Detecting and Determining the Characteristic Points on the Parametric Surface/Surface Intersection

1995 ◽  
Author(s):  
Xianglin Zeng ◽  
Qifu Wang ◽  
Ji Zhou ◽  
Jun Yu
Keyword(s):  
Characteristic Point ◽  
New Method ◽  
Parametric Surface ◽  
Initial Interval ◽  
Surface Modelling ◽  
Surface Intersection ◽  
Characteristic Points ◽  
Numeric Solution ◽  
Modelling System ◽  
Significant Point

Abstract In this paper we present a new method for detecting and determining characteristic points on the surface/surface intersection while marching along the intersections. The initial interval which contains a potential characteristic point is first determined by certain criteria, then a numeric solution of the significant point is obtained by the binary subdivision method. Based on these ideas, a new marching algorithm is constructed, and it has been implemented in a surface modelling system (SurfCADM V1.0). Examples are also presented for illustrating the capability of our algorithm.

scholarly journals An Approach to Computing Multipoint Inversion and Multiray Surface Intersection on Parametric Surface

2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Pei Jingyu ◽  
Wang Xiaoping ◽  
Zhang Leen
Keyword(s):  
High Speed ◽  
Initial Point ◽  
Iteration Process ◽  
Newton Iteration ◽  
Research Field ◽  
New Method ◽  
Parametric Surface ◽  
Surface Intersection ◽  
Arbitrary Precision ◽  
Main Ideas

This article presents a method for multipoint inversion and multiray surface intersection problem on the parametric surface. By combining tracing along the surface and classical Newton iteration, it can solve point inversion and ray-surface intersection issues concerning a large number of points or rays in a stable and high-speed way. What is more, the computation result can approximate to exact solutions with arbitrary precision because of the self-correction of Newton-Raphson iteration. The main ideas are adopting a scheme tracing along the surface to obtain a good initial point, which is close to the desired point with any prescribed precision, and conducting Newton iteration process with the point as a start point to compute desired parameters. The new method enhances greatly iterative convergence rate compared with traditional Newton’s iteration related methods. In addition, it has a better performance than traditional methods, especially in dealing with multipoint inversion and multiray surface intersection problems. The result shows that the new method is superior to them in both speed and stability and can be widely applied to industrial and research field related to CAD and CG.

The Invention and Application of Typical Points-Based Well Log Correlation and Picking Up Technology

2021 ◽  
Author(s):  
Ya Deng ◽  
Yong Li ◽  
Wenqi Zhang ◽  
Dandan Hu ◽  
Zhongyuan Tian ◽  
...  
Keyword(s):  
Characteristic Point ◽  
Free Water ◽  
Water Levels ◽  
New Method ◽  
Quality Analysis ◽  
Stratigraphic Correlation ◽  
Well Log ◽  
Data Set ◽  
Characteristic Points ◽  
Dynamic Performance Analysis

Abstract This paper proposes a new method called typical points-based well log correlation and picking up technology and provides several related application examples based on this method. The new method firstly determines representative extreme points, typical or characteristic points by analyzing the characteristics of logging curves and lithology of different wells, which are generally representative points with special geological significance, including the points with the best physical properties or tight points. (For example, the maximum flooding surface or exposed surface in a sedimentary cycle, etc.). On the basis of these characteristic points, we carry out stratigraphic correlation and tracking between wells to obtain a data set of a series of characteristic points. From the same characteristic point, all points have the same or similar petrophysical properties, and the logging curve values of these characteristic points are extracted. And then analyze the change trend, distribution characteristics and the internal relationship of the parameters of the data set of each feature point. Based on the data set obtained from the method above, we extended it to the following application areas: 1) Through mathematical theoretical models, two free water level distribution modes and their determination workflows were established, including horizontal and tilted free water levels. 2) Perform data quality analysis and control, especially logging data analysis. 3) Exploratory application in the standardization of logging curves.4) Application in dynamic performance analysis The new method is developed on the traditional stratigraphic correlation method and stratal slicing method (Zeng Hongliu, 1998) and then used for well log data extraction and analysis. It is a practical means and technique for geological analysis. The application effect shows that the it is reliable, convenient and practical.

scholarly journals Parametric Surface Modelling for Tea Leaf Point Cloud Based on Non-Uniform Rational Basis Spline Technique

Sensors ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 1304
Author(s):  
Wenchao Wu ◽  
Yongguang Hu ◽  
Yongzong Lu
Keyword(s):  
Point Cloud ◽  
Principal Component ◽  
Point Clouds ◽  
Parametric Surface ◽  
B Spline ◽  
Surface Modelling ◽  
Modelling Method ◽  
3D Architecture ◽  
Tea Leaf ◽  
Fitting Error

Plant leaf 3D architecture changes during growth and shows sensitive response to environmental stresses. In recent years, acquisition and segmentation methods of leaf point cloud developed rapidly, but 3D modelling leaf point clouds has not gained much attention. In this study, a parametric surface modelling method was proposed for accurately fitting tea leaf point cloud. Firstly, principal component analysis was utilized to adjust posture and position of the point cloud. Then, the point cloud was sliced into multiple sections, and some sections were selected to generate a point set to be fitted (PSF). Finally, the PSF was fitted into non-uniform rational B-spline (NURBS) surface. Two methods were developed to generate the ordered PSF and the unordered PSF, respectively. The PSF was firstly fitted as B-spline surface and then was transformed to NURBS form by minimizing fitting error, which was solved by particle swarm optimization (PSO). The fitting error was specified as weighted sum of the root-mean-square error (RMSE) and the maximum value (MV) of Euclidean distances between fitted surface and a subset of the point cloud. The results showed that the proposed modelling method could be used even if the point cloud is largely simplified (RMSE < 1 mm, MV < 2 mm, without performing PSO). Future studies will model wider range of leaves as well as incomplete point cloud.

scholarly journals Blue as an Underrated Alternative to Green: Photoplethysmographic Heartbeat Intervals Estimation under Two Temperature Conditions

Sensors ◽  
2021 ◽  
Vol 21 (12) ◽  
pp. 4241
Author(s):  
Evgeniia Shchelkanova ◽  
Liia Shchapova ◽  
Alexander Shchelkanov ◽  
Tomohiro Shibata
Keyword(s):  
Blue Light ◽  
Characteristic Point ◽  
Biological Effects ◽  
Green Light ◽  
Estimation Accuracy ◽  
Lower Sensitivity ◽  
Light Spectrum ◽  
Cardiovascular Parameter ◽  
Temperature Conditions ◽  
Characteristic Points

Since photoplethysmography (PPG) sensors are usually placed on open skin areas, temperature interference can be an issue. Currently, green light is the most widely used in the reflectance PPG for its relatively low artifact susceptibility. However, it has been known that hemoglobin absorption peaks at the blue part of the spectrum. Despite this fact, blue light has received little attention in the PPG field. Blue wavelengths are commonly used in phototherapy. Combining blue light-based treatments with simultaneous blue PPG acquisition could be potentially used in patients monitoring and studying the biological effects of light. Previous studies examining the PPG in blue light compared to other wavelengths employed photodetectors with inherently lower sensitivity to blue, thereby biasing the results. The present study assessed the accuracy of heartbeat intervals (HBIs) estimation from blue and green PPG signals, acquired under baseline and cold temperature conditions. Our PPG system is based on TCS3472 Color Sensor with equal sensitivity to both parts of the light spectrum to ensure unbiased comparison. The accuracy of the HBIs estimates, calculated with five characteristic points (PPG systolic peak, maximum of the first PPG derivative, maximum of the second PPG derivative, minimum of the second PPG derivative, and intersecting tangents) on both PPG signal types, was evaluated based on the electrocardiographic values. The statistical analyses demonstrated that in all cases, the HBIs estimation accuracy of blue PPG was nearly equivalent to the G PPG irrespective of the characteristic point and measurement condition. Therefore, blue PPG can be used for cardiovascular parameter acquisition. This paper is an extension of work originally presented at the 42nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society.

Subharmonic Coordination in Networks of Neurons with Slow Conductances

1994 ◽  
Vol 6 (1) ◽  
pp. 69-84 ◽  
Author(s):  
Thomas LoFaro ◽  
Nancy Kopell ◽  
Eve Marder ◽  
Scott L. Hooper
Keyword(s):  
Coupled Oscillators ◽  
Characteristic Point ◽  
Reciprocal Inhibition ◽  
Excitable Cell ◽  
Characteristic Points ◽  
Cell Firing ◽  
Voltage Activation ◽  
Phase Relationships ◽  
Excitable Neuron ◽  
Phase Differences

We study the properties of a network consisting of two model neurons that are coupled by reciprocal inhibition. The study was motivated by data from a pair of cells in the crustacean stomatogastric ganglion. One of the model neurons is an endogenous burster; the other is excitable but not bursting in the absence of phasic input. We show that the presence of a hyperpolarization activated inward current (ih) in the excitable neuron allows these neurons to fire in integer subharmonics, with the excitable cell firing once for every N ≥ 1 bursts of the oscillator. The value of N depends on the amount of hyperpolarizing current injected into the excitable cell as well as the voltage activation curve of ih. For a fast synapse, these parameter changes do not affect the characteristic point in the oscillator cycle at which the excitable cell bursts; for slower synapses, such a relationship is maintained within small windows for each N. The network behavior in the current work contrasts with the activity of a pair of coupled oscillators for which the interaction is through phase differences; in the latter case, subharmonics exist if the uncoupled oscillators have near integral frequency relationships, but the phase relationships of the oscillators in general change significantly with parameters. The mechanism of this paper provides a potential means of coordinating subnetworks acting on different time scales but maintaining fixed relationships between characteristic points of the cycles.

Stereo Matching Algorithm Based on Detecting Feature Points

2012 ◽  
Vol 433-440 ◽  
pp. 6190-6194
Author(s):  
Shuo Bo Xu ◽  
Di Shi Xu ◽  
Hua Fang
Keyword(s):  
Stereo Matching ◽  
Characteristic Point ◽  
Feature Points ◽  
Epipolar Line ◽  
Matching Problem ◽  
Matching Algorithm ◽  
Characteristic Points ◽  
Left And Right ◽  
Straight Lines ◽  
Verification Strategy

A new method for solving the stereo matching problem in the presence of large occlusion is presented. This method for stereo matching and occlusion detection is based on searching disparity point. In this paper, we suppose that a pair of epipolar-line images is a projection of a group of piece-wise straight lines on the left and right images respective. Therefore the disparity curve corresponding to a pair of epipolar-line images may be approximated by a group of piece-wise straight lines. Then the key of solving disparity curve is how to get the “characteristic points” on the group of piece-wise straight lines. Based on this view, we fetched out the conception “disparity point”, and three kinds of special disparity points are correctly corresponding to the “characteristic point”. By analyzing intensity property of a disparity point and its neighbor points, an approach which combines stepwise hypothesis-verification strategy with three constraint conditions is devised to extract the candidate disparity points from the epipolar images.

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