Multi-point matching along vertical lines in SPOT images

Abstract

Digital elevation models(DEMs) are measured in SPOT images with a digital matching technique. A multi-point matching method developed by the author in earlier work is reformulated from epipolar geometry with the stereoparallaxes in one of the images used as unknowns, to SPOT geometry with the elevations as unknowns. Constraints minimizingthe curvature and the slope of the Computed DEM are investigated, as well as the use of data snooping, low-pass filtering and an alternative logarithmic grey level function. The investigatedimage pair was a stereo SPOT pair from Stockholm, with a rather poor base-to-height ratio of 0·29. All 2073 investigated points were compared with heights obtained from the official Swedish maps, scale 1:10000, with a 5 m contour interval. The results point towards a r.m.s. matching accuracy around 0·15-0·20 pixels in this image material.     

DEM generation using Ziyuan-3 mapping satellite imagery without ground control points

ABSTRACT

This article proposes a digital elevation model (DEM) generation approach using the Shuttle Radar Topography Mission (SRTM) DEM as the elevation constraint without ground control points. First, during the process of image block adjustment, we took advantage of the relatively high vertical accuracy of the SRTM-DEM in flat terrain regions and applied effective constraints on the object-space elevation-corrected value of tie points using the SRTM-DEM, achieving improved vertical accuracy for large-scale block adjustments. Subsequently, for the DEM matching process, multiple two-linear array stereo image pairs were obtained from along-track and across-track images with different look angles over the same region after the block adjustment. Then, the matching result of each stereo image pair underwent weighted fusion, before being used to generate the final DEM product. This approach can effectively enhance the matching quality and grid density of the final DEM product. The DEM generation experiment, using Ziyuan-3 images covering 186,000 km² of Hubei Province, China, showed that the matching quality of the 10 m grid DEM was excellent. The vertical root mean square errors were 1.5 m in the flat regions and 2.96 m in the mountainous regions, thus achieving China’s 1:25,000 scale specification requirement for DEM products.     

Photogrammetric processing of high-resolution airborne and satellite linear array stereo images for mapping applications

This article introduces a mathematical model for photogrammetric processing of linear array stereo images acquired by high-resolution satellite imaging systems such as IKONOS. The experimental result of the generation of simulated IKONOS stereo images based on photogrammetric principles, IKONOS imaging geometry and a set of georeferenced aerial images is presented. An accuracy analysis of ground points derived from the simulated IKONOS stereo images is performed. The impact of the number of GCPs (ground control points), distribution of GCPs, and image measurement errors on the ground point accuracy is investigated. It is concluded that an accuracy of ground coordinates from 2 m to 3 m is attainable with GCPs, and 5 m to 12 m without GCPs. Two data sets of HRSC (high resolution stereo camera) and MOMS (modular opto-electronic multispectral stereo-scanner)-2P are also utilized to test the model and system. The presented data processing method is a key to the generation of mapping products such as digital terrain models (DEM) and digitial shorelines from high-resolution satellite images.     

Terrain resources surveys by visual monoscopic and stereoscopic interpretation of FGEOS images

Abstract

Monoscopic and stereoscopic interpretation of FGEOS (First Generation Earth Observation Satellites) images were applied comparatively in order to divide the region of Central Peloponnesos (Greece) into physiographic units for thematic mapping concerning geomorphology, soils and land use. A stereo pair of Landsat-1 black and white prints and a false-colour print at 1:250000 scale were used in order (1) to construct a reconnaissance physiographic map, (2) to construct a land use map and (3) to reconsider the monoscopic interpretation techniques, because of the newly-developed SPOT stereo capability and 10 × 10 m ground resolution. The known problems reported from the FGEOS 79 × 79 m resolution could reduce the effectiveness of any interpretation method. However the results show that the stereoscopic interpretation and physiographic analysis of satellite images improve the accuracy of boundaries and increase the number of mapping units, and consequently they are expected to minimize field work, laboratory analysis, field staff and the total cost of surveying.     

双目区域视差快速计算及测距算法

目的 双目测距对水面无人艇自主避障以及视觉侦察具有重要意义,但视觉传感器成像易受光照环境及运动模糊等因素的影响,基于经典Census变换的立体匹配代价计算方法耗时长,且视差获取精度差,影响测距精度。为了提高测距精度并保证算法运行速度,提出一种用于双目测距的快速立体匹配算法。方法 基于传统Census变换,提出一种新的比特串生成方法,在匹配点正方形支持窗口的各边等距各选3个像素点,共选出8个像素点,这8个像素点两两比较生成一个字节的比特串。将左右视场中的匹配点与待匹配点的比特串进行异或,得到两点的汉明距离,在各汉明距离中找到距离最小的像素点作为匹配像素点,两像素点的横坐标差为视差。本文采用区域视差计算的方法,在左右视场确定同一目标区域后进行视差提取和滤波,利用平均视差计算目标的距离。结果 本文算法与基于传统Census变换的立体匹配视差获取方法相比,在运算速度方面优势明显,时间稳定在0.4 s左右,用时仅为传统Census变换算法的1/5。在Middlebury数据集中的图像对teddy和cones上进行的算法运行时间对比实验中,本文基于Census变换改进的算法比已有的基于Census变换的匹配算法在运行时间上快了近20 s。在实际双目测距实验中,采用本文算法在1019 m范围内测距误差在5%以内,根据无人艇的运动特点和避障要求,通过分析可知该算法的测距精度可以满足低速无人艇的避障需求。结论 本文给出的基于改进Census变换的匹配算法在立体匹配速度上有大幅提高,提取目标视差用于测距,实际测距结果表明,本文算法能够满足水面无人艇的视觉避障要求。     

不同模式Radarsat 影像DEM 提取及精度比较

利用摄影测量方法进行DEM 提取是热带雨林地区雷达应用方向之一。以热带雨林地区平地、丘陵和山地混合地形区为研究对象, 收集了F、S 和W 等不同波束模式的Radarsat-1 SAR 影像9 景, 组合成6 个不同类型的立体像对, 进行DEM 提取, 探讨基于距离ö多普勒构像方程的Radarsat 影像的DEM 提取方法。通过对DEM 结果进行精度验证和比较, 认为提取的DEM 精度受多种因素影响, 同种波束模式的立体配置, 立体交会角越大,DEM 精度越高; 对于地表起伏较小的平地,DEM 精度要高于丘陵山地区, 该研究区DEM 精度的平均误差可以达到14 m 左右,RMSE 可以达到29 m 左右。     

Block bundle adjustment of Ikonos in-track images

This letter presents a block bundle adjustment process applied to four Ikonos Geo-product in-track images with few ground control points (GCPs) over a high mountainous area of Venezuela. Various configurations of block bundle adjustment (1-4 images and different GCPs) were evaluated with independent check points. Whatever the number of images, the block bundle adjustment results were consistent with planimetric errors of about @ 5 m to - 7 m. Part of this error was due to the error of the ground data. The evaluation of the final ortho-mosaic with 1:1000 vector lines gives an approximation of relative and absolute errors to be - 2 m and - 3 m to - 4 m with maximum errors of - 6 m and - 10 m, respectively.     

Stereo rectification of pushbroom satellite images by robustly estimating the fundamental matrix

ABSTRACT

Stereo rectification is one of the most important steps for stereo matching and subsequently for digital surface model generation from satellite stereo images. This study proposes a new framework to rectify two pushbroom images along the epipolar geometry in order to omit the vertical parallax between two images. Here, we assume the interior and relative parameters between the two pushbroom images are not known and the images can be taken at different dates. Traditional stereo rectification methods of pushbroom images require metadata such as rational polynomial coefficients (RPCs), parameters of physical sensor model or ground control points (GCPs). In this study, we develop an image-based framework for stereo rectification, which works without the need for such data. In the proposed framework, the correspondences are densely extracted by a tilling strategy, and then the fundamental matrix is robustly estimated by two geometric constraints. Both affine and projective fundamental matrices could be used for stereo rectification from pushbroom stereo images. The results on IRS P5, World view III, GeoEye and IKONOS stereo pairs as well as on multi-date stereo images demonstrate that the pushbroom images are rectified with sub-pixel accuracy.     

由航空影像自动重建大范围3维地形

目的 针对由航空影像自动生成大范围3维地形的立体模型配准问题,提出一种自动配准全部立体模型的方法,从而生成大范围3维地形。方法 首先由相邻影像构建独立的立体模型;然后根据特征匹配同名点在公共影像上的坐标对应关系,自动提取相邻模型的连接点;通过循环遍历搜索,自动配准全部立体模型,进而构建全航摄区的大范围3维地形。结果 采用两组数据进行实验,结果显示,两组数据全部3维模型的均方配准误差分别为5.20像素和2.63像素。本文方法生成的大范围地形的相对精度较高;对第2组数据的结果采用控制点进行绝对定向,并用检查点进行精度评估,结果显示全部检查点的均方平面和高程误差分别为0.326 m和0.502 m,生成的大范围地形达到了较高的绝对精度。结论 本文方法可自动化执行,仅需输入一系列有一定重叠的航空影像,即可自动生成按一定方式组织的大范围3维地形产品。该方法生成的大范围地形既可用于3维场景浏览,也可用于地形量测,但不适用于由激光扫描获取的点云数据的配准。     

Combining Structure from Motion and close-range stereo photogrammetry to obtain scaled gravel bar DEMs

ABSTRACT

Digital elevation models (DEMs) have been increasingly applied in topographic studies in areas such as physical geography and hydraulic engineering. Several methods have been proposed to reconstruct DEMs, including classic close-range stereo photogrammetry and the more novel Structure from Motion (SfM) methodology. Past published studies tend to apply SfM to large-scale environmental processes, whilst classic close-range stereophotogrammetry is focusing on detailed small-scale applications. However, SfM requires multiple ground control points (GCPs) to allow for proper DEM scaling. The larger the study area, the more GCPs are required, resulting in increased operational complexity and time-consuming application of SfM. As the accuracy of the DEM depends on the equipment used to measure GCPs, this can also result in a cost-expensive operation. In the present study, we introduce a combined SfM and close-range stereo photogrammetry application, with the close-range stereo photogrammetry results serving as a control for providing scale, thus eliminating the need for traditional GCPs. To validate our methodology, we studied a 40 m long gravel bar. We used GoPro Hero 3 cameras for SfM measurements and replaced GCPs by DEMs obtained through close-range stereo photogrammetry with a Nikon D5100 camera pair in stereo. In addition to using photo-mode frames, we also studied the quality of DEMs obtained with GoPro Hero 3 video-mode frames, and show how the DEM quality is reduced due to the smaller image format, hence coarser point cloud spacing, which eventually results in a convex curvature when image overlap was increased. Our results show that it is possible to collect high-quality topographic surface data by only using cameras, and alleviate the need for GCPs. The proposed workflow reduces the complexity, time, and resource demands associated with deploying GCPs and necessary independent geo-referencing, ensuring that digital photogrammetry will continue to gain popularity for field surveying.     

用立体影像匹配和数学形态变换自动生成DEM

数学形态学已经成为计算机图象处理的一个重要研究领域 ,并在遥感影像分析中得到了卓有成效的应用 .将数学形态学的理论方法引入了建立数字高程模型 (DEM)的研究 ,提出了一种利用立体象对 ,自动匹配识别同名点并提取地表三维坐标 ,继而用数学形态变换建立 DEM的方法 .该方法首先利用正交小波变换对影像进行分解、重建、特征提取 ,并利用影像与特征结合的匹配方法进行亚像素匹配 ;然后根据匹配得到离散的地面点数据 ,用形态变换的方法构建泰森多边形、Delaunay三角网 (TIN) ;最后内插成格网 DEM.试验证明 ,该方法具有数据结构简单、运算速度快、精度好等优点 .     

Deriving terrain and textural information from stereo RADARSAT data for mountainous land cover mapping

A new procedure is proposed for land cover classification in a mountainous area using stereo RADARSAT-1 data. The method integrates a few types of information that can be extracted from the same stereo RADARSAT images: (1) the Digital Elevation Model (DEM) generated from the stereo RADARSAT images; (2) terrain information (elevation, slope and aspect) extracted from the derived DEM; and (3) textural information derived from the same RADARSAT images. An Artificial Neural Network (ANN) classifier is applied for the land cover classification. Performance of the proposed method is evaluated using a mountainous study area in Southern Argentina, where there is a lack of up-to-date information for environmental monitoring. The results show that the integration of textural and terrain information can greatly improve the accuracy of the classification using the ANN classifier. It demonstrates that stereo RADARSAT images provide valuable data sources for land cover mapping, especially in mountainous areas where cloud cover is a problem for optical data collection and topographical data are not always available.     

GCP acquisition using simulated SAR and evaluation of GCP matching accuracy with texture features

Abstract

A method for ground control point (GCP) acquisition using a simulated synthetic aperture radar (SAR) image derived from a digital elevation model (DEM) is proposed. Also proposed is a method for the evaluation of the accuracy of GCP matching with texture features from a reference GCP chip image. Results from experiments with simulated GCP chip images as reference images and geometrically distorted GCP chip images, derived using simulated SAR images as current images, show good coincidence with GCP matching accuracy in terms of pixel distances between matched GCP points in reference and current chip images and texture features. In particular, the correlation coefficient between the angular second moment (ASM) and the matching accuracy is 0.757, followed by Ent (entropy), Horn (homoginiety), Dis (dissimilarity), Con (contrast), Var (variability coefficient) and Chi (Chi-square), for the skewed images while for the rotated images, Dis shows the highest correlation of 0.628, followed by Horn, Asm, Con, Ent, Chi and Var. Based on the proposed methods, one can easily generate GCP chips images from a DEM, and also evaluate GCP matching accuracy with texture features of simulated SAR from a GCP chip image.     

结合同场景立体图对的高质量深度图像重建

目的 越来越多的应用依赖于对场景深度图像准确且快速的观测和分析,如机器人导航以及在电影和游戏中对虚拟场景的设计建模等.飞行时间深度相机等直接的深度测量设备可以实时的获取场景的深度图像,但是由于硬件条件的限制,采集的深度图像分辨率比较低,无法满足实际应用的需要.通过立体匹配算法对左右立体图对之间进行匹配获得视差从而得到深度图像是计算机视觉的一种经典方法,但是由于左右图像之间遮挡以及无纹理区域的影响,立体匹配算法在这些区域无法匹配得到正确的视差,导致立体匹配算法在实际应用中存在一定的局限性.方法 结合飞行时间深度相机等直接的深度测量设备和立体匹配算法的优势,提出一种新的深度图像重建方法.首先结合直接的深度测量设备采集的深度图像来构造自适应局部匹配权值,对左右图像之间的局部窗立体匹配过程进行约束,得到基于立体匹配算法的深度图像;然后基于左右检测原理将采集到的深度图像和匹配得到的深度图像进行有效融合;接着提出一种局部权值滤波算法,来进一步提高深度图像的重建质量.结果 实验结果表明,无论在客观指标还是视觉效果上,本文提出的深度图像重建算法较其他立体匹配算法可以得到更好的结果.其中错误率比较实验表明,本文算法较传统的立体匹配算法在深度重建错误率上可以提升10％左右.峰值信噪比实验结果表明,本文算法在峰值信噪比上可以得到10 dB左右的提升.结论 提出的深度图像重建方法通过结合高分辨率左右立体图对和初始的低分辨率深度图像,可以有效地重建高质量高分辨率的深度图像.     

Validation and comparison of different techniques for the derivation of digital elevation models and volcanic monitoring (Vulcano Island,Italy)

High accurate digital elevation models (DEM) acquired periodically over a volcanic area can be used for monitoring crustal deformations. Airborne stereoscopic photography is a powerful tool for the derivation of high resolution DEM, especially when combined with Global Positioning System (GPS). We analyse data acquired on Vulcano Island (Italy) to assess the performance of two photogrammetry methods for DEM generation. The first method is based on automatic digital processing of scanned airborne stereo images from a film camera (Wild RC20). In the second method digital stereo data from the multi-spectral High Resolution Stereo Camera-Airborne (HRSC-A) are used. Accuracy assessment through comparison with kinematic GPS height profiles shows that both DEMs have accuracy on the order of few decimetres. Direct comparison of the two DEMs on the La Fossa volcanic cone provides a standard deviation of the residuals of 78 cm. Residuals greater than two metres between the two DEMs acquired at one year interval are locally evidenced in unstable areas with uneven morphology. The application of photogrammetric DEMs is also discussed within a SAR interferometry study carried out on Vulcano Island to evaluate the potentialities of such techniques for ground deformation monitoring. Although accuracy better than 1 m or 2 m is not required for satellite SAR interferometry, we show how the precise photogrammetric DEMs could still significantly improve SAR interferograms of Vulcano Island.     

A mixed spaceborne sensor approach for surface modelling of an urban scene

Three-dimensional (3D) surface models are vital for sustainable urban management studies, and there is a nearly unlimited range of possible applications. Along- or across-track pairs from the same set of sensor imagery may not always be available or economical for a certain study area. Therefore, a photogrammetric approach is proposed in which a digital surface model (DSM) is extracted from a stereo pair of satellite images, acquired by different sensors. The results demonstrate that a mixed-sensor approach may offer a sound alternative to the more established along-track pairs. However, one should consider several criteria when selecting a suitable stereo pair. Two cloud-free acquisitions are selected from the IKONOS and QuickBird image archives, characterized by sufficient overlap and optimal stereo constellation in terms of complementarity of the azimuth and elevation angles. A densely built-up area in Istanbul, Turkey, covering 151 km² and with elevations ranging between sea level and approximately 160 m is presented as the test site. In addition to the general complexity of modelling the surface and elevation of an urban environment, multi-sensor image fusion has other particular difficulties. As the images are acquired from a different orbital pass, at a different date or instant and by a different sensor system, radiometric and geometric dissimilarities can occur, which may hamper the image-matching process. Strategies are presented for radiometric and geometric normalization of the multi-temporal and multi-sensor imagery and to deal with the differences in sensor characteristics. The accuracy of the generated surface model is assessed in comparison with 3D reference points, 3D rooftop vector data and surface models extracted from an along-track IKONOS stereo pair and an IKONOS triplet. When compared with a set of 35 reference GPS check points, the produced mixed-sensor model yields accuracies of 1.22, 1.53 and 2.96 m for the X, Y and Z coordinates, respectively, expressed in terms of root mean square errors (RMSEs). The results show that it is feasible to extract the DSM of a highly urbanized area from a mixed-sensor pair, with accuracies comparable with those observed from the DSM extracted from an along-track pair. Hence, the flexibility of reconstructing valuable elevation models is greatly increased by considering the mixed-sensor approach.     

基于WorldView-2制备大野口流域高分辨率DEM及精度分析

在全野外GPS地面控制点基础上,对WorldView-2影像自带RPC文件进行校正,利用数字摄影测量软件系统在立体模型上通过影像自动匹配技术快速提取黑河流域上游大野口子流域1∶5 000比例尺数字高程模型(DEM)。由于区域地形复杂、交通不便,研究区南部无地面控制点覆盖。基于立体模型交互式操作,匹配60个均匀分布高精度影像连接点,提高了DEM自动提取精度。并在对阴坡森林覆盖区、大野口水库等重点区域进行DEM编辑基础上,辅助地形特征点和线数据提高了成果精度。由15个外业控制点、12个模型保密点组成的检查点进行定量DEM验证,结果表明:两组高程中误差最大为1.9 m,达到该比例尺山地一级精度2.5 m的要求。
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Automatic map-guided extraction of roads from SPOT imagery for cartographic database updating

Abstract

The launching of the Satellite Probatoire d'Observation de la Terre (SPOT) has permitted the acquisition of images with a relatively fine ground resolution (10 and 20 m). Such improvement has brought forward the possibility of medium-scale mapping using such data. In this paper we are proposing an automatic approach to 1:50000 scale planimetric data revision using the panchromatic channel of SPOT imagery (10m of ground resolution). A software package has been developed that performs an automatic map-guided extraction of objects from the SPOT image for map revision purposes. The programs are fully described along with some conclusive results through the updating of the road network on a topographic map. An attempt has been made to give a preview of how such a map-guided approach can be extended to other linear features and possibly two-dimensional objects as well.     

Using satellite remote sensing for DEM extraction in complex mountainous terrain: Landscape analysis of the Makalu Barun National Park of eastern Nepal

The design and management of national parks and other protected areas requires a broad base of physiographic and geo-ecological information about the landscape. This paper evaluates the effectiveness of satellite remote sensing for photogrammetric stereo-mapping and digital elevation model (DEM) extraction within remote mountainous terrain. As a case study, a landscape analysis of the Makalu Barun National Park and Conservation Area of east Nepal (27.5° N, 87.0° E) was examined. The study area is a highly complex and rugged mountain landscape, with extreme topographic relief and an elevation gradient spanning more than 8300 m. A DEM extracted from stereo SPOT imagery resulted in a median disagreement of 58 m when compared to a DEM generated from a conventionally digitized GIS dataset of topographic contours (scale=1:250 000). Visual comparison of the two DEMs showed substantial agreement at the landscape scale, while larger scale comparison of 100 m contours revealed some localized differences. The SPOT extracted DEM provided equal or better basis for orthorectification of satellite imagery when compared to the conventional DEM. Derivative landscape analysis outputs, such as hydrological modelling, drainage networks and watershed boundaries, compared well with results based upon the conventional dataset. Intermediate map products useful for field research and mapping included production of an orthorectified satellite base-map image. Additionally, a fused multisensor high resolution image of the study area, combining Landsat Thematic Mapper (TM) and SPOT imagery at 10 m resolution, was orthorectified to produce a false-colour satellite image map highlighting the spectral discrimination between land cover classes.     

Surface motion of mountain glaciers derived from satellite optical imagery

A complete and detailed map of the ice-velocity field on mountain glaciers is obtained by cross-correlating SPOT5 optical images. This approach offers an alternative to SAR interferometry, because no present or planned RADAR satellite mission provides data with a temporal separation short enough to derive the displacements of glaciers. The methodology presented in this study does not require ground control points (GCPs). The key step is a precise relative orientation of the two images obtained by adjusting the stereo model of one “slave”' image assuming that the other “master” image is well georeferenced. It is performed with numerous precisely-located homologous points extracted automatically. The strong ablation occurring during summer time on the glaciers requires a correction to obtain unbiased displacements. The accuracy of our measurement is assessed based on a comparison with nearly simultaneous differential GPS surveys performed on two glaciers of the Mont Blanc area (Alps). If the images have similar incidence angles and correlate well, the accuracy is on the order of 0.5 m, or 1/5 of the pixel size. Similar results are also obtained without GCPs. An acceleration event, observed in early August for the Mer de Glace glacier, is interpreted in term of an increase in basal sliding. Our methodology, applied to SPOT5 images, can potentially be used to derive the displacements of the Earth's surface caused by landslides, earthquakes, and volcanoes.