Table of Content

20 August 2013, Volume 42 Issue 4

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A New Method about Terrain Feature Extraction Based on CDT of Contour Feature Curve

2013, 42(4):  0-0. 

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Terrain Features include terrain feature points and terrain feature lines. They are important medias to analysis and processes of landscape, and the important contents of the structure generalization of landscape. This paper proposes and implements a new method of contour- based terrain features lines extraction. Firstly, the contour lines are divided into two kinds of feature segments that include concave and convex segments, which corresponds to the valleys and ridges respectively , and using the maximum-angle as the constraint condition and using the edges of feature segments as the constraint edges, Constrained Delaunay Triangulation(referred to CDT) are constructed. Then，the skeletons of the CDT of every feature segment are traced and the local terrain structure line tree are constructed based on the obtained skeletons. And the leaf nodes of the terrain structure line trees are extracted and be treated as the terrain feature points of the corresponding feature segment. Finally, these terrain feature points are tracked and connected into terrain structure lines by applying the connecting criterion. Furthermore, this paper conducts the related experiments, which verifies the effectiveness and advantages of the methods proposed by this paper.

Geographic-feature Oriented Ria Coastline Simplification

2013, 42(4):  0-0. 

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Geographic-feature oriented generalization is an active issue in field of map generalization. This study attempts to investigate the question of ria coastline simplification. Based on the analysis of ria coast origin and geographic characteristics, a new method has been developed for ria coastline simplification. Firstly hierarchical estuary tree model is built by Delaunay to represent dendritic pattern of ria coastline. Then minor estuaries is deleted in order to generalize the coastline. The generalization results maintain dendritic pattern of ria coastline, and is self topologically consistent, granted for sail safety.

The Region-based Geometric Correction Model for Remote Sensing Image

2013, 42(4):  0-0. 

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Traditional remote sensing image geometric correction model is based on control points. However, the areal features in images can be easier extracted automatically than the point features in many cases. The definitions and algorithms of the distance between the area features and how to establish the error equation using ground control area are proposed, and geometric correction based on areal features is achieved in this paper. Landsat, ALOS and QuickBird images are used as examples for the test and the experimental results show that the proposed method can be used for different satellite images and imaging models. The calibration accuracies in the test are basically the same, both are less than one pixel, when the control data does not contain gross errors for control area and control point, while the area-based geometric correction model is more fault-tolerant than the point-based model when the control data contains gross errors.

Removing the Effects of Azimuth Ambiguities on Ships Detection Based on Polarimetric SAR Data

2013, 42(4):  0-0. 

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During the SAR imaging process, it usually utilized the Doppler frequency caused by ship targets moving relative to SAR sensor to improve the azimuth resolution by azimuth compression. For ship targets, it often led to the strong intensity azimuth ambiguities due to the discrete sampling of the Doppler frequency signal caused by lower PRF emitted by SAR. Because of the azimuth ambiguities having higher gray value, they always were mistaken as the real ships by directly applying the classical targets detection algorithms, such as CFAR, sub-aperture cross-correlation, etc., thus they reduced accuracy of ships detection. Therefore, in this paper, it proposed a new ships detection algorithm based on polarimetric data, which making use of the third scattering mechanism obtained from the results of the H-A-Alpha polarimetric decomposition, and utilizing the sub-aperture cross-correlation theorem to eliminate the effects of azimuth ambiguities on ships detection, and improve the TCR of ship targets. Moreover, it is indicated that the algorithm can eliminate the azimuth ambiguities efficiently, reduce false alarm rate to improve the accuracy of ship targets detection by using C band JPL AIRSAR polarimetric data from the Kojimawan in Tamano, Japan.

A Method of Road Network Generalization Considering Stroke Properties of Road Object

2013, 42(4):  0-0. 

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In road feature generalization, the selection has to consider the grade in semantic description, the length shape in geometric characteristics, the distribution density and the accessibility in topological properties. The traditional method evaluates the road entity importance taking into account just one aspect, for example the segment length, node joint or mesh density, and then completes the selection process by ordering the importance “qualify”. Due to the lack of effective approach to take into account the spatial distribution information of road network, the method is not able to inherit the original spatial distribution characteristics. This paper presents a new method trying to keep the original spatial distribution characteristics. Firstly, concatenating the road segments into strokes and evaluating the importance of every stroke; secondly, selecting roads by the importance of stroke, but adding two types of constraint conditions to the above process, including class constraint conditions and spatial proximity constraint conditions. This proposed approach considers topological, geometric, semantic and the spatial distribution information of road network, and the experiments show that this method is convincing.

Pattern-based node matching approach for road networks

2013, 42(4):  0-0. 

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This paper presents an approach to match nodes from heterogeneous road networks in the identical urban area. The heterogeneous road networks are often produced at different levels-of-detail (LoD) and coordinate systems, which leads to difficulties for matching and integrating between them. Firstly, dual carriageways and complex road junctions are identified as road patterns to eliminate the LoD effect of different datasets. Then the block patterns around nodes in heterogeneous road networks are extracted to make nodes comparable. The comparison is thereby made between two local networks derived from compared nodes. The original local networks are rotated and scaled according to each possible pattern correspondence, and the optimal one is measured with the maximum similarity value. After the pattern matching, two compared heterogeneous networks are approximately registered into the similar coordinate system, and the remaining nodes will be matched with geometrical and topological methods. An experiment of matching heterogeneous road networks is carried out without any other semantic information. The result shows the approach can get satisfactory nodes matching from heterogeneous road networks.

Adaptive Water Level Correction Algorithm for Flooding Analysis

2013, 42(4):  0-0. 

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Flood loss assessment is the basis of flood control and disaster mitigation decision-making, and the primary tasks in flood assessment are to pinpoint the flooding area, depth of water and duration of flooding based on Digital Elevation Model (DEM). The limited resolution and random error of DEM result in abnormal depressions which embarrass the computation of flow direction. Traditional methods process the depressions in DEM by filling the depressions with the same elevation to create a depression-free surface, which result in new problems like the up-lifting of water level on slopes and flood cut-off in flat area. To overcome these shortcomings, this paper presents an adaptive water level correction algorithm for accurate flooding analysis to derive flooding area, flood depth and duration time. According to the characteristics of floods, the correction value is adaptive to flood rate, flood depth variation and flooding time. Terrains of different types range from flat to hilly to mountainous are selected for testing. Experimental results prove that by means of this method, more accurate and reliable flooding information can be available, which is prior to scientific and prompt flood assessment and decision-making.

High Accuracy Geometric Calibration of ZY-3 Three-Line Image

2013, 42(4):  0-0. 

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High accuracy geometric calibration is a key technology of stereo mapping. In this paper, the sensor model for calibration is proposed, as well as the interior orientation model is established considering the characteristic of multiple linear CCD sensors parallel imaging. On this basis, the geometric model of the method that combines several images of some test fields to perform the calibration is established using the offset matrix and the interior orientation model. In the experiment, several 1:2000 DOM and DEM of different test fields of North China are taken as control data to calibrate the ZY-3 three-line cameras. After applying the proposed method, the positioning accuracy without GCPs of ZY-3 three-line images is better than 20m; while the plane positioning accuracy is better than 0.6m and the height accuracy is better than 0.5m with GCPs. The interior calibration result demonstrates the ZY-3 three-line cameras do not have lens distortion

Multi-way Trees Representation for Curve Bends

2013, 42(4):  0-0. 

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According to the defects of current bend identification methods, this paper proposes a multi-way tree structure for representation of curve bends. The method uses curve axis to identify curve bends. Bends which exist in different direction and different range of curve are extracted hierarchically by a recursive way and a multi-way tree of bends is generated according to extraction results. Finally, the multi-way tree of bends was used in the experiment of line generalization and verified its effectiveness.

Parallel Computing Suitability of Contour Simplification Based in MPI

2013, 42(4):  0-0. 

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In recent years, hardware resources with multicore and parallel architecture are emerging in an endless stream. There is still a relative lack of parallel software because parallel programming is more complicated. With the demands of web mapping and on-demand mapping, the efficiency of map generalization needs to be promoted and the study on map generalization parallel computing is gradually appreciated. This paper compared the parallel computing suitability of the different contour simplification algorithms based on MPI. We first analyzed the efficiency of the simplification algorithms based on the time complexity analysis. We explored the three key points such as data partitioning and consolidating, communication mode and computing process after we constructed the parallel computing process of contour simplification. We selected four typical simplification algorithms and ran the parallel computing experiment using the contour data which the quantity is arithmetic. The experiment result proves that the parallel computing efficiency of the simplification algorithms cannot be constantly promoted with the computing nodes increasing, especially for the high efficiency serial algorithms. The non-blocking communication mode can help to promote the parallel computing efficiency comparing to the blocking communication mode in MPI. The constraints of the simplification algorithms and the distribution characteristics of the spatial data influence the parallel computing efficiency. Analyzing the parallel computing suitability of simplification, time complexity and the constraints of the simplification algorithms, quantity and the distribution characteristic of data and computing environment should be considered. The study bears substantial significance to the development and application of parallel computing in map generalization and geo-computing area.

The Geometrical Model of Sensor Corrected Products for ZY-3 Satellite

2013, 42(4):  0-0. 

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ZY-3, being China’s first civil high-definition survey satellite, has the capability of acquiring ground stereo data via a single imaging process, and can be adopted in the 1:50000 stereomapping and resource survey and monitoring. To get larger width and higher resolution, ZY-3 gets the ground information by multi-CCD mosaicing. However, it brings much inconvenience to users when operators provide them with divided CCD images since each CCD has its own parameters of rigorous sensor model. To facilitate users, we will introduce the generating method of sensor corrected (SC) products based on the distortionless rigorous sensor model of SC products proposed in this paper. SC products successfully solve the problem of CCD mosaicing, ensuring both visual seamlessness and geometrical seamlessness; the problem of registration among multispectral bands and guarantee the high precision at the same time. Since SC products eliminate most distortions, it has extremely high RFM replacement accuracy of rigorous sensor model, which can be less than 1% pixel. In the experiment, we use three-line data of Anping and Dengfeng areas to perform the adjustment with no/4 corner GCPs. When without GCPs, the stereo positioning accuracy of ZY-3 can reach 15 meters; while the plane error is less than 3 meters and altitude error less than 2 meters when with 4 corner GCPs. Moreover, the plane positioning accuracy of three-line data is better than two-line data.

A method of extracting Multiscale skeletons for polygonal shapes

2013, 42(4):  0-0. 

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Polygon skeleton is generally recognized as a good shape descriptor. The multiscale representation of polygon skeletons makes it convenient for image analyzing, such as polygon shape recovering, pattern recognition etc. This paper presented a new method to extract multiscale skeletons basing on double buffering transforming, obstacle distance transforming and Voronoi diagram. We tested our method by extracting various skeletons from polygons in different shapes and compared the skeletons qualities from the following indexes, connectivity, topological consistency, and graphics rotating sensitivity. These experimental polygons include complex lake polygon, simple polygon, polygons with holes and noisy polygons. Result shows that according to the above criteria, our method outperforms existing methods to a certain extent.

A Displacement Field Model to Resolve Multiple Spatial Conflicts

2013, 42(4):  0-0. 

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To settle spatial conflicts by displacement operations, the map generalization algorithms has to take into account the conflicts resulted from different contexts and to retain the spatial patterns and relations among spatial objects. This paper presents a multi-source force field based method to deal with the displacement of polygon cluster considering the aspects above. The distance between neighboring polygons in Voronoi diagram is used to detect spatial conflicts and repulsive forces sources are introduced at the conflict places. In the displacement field the vectorial sum of each forces is computed as the displacement offset distance and direction. In this model, object groups are detected and remained as a whole to retain their spatial patterns and relations. Taking the displacement of building cluster as the example, this study shows that by using this displacement field model the new conflicts were avoided and spatial relationships of buildings were kept.

A Robust SVR Image Fusion Method Based on Local Spectral and Spatial Correlation

2013, 42(4):  0-0. 

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To solve the potential color distortion problem of SVR (Synthetic Variable Ratio) method, an improved fusion method based on local spectral and spatial correlation is proposed. The proposed method uses spectral and spatial correlation characteristics and local optimization strategy to simulate panchromatic image, which can effectively reduce the spectral distortion of fused image. To assess the quality of the proposed method, several satellite images such as WorldView-2 panchromatic and multispectral images were used. Comparing with some existed popular techniques, visual and quantitative analysis proved that the proposed method can significantly improve the fusion quality.

Downward continuation of airborne gravity data based on rectangular harmonic analysis

Yamin Dang

2013, 42(4):  0-0. 

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Rectangular harmonic analysis (RHA) is proposed for the downward continuation (DWC) of airborne gravity data in this paper, the mathematical model and detailed algorithm are presented. By conducting a simulated numerical experiment based on EGM2008 Earth gravitational model, three DWC approaches: RHA, direct method and inverse Poisson integral method based on generalized ridge estimate are compared and studied. The 2.5′×2.5′gravity disturbances with Gauss white noise at the flight levels are downward continued to the Geoid and compared with the true values. The numerical results show that RHA performs better than direct method or inverse Poisson integral method based on generalized ridge estimate.

Geomagnetic Data Frequency Divisive Compression and Reconstruction Based on Compressed Sensing

2013, 42(4):  0-0. 

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It is necessary to compress the geomagnetic data in order to establish the high precision reference database. However, for the practical application of navigation, the details of high frequency which contain the texture or edge feature of the image need to be reserved. Hence, a novel method for geomagnetic data compression and reconstruction was presented. Algorithm is based upon discrete cosine transform for data frequency divisive compression, and takes advantage of compressed sensing for sparse signal recovery. Data are reconstructed from partial cosine transform measurements, as minimizers of the sum of two terms corresponding to total variation and l1-norm of a certain transform. The simulation tests and analysis of actual measured geomagnetic data show that, faithful geomagnetic data can be reconstructed from a subset that represents a mere 25 percent of the complete set of measurements. Comparing with traditional filtered back projection methods, it gives better apparent advantages in reconstruction quality and robustness, and the most increase value of peak signal to noise ratio is 5dB.

Enhancement of Airborne SAR Images without Antenna Direction Map

2013, 42(4):  0-0. 

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In order to reduce the influence of antenna direction map and range to SAR imaging, and to improve the visualization and explanation without antenna direction map, an enhancement algorithm for SAR images with intensity integral in azimuth to calculate factors was proposed. In this algorithm, the intensities in different ranges were integral along azimuth, and the enhancement factors in range were calculated with the integral data to enhance SAR images. It can reduce the influence of antenna direction map and range, and can get SAR images with consistent tone in range. Airborne SAR images were implied in experiments. The satisfying results were got, as validated the proposed algorithm.

A method of SNR estimation and comparison for remote sensing images

2013, 42(4):  0-0. 

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Signal to noise ratio (SNR) of remote sensing images is an important indicator of radiation performance for on-orbit remote sensors. The estimation and comparison of SNR for on-orbit remote sensing images provide an intuitive way to measure the radiation difference between two remote sensors and the degradation of the same sensor during different periods. However, due to the differences in the on-orbit imaging environment, the traditional SNR estimation methods would vary significantly from the ideal results. In this paper, we propose a new algorithm to automatically estimate and compare SNR through the following scheme: image partition, homogeneous blocks detection, and the transformation from digital number (DN) values to apparent radiance. By comparing SNR of remote sensing images obtained during different periods, the experimental results demonstrate that the proposed algorithm can produce more accurate and reliable results.

Research on 3D Diffusion Filtering Method of Intensity Noise for Terrestrial Laser Scanning Point Cloud

2013, 42(4):  0-0. 

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In order to improve the quality of point cloud, and to realize intensity filtering while preserving edges and details, this paper develops a three dimensional diffusion equation of point cloud intensity aiming at the data characteristics of terrestrial laser scanning. The effect of diffusion scale in filtering is deeply analyzed. The signal to noise ratio (SNR) is taken as quantitative evaluation method for filtering quality. Through the statistics of test and comparative test, the diffusion equation proposed in this paper show good results.

The Improved Sidereal Filtering of Time Series Considering Segments’ Similarity in Coseismic Displacement

2013, 42(4):  0-0. 

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Based on the traditional sidereal filtering method, this paper puts forward an improved sidereal filtering method accounting for segments’ similarity, namely before building filtering operator, firstly determine the segments’ similarity of the coordinates time series between earthquake day and before that day or after that day, and then based on the similarity measure index to identify weight of each day for filtering. In this paper, different similarity measure indicators are analyzed, after that the universal image quality index (UIQI) method is recommended as the similarity measure for the improved sidereal filtering. It’s more scientific and reasonable than other similarity measure which considers the correlation coefficient between two series, own mean value and variance as well. The results show that the improved sidereal filtering can effectively improve the single epoch positioning accuracy and reliability, completely overcome the defects of traditional filtering method, is beneficial to batch processing without manual intervention.

Detecting Spheroidal Mode of Earth’s Free Oscillations Excitated by Wenchuan Earthquake Using Superconducting Gravity observations

2013, 42(4):  0-0. 

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Spheroidal modes of Earth’s free oscillation excitated by Wenchuan Ms8.0 Earthquake are detected by superconducting gravity observations of Canberra、Matsushiro、Membach and Metsahovi in may, 2008. Results show that the errors of 0S0 to 0S48、1S4、2S4 and 3S1 are between 0.02‰ and 1.93‰ compared with the PREM model, and their signal-to-noise ratios are all bigger than 3. It is shown that the calculation methods are effective and the calculation results are credible. The spectra splittings of the 0S2、0S3 and 0S4 are observed, and their ratios are 1.09340、0.67430 and 1.07100. It is proved that Earth’s rotation and ellipticity are taken as main reasons of the spectra splittings.