正射影像应急快速更新方法研究

随着数字摄影测量技术的发展,正射影像的制作及更新技术已经走向成熟,但是,针对局部影像进行快速更新还缺乏研究及实践.本文从应急测绘保障实际需要出发,提出一种对正射影像进行局部快速更新的方法.实验结果验证了本文方法的有效性和可行性.     

质心法在航空影像框标定位中的应用

航片框标定位的精度直接影响摄影测量测图的质量,传统的基于影像匹配的框标定位算法精度只能达到像素级。文中提出一种模板匹配与质心法相结合的航片框标定位方法,先利用模板匹配进行概略定位,再利用质心法进行框标点的精确定位,将精度提高到亚像素级。实验证明该方法可以有效地提高精度。     

遥感影像匹配中的反定位误匹配剔除算法

图像匹配的准确率和精度一直是瓶颈问题,直接制约遥感影像的自动化处理。在简要分析现有典型误匹配剔除方法的基础上,提出了能够适应遥感影像自动化匹配与处理的REPRAM(Reverse Positioning Re-fining Algorithm in Matching)算法,给出了REPRAM排除法和优选法的原理和性能分析,在不需要相机的外参数、内参数以及控制点的情形下,相对分离了正确同名点与错误同名点之间的相互影响,尽量保留正确同名点,最大限度剔除错误同名点。大量遥感影像和航拍影像测试表明,算法的稳健性强,在初始匹配正确率为30%的情况下,在设定误差容限内,算法的可靠率仍能在99.5%以上。     

3D Motion parameters determination based on binocular sequence images

Exactly capturing three dimensional (3D) motion information of an object is an essential and important task in computer vision, and is also one of the most difficult problems. In this paper, a binocular vision system and a method for determining 3D motion parameters of an object from binocular sequence images are introduced. The main steps include camera calibration, the matching of motion and stereo images, 3D feature point correspondences and resolving the motion parameters. Finally, the experimental results of acquiring the motion parameters of the objects with uniform velocity and acceleration in the straight line based on the real binocular sequence images by the mentioned method are presented.     

Image relaxation matching based on feature points for DSM generation

In photogrammetry and remote sensing, image matching is a basic and crucial process for automatic DEM generation. In this paper we presented a image relaxation matching method based on feature points. This method can be considered as an extention of regular grid point based matching. It avoids the shortcome of grid point based matching. For example, with this method, we can avoid low or even no texture area where errors frequently appear in cross correlation matching. In the mean while, it makes full use of some mature techniques such as probability relaxation, image pyramid and the like which have already been successfully used in grid point matching process. Application of the technique to DEM generaton in different regions proved that it is more reasonable and reliable.     

GF-4序列图像的云自动检测

以高分四号(GF-4)卫星L1级标准分幅数据产品提供高精度的云检测产品为目的,研究针对地球同步轨道卫星数据的云检测算法,改进自动阈值以适应同日不同时刻成像数据的辐射亮度与地表反射特性的变化差异。利用GF-4卫星凝视成像方式获取的同区域序列图像以及云在不同图像上的运动特性,结合自动阈值与SavitzkyGolay(SG)滤波修正检测结果中的误检。算法的两个关键预处理,一是通过自动的几何配准解决未经几何校正的分幅数据之间像素位置对应的问题,二是通过基于典型相关变换自动提取序列图像之间的伪不变特征点集,进而利用相对辐射归一减小了不同时刻成像数据之间的辐射差异。通过内蒙古自治区东部及长江中下游区域70余组数据对算法进行验证,整体上获得了稳定的结果与精度,并且基于序列图像的云检测算法在云边界、高亮地表及薄云区域的检测精度整体优于单幅自动阈值的检测结果。结果表明算法精度上满足GF-4云检测数据产品需求,且算法自动化程度高,便于工程化的数据生产。     

一种综合利用像方和物方信息的多影像匹配方法

A novel method for multi-image matching by synthesizing image and object-space information is proposed. Firstly, four levels of image pyramids are generated according to the rule that the next pyramid level is generated from the previous level using the average gray values of the 3 by 3 pixels, and the first level of pyramid image is generated from the original image. The initial horizontal parallaxes between the reference image and each searching image are calculated at the highest level of the image pyramid. Secondly, corresponding image points are searched in each stereo image pair from the third level of image pyramid, and the matching results in all stereo pairs are integrated in the object space, by which the mismatched image points can be eliminated and more accurate spatial information can be obtained for the subsequent pyramid image matching. The matching method based on correlation coefficient with geometric constraints and global relaxation matching is introduced in the process of image matching. Finally, the feasibility of the method proposed in this paper is verified by the experiments using a set of digital frame aerial images with big overlap. Compared with the traditional image matching method with two images, the accuracy of the digital surface model (DSM) generated using the proposed method shows that the multi-image matching method can eliminate the mismatched points effectively and can improve the matching success rate significantly. Supported by the National Natural Science Foundation of China (Nos. 40771176, 40721001).     

Performance of dense digital surface models based on image matching in the estimation of plot-level forest variables

Recent research results have shown that the performance of digital surface model extraction using novel high-quality photogrammetric images and image matching is a highly competitive alternative to laser scanning. In this article, we proceed to compare the performance of these two methods in the estimation of plot-level forest variables. Dense point clouds extracted from aerial frame images were used to estimate the plot-level forest variables needed in a forest inventory covering 89 plots. We analyzed images with 60% and 80% forward overlaps and used test plots with off-nadir angles of between 0° and 20°. When compared to reference ground measurements, the airborne laser scanning (ALS) data proved to be the most accurate: it yielded root mean square error (RMSE) values of 6.55% for mean height, 11.42% for mean diameter, and 20.72% for volume. When we applied a forward overlap of 80%, the corresponding results from aerial images were 6.77% for mean height, 12.00% for mean diameter, and 22.62% for volume. A forward overlap of 60% resulted in slightly deteriorated RMSE values of 7.55% for mean height, 12.20% for mean diameter, and 22.77% for volume. According to our results, the use of higher forward overlap produced only slightly better results in the estimation of these forest variables. Additionally, we found that the estimation accuracy was not significantly impacted by the increase in the off-nadir angle. Our results confirmed that digital aerial photographs were about as accurate as ALS in forest resources estimation as long as a terrain model was available.     

一种基于分块策略的SIFT特征快速提取与匹配方法

通过研究基于GPGPU的SIFT特征匹配,提出一种通过分块处理实现大面阵遥感影像快速匹配的方法。首先采用鲁棒性强的随机采样一致性算法来估计待匹配影像间的单应关系并剔除误匹配点;然后通过单应关系找到待匹配影像间的重叠区域,进而实现大面阵遥感影像的分块SIFT特征提取和匹配。试验证明该算法可较快提取相应航摄测区的同名像点,为后续进行的光束法区域网平差提供了鲁棒的数据源。     

融合嫦娥一号CCD影像与DEM数据的月球撞击坑自动提取和识别

针对现阶段月球撞击坑定量信息提取不足和误提取的问题,本文提出了一种融合CCD影像和DEM数据进行撞击坑的自动提取及识别的算法。（1）在太阳光照下,撞击坑的影像特征满足特定的规律,通过条件匹配在CCD影像中提取撞击坑;（2）在DEM中,利用撞击坑坑壁点的坡向值的连续性,对影像中误提取的撞击坑进行剔除;（3）在DEM中,利用撞击坑边缘点法向量的突变性,提取撞击坑边缘点并进行拟合,计算撞击坑的参数,通过坑底点云所占比例以及剖面线特征识别撞击坑的类型。经过“嫦娥一号”影像与DEM数据的验证,该算法在高纬度月球撞击坑分布均匀的区域应用效果较好。