校准三维模型基矩阵的函数映射的对应关系计算

在利用函数映射计算模型间对应关系时,提出了一种校准三维几何模型之间基矩阵的新方法,将模型间对应关系的构建转化为由模型特征函数构建的基矩阵之间的校准运算。首先计算三维模型的Laplace算子,获得模型的特征值和特征向量,并利用所得到的特征向量构建基矩阵;其次,提出了协方差的最小值校准算法,以计算模型基矩阵之间的校准矩阵 S ,并用矩阵 S 对两个模型的函数基进行校准;最后,计算校准模型所有点的高斯曲率来采样源模型尖端特征点,并在校准后的目标模型上遍历所有点,以寻求最优对应点来构建等距变换（或近似等距变换）的三维模型间的对应关系。通过计算采样点与最优对应点的测地错误,以衡量所提算法的匹配准确率。实验结果表明,与已有算法相比,本算法可以较为准确地构建两个或多个模型间的对应关系,同时也克服了模型自身对称性影响对应关系计算的问题。     

一种基于激光测距仪的扫描匹配方法

扫描匹配是移动机器人定位和环境构图的关键问题之一,通过计算使相邻扫描重叠度最大的最优变换,从而估算相邻时刻的运动量。ICP算法是目前应用最广泛的扫描匹配算法,针对其对离群扫描点和稀疏扫描点敏感的问题,文中提出一种基于连通格序列的方法对扫描数据进行预处理,从而为扫描匹配提供较为理想的输入条件。此外,针对对应关系中一对多和对应距离极端大的问题,文中通过建立唯一对应,并基于四分位数法计算对应距离的上截断点进行剔除,从而避免建立一对多对应,并减少距离极端大的对应。实验结果表明,文中方法能够剔除扫描中的离群点与稀疏点,并改善ICP算法在实际应用中的扫描匹配表现。     

一种机载LiDAR条带平差最小二乘匹配算法

基于七参数正形变换的数据驱动模型实现了机载LiDAR条带平差,算法借鉴了Robert(2004)的最小二乘表面匹 配思想,通过引入高斯–马尔科夫模型改进了原有算法,得到未知参数的最小无偏方差估计。实验采用两组实测数 据,分别考察了引入高斯–马尔科夫模型的必要性、算法效率以及迭代收敛性和算法精度。实验表明：(1)剖面检查吻 合且精度一致;(2)TerraMatch量测匹配精度,理想数据高程匹配误差小于0.05 m,数据质量不理想时误差稍大,但均 能成功匹配。     

Line-based modified iterated Hough transform for automatic registration of multi-source imagery

Image registration aims at combining imagery from multiple sensors to achieve higher accuracy and derive more information than that obtained from a single sensor. The enormous increase in the volume of remotely sensed data that is being acquired by an ever-growing number of earth observation satellites mandates the development of accurate, robust, and automated registration procedures. An effective automatic image registration has to deal with four issues: registration primitives, transformation function, similarity measure, and matching strategy. This paper introduces a new approach for automatic image registration using linear features as the registration primitives. Linear features have been chosen because they can be reliably extracted from imagery with significantly different geometric and radiometric properties. The modified iterated Hough transform (MIHT), which manipulates the registration primitives and similarity measure, is used as the matching strategy for automatically deriving an estimate of the parameters involved in the transformation function as well as the correspondence between conjugate primitives. The MIHT procedure follows an optimal sequence for parameter estimation that takes into account the contribution of linear features with different orientations at various locations within the imagery towards the estimation of the transformation parameters in question. Experimental results using real data proved the feasibility and robustness of the suggested approach.     

3维最小二乘表面匹配泛型数学模型及在机载LiDAR条带平差中的应用

以3维表面间共轭点欧氏距离之和最小为理论基础,提出一种泛型3维表面匹配数学模型,并推导其最小二乘平差理论模型,利用该模型进行机载LiDAR点云条带平差。针对真实机载LiDAR点云数据进行条带平差对比实验,结果表明本文所提出的表面匹配模型,不仅能准确估计出相邻重叠3维表面间的正形变换参数,较好地解决机载LiDAR点云条带间配准问题,而且能同时适用于多种同名点对应准则,是一种泛型的配准模型。     

Complex correspondences in straight line stereo matching

Partial occlusion and fragmented lines will result in the various cases of straight line correspondences, such as one-to-one, one-to-many or many-to-many ones. However, the complex correspondences, such as one-to-many and many-to-many ones, are usually ignored or cannot be established completely in the existing methods. Here, the essence of the complex correspondences will be analyzed. Based on the two characteristics of a straight line, which are introduced by regarding a straight line as a set of collinear points, the compatibility between the complex correspondences and the uniqueness constraint of point correspondence is proved and a new uniqueness constraint of correspondence for matching lines is proposed. Based on the analysis of the complex correspondences, a new concept of line feature group is defined to describe a set of integral correspondences among straight line features from different images and then a new algorithm for establishing all the correspondences completely is described simply. The experimental results with real stereo images illustrate that the complex correspondences among straight lines are actual cases and can be established effectively.     

基于SIFT的宽基线立体影像密集匹配

提出基于对极几何和单应映射双重约束及SIFT特征的宽基线立体影像多阶段准密集匹配算法。算法包括三个阶段：①基于特征点的空间分布和信息熵选取一定数量的最优SIFT特征点集并进行最小二乘初始稀疏匹配及立体像对的基本矩阵和单应矩阵估计;②对于其余特征,利用同名核线倾斜角及SIFT特征的尺度信息对匹配窗口的仿射变换参数进行迭代优化及变形改正、提取仿射不变SIFT特征描述符,并基于双重约束信息及欧氏距离测度进行匹配;③考虑宽基线立体影像较低的特征提取重复率,对第②步左右影像中未能成功匹配的特征点,基于双向搜索策略,采用基于盒滤波加速计算的SSD测度在变形改正后的双重约束区域中进行匹配,并对匹配结果进行加权最小二乘拟合定位。实际的宽基线立体影像试验结果证明了算法的有效性,可为后续的三维重建提供较为可靠的密集或准密集匹配点。     

一种改进SURF的视觉影像匹配算法

视觉影像经常存在纹理情况复杂和动态模糊等情况,严重降低了连续影像间各类特征的相似性,导致传统的匹配算法难以获得准确、稳定、分布良好的影像匹配,影响后续影像处理中各类信息的获取.针对上述情况,本文提出了一种改进SURF视觉影像匹配方法.该方法包括特征提取、初始匹配和对应匹配3个步骤.首先,利用SURF特征匹配方法提取足够...     

Three-image matching. For 3-D linear object tracking

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Three-image matching. For 3-D linear object tracking

This paper will discuss strategies for trinocular image rectification and matching for linear object tracking. It is well known that a pair of stereo images generates two epipolar images. Three overlapped images can yield six epipolar images in situations where any two are required to be rectified for the purpose of image matching. In this case, the search for feature correspondences is computationally intensive and matching complexity increases. A special epipolar image rectification for three stereo images, which simplifies the image matching process, is therefore proposed. This method generates only three rectified images, with the result that the search for matching features becomes more straightforward. With the three rectified images, a particular line-segment-based correspondence strategy is suggested. The primary characteristics of the feature correspondence strategy include application of specific epipolar geometric constraints and reference to three-ray triangulation residuals in object space.     

Accurate 3D comparison of complex topography with terrestrial laser scanner: Application to the Rangitikei canyon (N-Z)

Surveying techniques such as terrestrial laser scanner have recently been used to measure surface changes via 3D point cloud (PC) comparison. Two types of approaches have been pursued: 3D tracking of homologous parts of the surface to compute a displacement field, and distance calculation between two point clouds when homologous parts cannot be defined. This study deals with the second approach, typical of natural surfaces altered by erosion, sedimentation or vegetation between surveys. Current comparison methods are based on a closest point distance or require at least one of the PC to be meshed with severe limitations when surfaces present roughness elements at all scales. To solve these issues, we introduce a new algorithm performing a direct comparison of point clouds in 3D. The method has two steps: (1) surface normal estimation and orientation in 3D at a scale consistent with the local surface roughness; (2) measurement of the mean surface change along the normal direction with explicit calculation of a local confidence interval. Comparison with existing methods demonstrates the higher accuracy of our approach, as well as an easier workflow due to the absence of surface meshing or Digital Elevation Model (DEM) generation. Application of the method in a rapidly eroding, meandering bedrock river (Rangitikei River canyon) illustrates its ability to handle 3D differences in complex situations (flat and vertical surfaces on the same scene), to reduce uncertainty related to point cloud roughness by local averaging and to generate 3D maps of uncertainty levels. We also demonstrate that for high precision survey scanners, the total error budget on change detection is dominated by the point clouds registration error and the surface roughness. Combined with mm-range local georeferencing of the point clouds, levels of detection down to 6 mm (defined at 95% confidence) can be routinely attained in situ over ranges of 50 m. We provide evidence for the self-affine behaviour of different surfaces. We show how this impacts the calculation of normal vectors and demonstrate the scaling behaviour of the level of change detection. The algorithm has been implemented in a freely available open source software package. It operates in complex 3D cases and can also be used as a simpler and more robust alternative to DEM differencing for the 2D cases.     

Automated registration of dense terrestrial laser-scanning point clouds using curves

This paper proposes an automatic method for registering terrestrial laser scans in terms of robustness and accuracy. The proposed method uses spatial curves as matching primitives to overcome the limitations of registration methods based on points, lines, or patches as primitives. These methods often have difficulty finding correspondences between the scanned point clouds of freeform surfaces (e.g., statues, cultural heritage). The proposed method first clusters visually prominent points selected according to their associated geometric curvatures to extract crest lines which describe the shape characteristics of point clouds. Second, a deformation energy model is proposed to measure the shape similarity of these crest lines to select the correct matching-curve pairs. Based on these pairs, good initial orientation parameters can be obtained, resulting in fine registration. Experiments were undertaken to evaluate the robustness and accuracy of the proposed method, demonstrating a reliable and stable solution for accurately registering complex scenes without good initial alignment.     

DEM matching for bias compensation of rigorous pushbroom sensor models

DEM matching is a technique to match two surfaces or two DEMs, at different reference frames. It was originally proposed to replace the need of ground control points for absolute orientation of perspective images. This paper examines DEM matching for precise mapping of pushbroom images without ground control points. We proved that DEM matching based on 3D similarity transformation can be used when model errors are only on the platform’s position and attitude biases. We also proposed how to estimate bias errors and how to update rigorous pushbroom sensor models from DEM matching results. We used a SPOT-5 stereo pair at ground sampling distance of 2.5 m and a reference DEM dataset at grid spacing of 30 m and showed that rigorous pushbroom models with accuracy better than twice of the ground sampling distance both in image and object space have been achieved through DEM matching. We showed further that DEM matching based on 3D similarity transformation may not work for pushbroom images with drift or drift rate errors. We discussed the effects of DEM outliers on DEM matching and automated removal of outliers. The major contribution of this paper is that we validate DEM matching, theoretically and experimentally, for estimating position and attitude biases and for establishing rigorous sensor models for pushbroom images.     

遥感数据时空尺度对地理要素时空变化分析的影响

地理要素的时空变化分析对于了解和掌握地表的规律性有着重要的作用。利用地面站点观测、实地调查等传统方式获取数据,对地理要素进行时空变化分析是最常用的方法。但该类方法往往表现的是"点尺度"观测,不能在大尺度情况下准确地反映地表的时空变化信息。遥感卫星能以一定的时间间隔获得空间连续的对地"面尺度"观测数据,然而其特定的空间和时间分辨率使其获取的地表信息仍十分有限。同时地表的空间异质性和个别地表短时间内的快速变化,使得利用遥感数据对地理要素进行时空变化分析时,时空变化分析结果会随观测尺度而发生改变。本文从空间尺度和时间尺度两方面综述遥感数据时空尺度对地理要素的时空变化分析产生的影响和原因,并针对这些问题总结了减小时空尺度对结果不确定性影响的现行方法。可以通过多源遥感协同观测和反演、尺度转换、空间建模等方法减小空间尺度引起的不确定性;通过联合多时相遥感数据的方法减小时间尺度引起的不确定性。在实际应用中,应根据所观测地理要素的实际情况,综合分析选择合适的方法。     

地图数据缩编更新中道路数据匹配方法

用比例尺1∶1万的道路数据缩编更新比例尺1∶5万的相应数据,需要建立不同尺度、不同时态的道路目标间的匹配关系,以提取变化数据进行更新。通过分析道路目标间存在的分解、基本以及抽象的三个匹配层次,利用缓冲区分析和拓扑关系等手段开发了系列算法,进而完成了各目标间的匹配。实验表明,该匹配方法正确率高,实用性强,能满足缩编更新道路数据的要求。     

多源遥感影像配准技术分析

图像配准技术是近年来发展迅速的图像处理技术之一,是图像融合、目标提取与定位、变化监测、高分辨率影像重建等处理工作不可缺少的步骤。首先给出了多源遥感影像配准的概念和基本过程,然后着重从匹配基元、转换函数、相似性测度、匹配策略4个方面对国内外现有的影像配准技术和方法进行了分析和评述,最后指出了影像配准技术所面临的主要难题和发展方向。     

多源遥感影像配准技术分析

图像配准技术是近年来发展迅速的图像处理技术之一,是图像融合、目标提取与定位、变化监测、高分辨率影像重建等处理工作不可缺少的步骤.首先给出了多源遥感影像配准的概念和基本过程,然后着重从匹配基元、转换函数、相似性测度、匹配策略4个方面对国内外现有的影像配准技术和方法进行了分析和评述,最后指出了影像配准技术所面临的主要难题和发展方向.     

单窗算法的大气参数估计方法

根据地表热辐射传导方程,提出了一个简单可行且精度较高的专门用于从TM6数据中演算地表温度的方法——单窗算法.这一算法把大气和地表状态对地表热传导的影响直接包括在演算公式中.该方法需要两个大气参数进行地表温度的演算,即大气平均作用温度和大气透射率.本文论述这两个大气参数的估计方法:根据大气水分含量或地表附近空气湿度来估计大气透射率;通过分析标准大气剖面资料,尤其是大气水分和气温随高程的变化规律,根据地表温度推算大气平均作用温度.     

一种基于形状上下文特征匹配的线状要素Morphing方法

提出了一种基于上下文特征的形状匹配方法,并将其用于线状要素的Morphing变换。首先通过计算每个点的形状上下文,建立形状直方图,然后通过直方图匹配找到同名实体在大小比例尺下轮廓点的最佳匹配关系。根据点的匹配关系,得到对应线段。最后通过分段线性内插实现线状要素的连续尺度变换。实验结果表明,基于形状上下文的轮廓点集匹配方法不需要标志点或者关键点,适应性较强,可以有效地实现形状匹配,极大地提高Morphing变换的精度。     

基于正交变换的多通道遥感影像变化检测

针对多时相多通道遥感影像的变化检测问题，引入了多元统计中的典型相关分析方法，对遥感影像进行典型变换，并采用最小噪声比率变换对典型变换结果作后处理，得到差异影像，初步解决了将变化信息集中到少数分量中的问题。实验证实了该方法的有效性，并与主成分分析方法进行了比较。