Small Roll Angles Research Articles

Entropy-Based Registration of Point Clouds Using Terrestrial Laser Scanning and Smartphone GPS.

Automatic registration of terrestrial laser scanning point clouds is a crucial but unresolved topic that is of great interest in many domains. This study combines terrestrial laser scanner with a smartphone for the coarse registration of leveled point clouds with small roll and pitch angles and height differences, which is a novel sensor combination mode for terrestrial laser scanning. The approximate distance between two neighboring scan positions is firstly calculated with smartphone GPS coordinates. Then, 2D distribution entropy is used to measure the distribution coherence between the two scans and search for the optimal initial transformation parameters. To this end, we propose a method called Iterative Minimum Entropy (IME) to correct initial transformation parameters based on two criteria: the difference between the average and minimum entropy and the deviation from the minimum entropy to the expected entropy. Finally, the presented method is evaluated using two data sets that contain tens of millions of points from panoramic and non-panoramic, vegetation-dominated and building-dominated cases and can achieve high accuracy and efficiency.

Simplified 7 DOF Model of Car Vertical Vibrations for Small Pitch and Roll Angles

This paper concerns a simplified 7 DOF model for car vertical vibrations. The classical 7 DOF of the considered 3D vertical model are: the vertical displacement of the gravity center of the car body, the roll and pitch angles of the car body and the four vertical displacements of the wheels centers. Using the x-y-z sequence of rotations parameterization, the Euler’s rotation equations concerning the roll and pitch angle are easily obtained. Small differences are observed between our car body rotation equations concerning the two pitch and roll angles and the same equations provided by Demić et al. [6]. For small pitch and roll angles, no differences were observed with respect with [6]. Also, no differences were observed concerning the other 5 dynamics equations of the 7 DOF model, the ones for the vertical displacements.The simplified 7 DOF car vertical dynamics model, comprising two rotation equations (for pitch and roll angles) and five dynamics equations concerning vertical displacements/accelerations, were integrated/simulated in Matlab. For small pitch and roll angles (a rather flat and smooth straight road profile was considered in our case study), the results obtained using the in-house 7 DOF model Matlab simulator are in very good agreement with the results provided by CARSIM.

Note: A small roll angle measurement method with enhanced resolution based on a heterodyne interferometer.

Small roll angle is hard to be measured directly by commercial interferometer instruments due to their low sensitivities in axial direction. A method for its measurement based on a heterodyne interferometer is presented, which adopts accessories including a half wave plate, a multiple-reflector, and a phase meter to achieve test by detecting phase differences between the measurement and reference arms. Mathematical model reveals the resolution will be improved by increasing pass times through the half wave plate. The theoretical resolution is up to 0.19 in. when the pass times increase to three and the phase meter resolution is 0.01°. The proposed method is proved by the experiment.

차선검출 기반 카메라 포즈 추정

Abstract : When a camera installed on a vehicle is used, estimation of the camera pose including tilt, roll, and pan angle with respect to the world coordinate system is important to associate camera coordinates with world coordinates. Previous approaches using huge calibration patterns have the disadvantage that the calibration patterns are costly to make and install. And, previous approaches exploiting multiple vanishing points detected in a single image are not suitable for automotive applications as a scene where multiple vanishing points can be captured by a front camera is hard to find in our daily environment. This paper proposes a camera pose estimation method. It collects multiple images of lane markings while changing the horizontal angle with respect to the markings. One vanishing point, the cross point of the left and right lane marking, is detected in each image, and vanishing line is estimated based on the detected vanishing points. Finally, camera pose is estimated from the vanishing line. The proposed method is based on the fact that planar motion does not change the vanishing line of the plane and the normal vector of the plane can be estimated by the vanishing line. Experiments with large and small tilt and roll angle show that the proposed method outputs accurate estimation results respectively. It is verified by checking the lane markings are up right in the bird’s eye view image when the pan angle is compensated.

AUTOMATIC REGISTRATION OF APPROXIMATELY LEVELED POINT CLOUDS OF URBAN SCENES

Abstract. Registration of point clouds is a necessary step to obtain a complete overview of scanned objects of interest. The majority of the current registration approaches target the general case where a full range of the registration parameters search space is assumed and searched. It is very common in urban objects scanning to have leveled point clouds with small roll and pitch angles and with also a small height differences. For such scenarios the registration search problem can be handled faster to obtain a coarse registration of two point clouds. In this paper, a fully automatic approach is proposed for registration of approximately leveled point clouds. The proposed approach estimates a coarse registration based on three registration parameters and then conducts a fine registration step using iterative closest point approach. The approach has been tested on three data sets of different areas and the achieved registration results validate the significance of the proposed approach.

Preparation of superhydrophobic surfaces on Al substrates and the anti-icing behavior

A low-cost and simple methodology is successfully developed for preparation of superhydrophobic surfaces on Al alloys. By the selection of an optimal concentration of the etching solution, a relatively large contact angle of 160° and a small roll angle small to 4° can be achieved. Such superhydrophobic surfaces also exhibit the remarkable anti-icing characteristics. In particular, the icing time on the surfaces can be delayed considerably. Therefore our study suggests that the present methodology and the prepared superhydrophobic surfaces could be applied in various engineering fields.

Land Vehicle Navigation with the Integration of GPS and Reduced INS: Performance Improvement with Velocity Aiding

The movement of a land vehicle is constrained because the vehicle always remains on the Earth's surface and only experiences small pitch and roll angles. So the GPS/INS integrated system for land vehicle navigation could be reconfigured to be the integration of GPS and reduced INS to cut down the costs. In a reduced INS, the vertical accelerometer and two horizontal gyros could be omitted from the system. But both theoretical analysis and experimental results show that this configuration may result in the divergence of height solution and large velocity errors. To improve the system performances, precise velocity derived from GPS carrier phase measurements, together with the GPS single point positioning solution, is used to aid the reduced INS. Field test results have demonstrated that first, the aiding from GPS precise velocity overcomes the divergence problem of the integrated height solutions and improves the integrated velocity and secondly the proposed novel integration scheme could achieve comparable navigation accuracy with that from the GPS and full INS integrated system.

Synthesis of Superhydrophobic Silicon Oxide Nanowires Surface on Silicon Wafer

High roughness of several hundreds of nanometers and low free energy introduced the superhydrophobic surface with a high water contact angle of approximatelt 160 degrees for the chemically modified silicon oxide nanowires on silicon wafer. Particularly, a very small rolling angle of < 5 degrees with the annealed sample was observed. The nano-structure with high roughness and organic perfluoroalkysilane coating with CF2/CF3 groups contributed the superhydrophobicity. The present superhydrophobic nanowires surface on silicon wafer suggests the potential applications in self-cleaning semiconductor devices such as radar surface, solar cell.

Analysis of sequence dependent variations in secondary and tertiary structure of tRNA molecules.

The double helical regions of the five tRNA(Phe) and two tRNA(Asp) crystal structures have been analyzed using the local basepair step parameters. The sequence dependent effects in the mini double helices of tRNA are very similar to those observed in the crystal structures of oligonucleotides in the A-form, the purine-pyrimidine and purine-purine steps have small roll angles when compared to the fiber models of A-DNA as well as A-RNA, while the pyrimidine-purine doublet steps have large roll angles. The orientation of the basepairs in the D-stem is unusual and invariant i.e. they are different from the other three stems but are very similar in all the five tRNA(Phe) crystal structures, presumably due to tertiary interaction of the Watson-Crick basepairs with other bases, with all bases being highly conserved. The origin of the differences between the tertiary structures of tRNA(Phe) and tRNA(Asp) from yeast has also been investigated. It is found that even though the angle between the acceptor arm and the D-stem is very similar in the two structures, the angle subtended by the acceptor arm and the anticodon arm is smaller in the tRNA(Phe) structure (by more than 10 degrees). This is due to differences in the orientation of the two mini helices constituting the anticodon arm, which are inclined to each other by approximately 25 degrees in tRNA(Phe) and 16 degrees in tRNA(Asp). In addition, the acceptor arm, the D-stem and the anticodon stem are nearly coplanar in tRNA(Phe), while in tRNA(Asp) the anticodon stem projects out of the plane defined by the acceptor arm and the anticodon stem. These two features together lead to a larger separation between the acceptor and anticodon ends in tRNA(Asp) and indicate that the junction between the D-stem and the anticodon stem is quite variable, with features characteristic of a ball-and-socket type joint and determined for each tRNA molecule by the base sequence at the junction.

DNA Polymorphism and Local Variation in Base-Pair Orientation: A Theoretical Rationale

Basepair stacking calculations have been carried out to understand the conformational polymorphism of DNA and its sequence dependence. The recently developed self-consistent parameter set, which is specially suitable for describing irregular DNA structures, has been used to describe the geometry of a basepair doublet. While for basepairs without any propeller, the favourable stacking patterns do not appear to have very strong features, much more noticeable sequence dependent stacking patterns emerge once a propeller is applied to the basepairs. The absolute minima for most sequences occurs for a doublet geometry close to the B-DNA fibre models. Hence in the B-DNA region, no strong sequence dependent features are found, but the range of doublet geometries observed in the crystal structures generally lie within the low energy contours, obtained from stacking energy calculations. The doublet geometry corresponding to the A-DNA fibre model is not energetically favourable for the purine-pyrimidine sequences, which prefer small roll angle values when the slide has a large negative value as in A-DNA. However positive roll with large negative slide is allowed for GG, GA, AG and the pyrimidine-purine steps. This is consistent with the observed geometries of various steps in A-DNA crystals. Thus the general features of the basepair doublets predicted from these theoretical studies agree very well with the results from crystal structure analysis. However, since most sequences show an overall preference for B-type doublet geometry, the B----A transition for random sequence DNA cannot be explained on the basis of basepair stacking interactions.