situation was introduced in an earlier work; the domain of vali dity of this criterion is shown to be much wider than expected before. On the other hand, multistep algorithms, introduced in the Soviet literature, are generalized and systematically studied; they are shown to provide significant improvements over the classical (one-step) methods for the purpose of tracking. Finally, a complete design me thodology for adaptive algorithms used on time varying systems is given.

An overview of the multi-database manipulation language MDSL

Abstract: With the increase in availability of databases, data needed by a user are frequently in separate autonomous databases. The logical properties of such data differ from the classical ones within a single database. In particular, they call for new functions for data manipulation. MDSL is a new data manipulation language providing such functions. Most of the MDSL functions are not available in other languages.

Optimal sensor location for detecting changes in dynamical behavior

Abstract: We address the problem of optimal sensor location for monitoring the eigenstructure of a multivariable dynamical system. The criterions which are optimized are the power of new tests designed for detecting and diagnosing changes in the eigencharacteristics of a system [3], [12]. The key points are the choice of the parameterization for computing the criterion and the comparison of designs with a different number of sensors. The discussion of the numerical results for sensor location includes the analysis of the effect of the geometry of the unknown excitation.

Estimating the multiplicities of conflicts to speed their resolution in multiple access channels

Abstract: New, improved algorithms are proposed for regulating access to a multiple-access channel, a common channel shared by many geographically distributed computing stations. A conflict of multiplicity n occurs when n stations transmit simultaneously to the channel. As a result, all stations receive feedback indicating whether n is 0, 1, or ≥2. If n = 1, the transmission succeeds; whereas if n ≥ 2, all the transmissions fail. Algorithms are presented and analyzed that allow the conflicting stations to compute a stochastic estimate n* of n, cooperatively, at small cost, as a function of the feedback elicited during its execution. An algorithm to resolve a conflict among two or more stations controls the retransmissions of the conflicting stations so that each eventually transmits singly to the channel. Combining one of our estimation algorithms with a tree algorithm (of Capetanakis, Hayes, and Tsybakov and Mikhailov) then leads to a hybrid algorithm for conflict resolution. Several efficient combinations are possible, the most efficient of which resolves conflicts about 20 percent faster on average than any of the comparable algorithms reported to date.

On the semantics of concurrency: partial orders and transition systems

Abstract: We introduce an algebra of labelled event structures whose operations are sequential composition, sum, and parallel composition. A transition relation is defined on these objects, where at each step a process performs a labelled poset. It is claimed that the bisimulation relative to such transition systems brings out a clean distinction between concurrency and sequential non-determinism.

Error diagnosis in logic programming, an adaptation of E.Y. Shapiro's method

Abstract: We study Shapiro's method of bug diagnosis in the theoretical framework of Horn clause logic programming. Within the framework of Clark's semantics (Herbrand's universe with variables, which is more general than the most usual semantics without variables) we extend the scope of fixpoint and declarative semantics of logic programming.

Bounds on the propagation of selection into logic programs

Abstract: We consider the problem of propagating selections (i.e., bindings of variables) into logic programs. In particular, we study the class of binary chain programs and define selection propagation as the task of finding an equivalent program containing only unary derived predicates. We associate a context free grammar L(H) with every binary chain program H. We show that, given H propagating a selection involving some constant is possible iff L(H) is regular, and therefore undecidable. We also show that propagating a selection of the form p(X,X) is possible iff L(H) is finite, and therefore decidable. We demonstrate the connection of these two cases, respectively, with the weak monadic second order theory of one successor and with monadic generalized spectra. We further clarify the analogy between chain programs and languages from the point of view of program equivalence and selection propagation heuristics.

The Representation, Recognition, and Positioning of 3-D Shapes from Range Data

Abstract: The task of recognizing and positioning rigid objects in 3-D space is important for robotics and navigation applications. In this paper we analyze the task requirements in terms of what information needs to be represented, how to represent it, what paradigms can be used to process it and how to implement them.

An optimal region growing algorithm for image segmentation

Abstract: We present a new approach to the segmentation problem by optimizing a criterion which estimates the quality of a segmentation. We use a graph-based description of a partition of an image and a merg...

A translation language complete for database update and specification

Abstract: In the past few years, there has been increased interest m mcludmg dynamic aspects mto database design and speclficatlon [Br,CCF,MBH,V,etc] In particular, recent research focused on the use of transactions as speclficatlon tools (AVZ,AVS,SS] and on the computatlonal power of transactions [AV2,AV4] Results m [AV2] suggest notlons of completeness for transaction languages which are analogs of the notions of completeness for query languages, but are particular to transactions In this paper, we consider several such notlons, and present a simple and natural transaction language (TL) which IS complete with respect to these criteria

The CHORUS Distributed Operating System: Some Design Issues

Abstract: CHORUS ™ is a portable, open, message-based, distributed operating system. Since 1980, start time of the CHORUS project at INRIA, several versions of the system have been designed and implemented. The current version, CHORUS-V2, offers a full UNIX ™ compatibility at the user level, while providing control of distribution by relying on a powerful IPC facility, based on ports and messages, as the heart of its architecture.

An object centered hierarchical representation for 3D objects: the prism tree

Abstract: Efficient computation of surfaces and/or solids intersections is a cornerstone of many algorithms in geometric modelling and computer graphics, for example, set operations between solids, or ray casting display of surfaces. We represent an object centered, information preserving, hierarchical representation for polyhedra called prism tree, establish its fundamental properties, and give a neighbor-finding algorithm. The representation is then used to decompose the intersection algorithms in two steps: the localization of intersections, and their processing. When dealing with polyhedra with many faces (typically more than one thousand), the first step is by far the most expensive. The prism tree structure is used to compute efficiently this localization step. A preliminary implementation of the set operations and ray casting algorithms has been constructed.

Building a consistent 3D representation of a mobile robot environment by combining multiple stereo views

Abstract: In this short article, we report new results on our work on the problem of using passive Vision and more precisely Stereo Vision to build up consistent 3D geometric descriptions of the environment of a mobile robot I-INTRODUCTION The robot that we have built consists of a four-wheeled platform with two driving wheels operated by electrical motors. A set of three CCD cameras provides black and white images of the environment The cameras are located at the vertexes of a vertical roughly equilateral triangle. Images are transmitted via a VHF link to a workstation where they are stored and made available through Ethernet to a number of processors. To the user, the vehicle appears as a standard peripheral and can be accessed as such from any terminal on the net It is therefore a very convenient testbed for studying a number of problems in Vision. One such problem is the following. Suppose we let our vehicle wander around in a building using its ultrasound sensors to avoid obstacles, odometry to roughly estimate its motion and its three cameras to compute 3D descriptions of its environment One question then is, can we hope to combine coherently the various sources of information, and especially the visual information obtained at different times and from different places, and build up an accurate geometric 3D representation of the building even if each individual measurement is itself fairly inaccurate 7 We call this problem the Visual Fusion problem. There are two deep issues which are associated with this question. First is the issue of the type of geometric representation that is used by the system. Representations which are mathematically equivalent may behave quite differently on a real problem due to the unavoidable presence of noise and errors. This brings up the second issue which is the question of how do we represent and manipulate uncertainty. In the next Sections we propose a solution to these issues and present some results. ll-WHAT IS THE PROBLEM THAT WE ARE TRYING TO SOL VE ? Each triplet of images provided by the three cameras is analysed by a Stereo program described in [3,4]. This program outputs 3D line segments described in a coordinate system attached to the three cameras. Each line segment has a geometric description which we elaborate on in the next Section and an uncertainty which we explain in Section IV. This uncertainty is directly related to …

Incremental incrementally compacting garbage collection

Abstract: A mixed-strategy garbage collection algorithm is presented, which combines mark-and-sweep and copy collection. The intent is to benefit from the compacting and linearizing properties of copy collection without losing computational use of half the memory. The stop-and-collect version of the algorithm is a simple and cheap technique to fight memory fragmentation. The collection strategy may be dynamically adapted to minimize the cost of collection, according to the amount of memory actually accessed by the computing process. The parallel version of the algorithm is to our knowledge the only parallel compacting collector for varisized cells, that leaves most (more than half) of the memory available for the computing process.