Showing papers on "Centroid published in 1983"

Precision of Digital Vision Systems

Abstract: The precision of geometric features such as the centroid, area, perimeter, and orientation measured by a 2-D digital vision system is analyzed and tested experimentally. The digitizing error of various geometric features can be expressed in terms of the dimensionless perimeter of the object. As a result of this work, the sampling process can be simplified or eliminated. The analysis is also expanded to cover the 3-D digital vision systems.

Contour registration by shape-specific points for shape matching

Abstract: The paper shows how registration of planar figures can be achieved using shape-specific points computed from the given figures. Registration makes the subsequent task of shape matching much easier. Examples are given, using the centroid and radius weighted mean, which yield reasonable results even for noisy images.

A normalized quadtree representation

Abstract: The quadtree is a hierarchical data structure used for the compact representation of two-dimensional images. It has the advantages of data compression and fast execution of certain feature computations. However, the quadtree representation of an object is heavily affected by its location, orientation, and relative size. If the image of an object is normalized with respect to its centroid and principal axes, and scaled to a standard size, then its quadtree representation is invariant to rotation, translation, and size change. In addition, the principal moments of objects can be computed from this normalized quadtree representation. These features make it an information-preserving shape descriptor and suitable for tasks such as object recognition.

Small-object location utilizing centroid accumulation

Abstract: In the disclosed image-analysis scheme, a processing window of M by N pixels is successively scanned in single-pixel steps over a sensed image, with the centroid of the image data contained in each window position then being determined. When a pixel-by-pixel tabulation is made of the number of times each pixel has been determined to be the windowed-data centroid, those pixels having the higher tabulated centroid counts will tend to be the intra-image locations of any objects which are smaller than about M/2 by N/2 pixels.

Calculating Centroids in Constrained Mixture Experiments

Abstract: In constrained mixture experiments the centroid of a constraint region has traditionally been defined as the average of all extreme vertices of the region. This differs from the classical physics definition of a centroid as the center of mass (or volume) of a region. An algorithm for calculating a centroid based on the center of mass definition is discussed and illustrated with an example. This centroid calculation technique can be used to calculate centroids of various dimensional faces and edges of the constraint region as well as of the overall centroid. Results of the center-of-mass and averaged-extreme-vertices centroid computation techniques are compared using examples from the literature.

New Centroid Algorithm Based upon Amplitude-Angle Signature

Abstract: A method of estimating the centroid location of a target utilizing radar scan return amplitude versus angle information is presented. The method is compared with three thresholding estimators and a first moment estimator in a computer-simulated automatic landing system. This new method is the most robust and accurate during periods of low signal-to-noise ratio. In periods of high signal-to-noise ratio the method has less error than the thresholding methods and is similar in accuracy to the first moment estimator. Furthermore, the number of pulse transmissions required to obtain a desired level of performance in noise is much less than that needed for the thresholding methods and the first moment estimator employed in this simulation.

A Class of Local Centroid Algorithms for Classification and Quantization in Spaces of Arbitrary Dimension

Abstract: A Class of Local Centroid Algorithms for Classification and Quantization in Spaces of Arbitrary Dimension

Pointing and tracking of particle beams

Abstract: : A problem is considered to determine the feasibility of using a Multiple Model Adaptive Estimator (MMAE) based on space-time point process observations, as part of a control loop The estimator tracks the centroid of a one-dimensional Gaussian-shaped source of individual photo-electron events The centroid is assumed to move dynamically as a first order Guass-Markov process Estimator performance for two implementations (using 'best half' versus 'merge' rationale for limiting the number of individual filters in the MMAE structure) is described in terms of steady-state root mean square error evaluated as a function of six important system parameters Estimates of the beam centroid are used by a regulator based on a Linear system and Quadratic cost criteria to determine the effectiveness of the method For tracking purposes, a real-world target and a Kalman filter are provided based on a first order Guass-Markov process model, and the controller is tested in this environment Results indicate that the estimator provides a viable means of controlling the position of the centroid (Author)

Measuring device for automatically determining the spatial position of body centroids in a three-dimensional mode of representation

Abstract: The invention relates to a measuring device for automatically determining the position of body centroids in a three-dimensional mode of representation, in particular for components. The object of the measuring device consists in automatically determining the position of body centroids, that is to say the aim is to determine all three geometrically possible centroid distances X, Y, Z without additional computation. The object of the measuring device also consists in replacing the previously customary time-consuming computational methods, in which the determination of the body centroid position is conducted over a multiplicity of individual centroids. The object is achieved when the measuring device is used to measure at specific points, by means of measured-value transmitters, reactive forces which are produced by the body weight forces, their control pulses being input into a computer. A visual display unit connected to the computer output, or a printer or plotter connected there, enable visualisation of the three centroid distances sought for the X, Y and Z planes in a three-dimensional mode of representation.

Performance Analysis And Size Optimization Of Focal Planes For Point Source Tracking Algorithm Applications

Abstract: A number of applications require the precise tracking or position estimation of an object that is unresolved in the system optics. This paper evaluates the performance of several interpolation algorithms designed to make these estimates to subpixel accuracy. The tracking sensor examined was a scanning linear array of infrared detectors which were assumed to be background limited. The optics blur spot was assumed gaussian. The relative change in performance with changes in the array configuration was investigated. The detector size and physical spacing were varied parametrically, but with realistic fabrication constraints, to obtain the optimum configuration. The sources of error considered to affect the performance were the systematic algorithm bias, the random noise, and the post-calibration residual detector responsivity nonuniform-ities. The systematic algorithm error or bias was calculated and its rms value over an array pitch was used as one measure of estimation error. The random noise in the signal was propagated by variance analysis into another source of estimation error. Finally, the residual nonuniformities in the detector responsivities after calibration were propagated by variance analysis into an rms spread in the algorithm error, and provide a third source of error. The interpolation algorithms investigated were the odd N point centroids (N = 3, 5, 7, 9) and the three and five-point quadratic curve fits. A simple coarse search routine of peak signal detection was assumed to determine the origin. The optimum performance of a two-row staggered linear array with square detectors and realistic fabrication constraints (P ≥ L/2) occurs for detector lengths (L) slightly less than 1/3 the blur spot size, as defined by 2.44 λ/D where A is the spectral wavelength and D is the optics aperture. The 3 point centroid performs best as a function of signal-to-noise (SNR), but requires a systematic correction of the algorithm bias. The higher N-point centroids quickly degraded in SNR performance but had negligible algorithm error. The quadratic curve fits were worse in SNR performance than the three-point centroid (except for larger, nonoptimized detector sizes) and still required a correction algorithm. The analysis was confirmed with Monte Carlo simulations. An experimental infrared tracking focal plane was purchased and used in a tracker simulation. The tracker error data, taken as a function of SNR confirmed closely the analysis for all signal-to-noise ratios above four. The track error follows the predicted SNR-1 behavior until limited at high SNR to a constant that corresponds to the algorithm bias error in the absence of correction or to the nonuniformity error if a correction routine is included. With the three point algorithms, an experimental accuracy to smaller than 1/100th a detector (<1/250th a blur spot) was obtained at high signal-to-noise ratios.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Image Tracking With Coherent Infrared Radars

Abstract: The image tracking performance of a coherent infrared radar is presented. Heuristic derivations are presented for the tracking accuracy versus image signal-to-noise ratio of centroid, balanced gate, correlation, and template correlation trackers. Expressions for the image signal-to-noise ratio versus carrier-to-noise ratio are obtained for intensity images, thresholded intensity images, range images, and velocity images. Centroid trackers using any type of imagery are shown to yield tracking accuracies which degrade as the target gets larger and are therefore inferior to the other correlation-type trackers. Balanced gate, correlation, and template correlation trackers can all provide tracking accuracies much finer than a pixel. Thresholded intensity, range, and velocity images provide better tracking performance than simple intensity images.

On-line character recognizing device

Abstract: PURPOSE: To decrease a memory quantity of a standard pattern by constituting so that the centroid and a dispersion of a pattern of an input charcter are compared with the centroid and a dispersion of a pattern of a standard charactered prepared in advance. CONSTITUTION: Information of a charcter pictured on a tablet 1 is normalized to a suitable size by a pre-processing device 2. Thereafter, the centroid gravity and a dispersion of each stroke are calculated by a calculating device 3. Subsequently, the centroid and a dispersion of an input character, and the centroid and a dispersion of a standard character stored in advance in a standard pattern accumulating device 5 are compared by a comparing and arithmetic device 4. This comparison is repeated by the number of categories of the standard pattern, the pattern in which a difference between the centroid and a dispersion of the input character and the centroid and a dispersion of the standard character is small is left successively, and in the end, a category to which the pattern in which said difference is the smallest is detected. This category is outputted to the outside by a recognition result output device 6. COPYRIGHT: (C)1985,JPO&Japio

Measuring device of position for light source

Abstract: PURPOSE:To measure exactly and easily the position of a light source by such constitution wherein the image of the light source is formed through a pinhole on a plate sensor, the coordinates of the center of the light source are calculated and the deviation in the geometrical position of the centroid owing to the movement of the light source is calculated CONSTITUTION:The image of the light of a linear light source having covers 221, 222 at both ends within solid lines 251, 252 is formed on a plate sensor (CCD, etc) 13 provided so as to face to a pinhole 11 in a lens barrel A sensor part 10 is so supported that the axis of the part 10 is located at the center 24 of the linear light source 21 in this stage, and the light source 21 is rotated around the centroid of the light source 21 on a horizontal plane The signal of the sensor 41 is inputted through an AD converter 42 to a calculator 42 for the centroid position, by which the rotating speed of the light source 21 is determined and is stored with a rotation discriminator 44 in a tracking device 45 for the movement of the centroid The geometrical center of the centroid of the light source is determined by a calculator 46 for the center of movement, and the eccentricity is determined by a calculator 47 for eccentricity and the results are displayed 50 The position of the light source is thus exactly and easily determined