scholarly journals Epipolar Rectification for CARTOSAT-1 Stereo Images Using SIFT and RANSAC

2014 ◽  
Vol XL-8 ◽  
pp. 1095-1098
Author(s):  
A. Akilan ◽  
D. Sudheer Reddy ◽  
V. Nagasubramanian ◽  
P. V. Radhadevi ◽  
G. Varadan
Keyword(s):  
Image Matching ◽  
Computational Effort ◽  
3D Modelling ◽  
High Fidelity ◽  
Stereo Images ◽  
Generation Algorithm ◽  
One Dimensional ◽  
Processing Step ◽  
Along Track ◽  
Modelling Application

Cartosat-1 provides stereo images of spatial resolution 2.5 m with high fidelity of geometry. Stereo camera on the spacecraft has look angles of +26 degree and -5 degree respectively that yields effective along track stereo. Any DSM generation algorithm can use the stereo images for accurate 3D reconstruction and measurement of ground. Dense match points and pixel-wise matching are prerequisite in DSM generation to capture discontinuities and occlusions for accurate 3D modelling application. Epipolar image matching reduces the computational effort from two dimensional area searches to one dimensional. Thus, epipolar rectification is preferred as a pre-processing step for accurate DSM generation. In this paper we explore a method based on SIFT and RANSAC for epipolar rectification of cartosat-1 stereo images.

scholarly journals A Double Epipolar Resampling Approach to Reliable Conjugate Point Extraction for Accurate Kompsat-3/3A Stereo Data Processing

2020 ◽  
Vol 12 (18) ◽  
pp. 2940
Author(s):  
Jaehong Oh ◽  
Youkyung Han
Keyword(s):  
Image Matching ◽  
Traditional Approach ◽  
Conjugate Point ◽  
Conjugate Points ◽  
Stereo Images ◽  
Matching Methods ◽  
Stereo Data ◽  
Extraction Performance ◽  
Along Track ◽  
Bias Compensation

Kompsat-3/3A provides along-track and across-track stereo data for accurate three-dimensional (3D) topographic mapping. Stereo data preprocessing involves conjugate point extraction and acquisition of ground control points (GCPs), rational polynomial coefficient (RPC) bias compensation, and epipolar image resampling. Applications where absolute positional accuracy is not a top priority do not require GCPs, but require precise conjugate points from stereo images for subsequent RPC bias compensation, i.e., relative orientation. Conjugate points are extracted between the original stereo data using image-matching methods by a proper outlier removal process. Inaccurate matching results and potential outliers produce geometric inconsistency in the stereo data. Hence, the reliability of conjugate point extraction must be improved. For this purpose, we proposed to apply the coarse epipolar resampling using raw RPCs before the conjugate point matching. We expect epipolar images with even inaccurate RPCs to show better stereo similarity than the original images, providing better conjugate point extraction. To this end, we carried out the quantitative analysis of the conjugate point extraction performance by comparing the proposed approach using the coarsely epipolar resampled images to the traditional approach using the original stereo images. We tested along-track Kompsat-3 stereo and across-track Kompsat-3A stereo data with four well-known image-matching methods: phase correlation (PC), mutual information (MI), speeded up robust features (SURF), and Harris detector combined with fast retina keypoint (FREAK) descriptor (i.e., Harris). These matching methods were applied to the original stereo images and coarsely resampled epipolar images, and the conjugate point extraction performance was investigated. Experimental results showed that the coarse epipolar image approach was very helpful for accurate conjugate point extraction, realizing highly accurate RPC refinement and sub-pixel y-parallax through fine epipolar image resampling, which was not achievable through the traditional approach. MI and PC provided the most stable results for both along-track and across-track test data with larger patch sizes of more than 400 pixels.

scholarly journals AN INTEGRATED PHOTOGRAMMETRIC AND PHOTOCLINOMETRIC APPROACH FOR PIXEL-RESOLUTION 3D MODELLING OF LUNAR SURFACE

2018 ◽  
Vol XLII-3 ◽  
pp. 1117-1122
Author(s):  
W. C. Liu ◽  
B. Wu
Keyword(s):  
High Resolution ◽  
Lunar Surface ◽  
Image Matching ◽  
Point Cloud ◽  
3D Modelling ◽  
Conjugate Points ◽  
Stereo Pair ◽  
Pixel Resolution ◽  
Dense Image ◽  
Lunar Reconnaissance Orbiter

High-resolution 3D modelling of lunar surface is important for lunar scientific research and exploration missions. Photogrammetry is known for 3D mapping and modelling from a pair of stereo images based on dense image matching. However dense matching may fail in poorly textured areas and in situations when the image pair has large illumination differences. As a result, the actual achievable spatial resolution of the 3D model from photogrammetry is limited by the performance of dense image matching. On the other hand, photoclinometry (i.e., shape from shading) is characterised by its ability to recover pixel-wise surface shapes based on image intensity and imaging conditions such as illumination and viewing directions. More robust shape reconstruction through photoclinometry can be achieved by incorporating images acquired under different illumination conditions (i.e., photometric stereo). Introducing photoclinometry into photogrammetric processing can therefore effectively increase the achievable resolution of the mapping result while maintaining its overall accuracy. This research presents an integrated photogrammetric and photoclinometric approach for pixel-resolution 3D modelling of the lunar surface. First, photoclinometry is interacted with stereo image matching to create robust and spatially well distributed dense conjugate points. Then, based on the 3D point cloud derived from photogrammetric processing of the dense conjugate points, photoclinometry is further introduced to derive the 3D positions of the unmatched points and to refine the final point cloud. The approach is able to produce one 3D point for each image pixel within the overlapping area of the stereo pair so that to obtain pixel-resolution 3D models. Experiments using the Lunar Reconnaissance Orbiter Camera - Narrow Angle Camera (LROC NAC) images show the superior performances of the approach compared with traditional photogrammetric technique. The results and findings from this research contribute to optimal exploitation of image information for high-resolution 3D modelling of the lunar surface, which is of significance for the advancement of lunar and planetary mapping.

scholarly journals THE DIGITAL O&P WORKSHOP

2021 ◽  
Vol 4 (2) ◽  
Author(s):  
Manuel Opitz ◽  
Peter Fröhlingsdorf
Keyword(s):  
Digital Health ◽  
3D Modelling ◽  
3D Image ◽  
Image Capture ◽  
Call To Action ◽  
Processing Step ◽  
The Impact ◽  
Near Future ◽  
Rapid Transformation ◽  
Health Experts

Digitalisation is the megatrend in healthcare, not only since the pandemic. We are two European digital health experts and industry leaders in the field of orthotics and prosthetics (O&P) and in this article we explored what are the underlying trends driving the adoption of digitalisation for customisation of prosthetics & orthotics. We showed that several trends in 3D image capture (input step), 3D modelling (processing step) and 3D printing (output step) currently converge and thus fuel the rapid transformation of the O&P industry. In short outlooks, we rated the probability and timing of adoption rates across the upcoming couple of years. We furthermore reviewed the impact of boundary conditions set by regulators as well as the reimbursement system. Towards the end of this article, we outlined a digital scenario of the near future by following around an orthotist during her work. We finished with a call-to-action targeting regulators, payors, prosthetists/orthotists, and patients to enable such a desirable future. Article PDF Link: https://jps.library.utoronto.ca/index.php/cpoj/article/view/36349/28332 How To Cite: Opitz M, Fröhlingsdorf P. The digital O&P workshop. Canadian Prosthetics & Orthotics Journal. 2021; Volume 4, Issue 2, No.15. https://doi.org/10.33137/cpoj.v4i2.36349 Corresponding Author: Manuel Opitz, MECURIS GmbH, Lindwurmstraße 11, 80337 München, Germany.E-Mail: [email protected] number: https://orcid.org/0000-0001-6098-1881

Variable Fidelity Modeling in Closed Loop Dynamical Systems

2014 ◽  
Author(s):  
Matthew A. Williams ◽  
Andrew G. Alleyne
Keyword(s):  
Dynamical Systems ◽  
Closed Loop ◽  
System Development ◽  
Computational Cost ◽  
Computational Effort ◽  
High Fidelity ◽  
Vapor Compression System ◽  
Variable Fidelity ◽  
Time Required ◽  
Fidelity Model

In the early stages of control system development, designers often require multiple iterations for purposes of validating control designs in simulation. This has the potential to make high fidelity models undesirable due to increased computational complexity and time required for simulation. As a solution, lower fidelity or simplified models are used for initial designs before controllers are tested on higher fidelity models. In the event that unmodeled dynamics cause the controller to fail when applied on a higher fidelity model, an iterative approach involving designing and validating a controller’s performance may be required. In this paper, a switched-fidelity modeling formulation for closed loop dynamical systems is proposed to reduce computational effort while maintaining elevated accuracy levels of system outputs and control inputs. The effects on computational effort and accuracy are investigated by applying the formulation to a traditional vapor compression system with high and low fidelity models of the evaporator and condenser. This sample case showed the ability of the switched fidelity framework to closely match the outputs and inputs of the high fidelity model while decreasing computational cost by 32% from the high fidelity model. For contrast, the low fidelity model decreases computational cost by 48% relative to the high fidelity model.

High-Fidelity Rendering of Contact With Virtual Objects

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Arash Mohtat ◽  
József Kövecses
Keyword(s):  
Contact Force ◽  
Constitutive Relations ◽  
Sampling Rate ◽  
Smooth Transition ◽  
Virtual Object ◽  
High Fidelity ◽  
Unified Approach ◽  
One Dimensional ◽  
The Core ◽  
The One

When interacting with a virtual object (VO) through a haptic device, it is crucial to feedback a contact force to the human operator (HO) that displays the VO physical properties with high fidelity. The core challenge, here, is to expand the renderable range of these properties, including larger stiffness and smaller inertia, at the available sampling rate. To address this challenge, a framework entitled high-fidelity contact rendering (HFCR) has been developed in this paper. The framework consists of three main strategies: an energy-based rendering of the contact force, smooth transition (ST) between contact modes, and remaining leak dissipation (LD). The essence of these strategies is to make the VO emulate its continuous-time counterpart. This is achieved via physically meaningful modifications in the constitutive relations to suppress artificial energy leaks. The strategies are first developed for the one-dimensional (1D) canonical VO; then, generalization to the multivariable case is discussed. Renderability has been analyzed exploring different stability criteria within a unified approach. This leads to stability charts and identification of renderable range of properties in the presence and absence of the HO. The framework has been validated through simulation and various experiments. Results verify its promising aspects for various scenarios including sustained contact and sudden collision events with or without the HO.

scholarly journals On the Diagnosis of Aortic Dissection with Impedance Cardiography: A Bayesian Feasibility Study Framework with Multi-Fidelity Simulation Data

Proceedings ◽  
2019 ◽  
Vol 33 (1) ◽  
pp. 24 ◽  
Author(s):  
Sascha Ranftl ◽  
Gian Marco Melito ◽  
Vahid Badeli ◽  
Alice Reinbacher-Köstinger ◽  
Katrin Ellermann ◽  
...  
Keyword(s):  
Aortic Dissection ◽  
Impedance Cardiography ◽  
Heart Function ◽  
Imaging Techniques ◽  
Computational Cost ◽  
Circulatory System ◽  
Magnetic Resonance Tomography ◽  
Computational Effort ◽  
High Fidelity ◽  
Regression Problem

Aortic dissection is a cardiovascular disease with a disconcertingly high mortality. When it comes to diagnosis, medical imaging techniques such as Computed Tomography, Magnetic Resonance Tomography or Ultrasound certainly do the job, but also have their shortcomings. Impedance cardiography is a standard method to monitor a patients heart function and circulatory system by injecting electric currents and measuring voltage drops between electrode pairs attached to the human body. If such measurements distinguished healthy from dissected aortas, one could improve clinical procedures. Experiments are quite difficult, and thus we investigate the feasibility with finite element simulations beforehand. In these simulations, we find uncertain input parameters, e.g., the electrical conductivity of blood. Inference on the state of the aorta from impedance measurements defines an inverse problem in which forward uncertainty propagation through the simulation with vanilla Monte Carlo demands a prohibitively large computational effort. To overcome this limitation, we combine two simulations: one simulation with a high fidelity and another simulation with a low fidelity, and low and high computational costs accordingly. We use the inexpensive low-fidelity simulation to learn about the expensive high-fidelity simulation. It all boils down to a regression problem—and reduces total computational cost after all.

Numerical and Analytical Solutions for Two-Dimensional Gas Distribution in Gas-Loaded Heat Pipes

1989 ◽  
Vol 111 (3) ◽  
pp. 598-604 ◽  
Author(s):  
P. F. Peterson ◽  
C. L. Tien
Keyword(s):  
Heat Pipes ◽  
Computational Effort ◽  
Two Dimensional ◽  
Dimensional Model ◽  
Gas Distribution ◽  
Dimensional Solution ◽  
Integral Analysis ◽  
One Dimensional ◽  
Wide Range ◽  
Design Calculations

This work presents a two-dimensional axisymmetric diffusion model for the non-condensable gas distribution in gas-loaded heat pipes and thermosyphons. The new model, based on an integral analysis, has major advantages over existing, computationally time consuming, two-dimensional models. It has equal accuracy while using only the computational effort required for the cruder one-dimensional model, and also includes the effects of wall conduction and spatial variation of the condenser heat transfer coefficient. To simplify design calculations further an analytic two-dimensional solution is established, which gives excellent results over a wide range of parameters.

scholarly journals Impact of the Acquisition Geometry of Very High-Resolution Pléiades Imagery on the Accuracy of Canopy Height Models over Forested Alpine Regions

2018 ◽  
Vol 10 (10) ◽  
pp. 1542 ◽  
Author(s):  
Livia Piermattei ◽  
Mauro Marty ◽  
Wilfried Karel ◽  
Camillo Ressl ◽  
Markus Hollaus ◽  
...  
Keyword(s):  
High Resolution ◽  
Image Matching ◽  
Canopy Height ◽  
Forest Monitoring ◽  
Aerial Image ◽  
Stereo Pair ◽  
Stereo Images ◽  
Mountain Areas ◽  
Surface Models ◽  
The Impact

This work focuses on the accuracy estimation of canopy height models (CHMs) derived from image matching of Pléiades stereo imagery over forested mountain areas. To determine the height above ground and hence canopy height in forest areas, we use normalised digital surface models (nDSMs), computed as the differences between external high-resolution digital terrain models (DTMs) and digital surface models (DSMs) from Pléiades image matching. With the overall goal of testing the operational feasibility of Pléiades images for forest monitoring over mountain areas, two questions guide this work whose answers can help in identifying the optimal acquisition planning to derive CHMs. Specifically, we want to assess (1) the benefit of using tri-stereo images instead of stereo pairs, and (2) the impact of different viewing angles and topography. To answer the first question, we acquired new Pléiades data over a study site in Canton Ticino (Switzerland), and we compare the accuracies of CHMs from Pléiades tri-stereo and from each stereo pair combination. We perform the investigation on different viewing angles over a study area near Ljubljana (Slovenia), where three stereo pairs were acquired at one-day offsets. We focus the analyses on open stable and on tree covered areas. To evaluate the accuracy of Pléiades CHMs, we use CHMs from aerial image matching and airborne laser scanning as reference for the Ticino and Ljubljana study areas, respectively. For the two study areas, the statistics of the nDSMs in stable areas show median values close to the expected value of zero. The smallest standard deviation based on the median of absolute differences (σMAD) was 0.80 m for the forward-backward image pair in Ticino and 0.29 m in Ljubljana for the stereo images with the smallest absolute across-track angle (−5.3°). The differences between the highest accuracy Pléiades CHMs and their reference CHMs show a median of 0.02 m in Ticino with a σMAD of 1.90 m and in Ljubljana a median of 0.32 m with a σMAD of 3.79 m. The discrepancies between these results are most likely attributed to differences in forest structure, particularly tree height, density, and forest gaps. Furthermore, it should be taken into account that temporal vegetational changes between the Pléiades and reference data acquisitions introduce additional, spurious CHM differences. Overall, for narrow forward–backward angle of convergence (12°) and based on the used software and workflow to generate the nDSMs from Pléiades images, the results show that the differences between tri-stereo and stereo matching are rather small in terms of accuracy and completeness of the CHM/nDSMs. Therefore, a small angle of convergence does not constitute a major limiting factor. More relevant is the impact of a large across-track angle (19°), which considerably reduces the quality of Pléiades CHMs/nDSMs.

Gross Error Considered Stereo Images Relative Orientation

2014 ◽  
Vol 687-691 ◽  
pp. 3755-3759
Author(s):  
Hai Qing He ◽  
Xiao Yong Chen
Keyword(s):  
Iterative Algorithm ◽  
Image Matching ◽  
Negative Influence ◽  
Relative Orientation ◽  
Experimental Results ◽  
Stereo Images ◽  
Gross Error ◽  
Novel Approach

Relative orientation is one of the most important and classic tasks in photogrammetry. Gross error of the corresponding points may be caused by computer automatic image matching, the commonly used method is unsuitable to relative orientation. In this paper, a novel approach of stereo images relative orientation considering gross error was proposed. Firstly the initial elements of relative orientation are computed by direct relative orientation, then the refined elements of relative orientation are obtained by Huber and iterative algorithm in the continuous relative orientation, which can eliminate the negative influence of gross error. Experimental results show that the proposed approach can achieve more excellent performances in accuracy than the commonly used method in the corresponding points with gross error.

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