Strain localization in sand: an overview of the experimental results obtained in Grenoble using stereophotogrammetry

Experimental results are presented from the extensive program of drained plane strain compression tests on sand carried out in Grenoble over the last two decades. Systematic analysis of photographs of the deforming specimen allowed for measuring deformations and determining strain fields throughout the test, that is: prior to, at, and after the onset of strain localization. The principles, details and accuracy of the procedure are described, as well as its suitability to properly depict the patterns of deformation. Findings concerning the occurrence and progression of strain localization are discussed. The issues of shear band orientation and thickness are addressed, as well as temporary and persistent complex localization patterns, and the volumetric behaviour inside a band after its formation. The influence of such variables as initial state of the sand (effective stress and relative density), specimen size and slenderness, as well as grain size, is discussed. Copyright © 2004 John Wiley & Sons, Ltd     

Fourcade: the Centenary of a Stereoscopic Method of Photographic Surveying

In the Preface to his book, The Four Faces of Fourcade, Clare Storrar (1990) wrote: "It is di.cult to appreciate the breadth and depth of Henry Georges Fourcade's intelligence and creative power. He was an intellectual giant, a phenomenon, whose theoretical and practical achievements have never received proper recognition. These were all the more remarkable because he began his original work on photogrammetry when science in South Africa was in its infancy, and he laboured alone far from libraries and other research facilities. His only higher academic training was in land surveying. He was adept in each of four sciences at various stages in his life, but, mainly because of his natural reserve, his reputation was highly compartmentalised. To foresters he was 'the most brilliant forestry officer of his time' to surveyors, he was exceptionally learned in theory and skilled in practice. Photogrammetry was a new subject, unheard of, except by a handful of scientists. In botany, which he took up seriously at the age of fifty-five, his work was highly regarded by leading botanists in South Africa and in Europe. All stood in awe of his extraordinary talent and ability. Some were frightened of him. But few were able—in fact, not even the best brains were wholly qualified—to grasp fully the tremendous intellectual stature and potential of this protean man."
This paper briefly describes the historic achievements of Henry Georges Fourcade, with the emphasis on his land surveying and, in particular, his photogrammetric contributions to science. The centenary of one of these, his proposal of a stereoscopic method of photographic surveying, occurs in October 2001.     

一种更严密的双介质立体摄影测量折射改正算法

提出一种更严密的双介质立体摄影测量物方坐标折射改正算法。该算法用水下目标的空中同名直线光线公垂线段的中点作为摄影测量交会点的理论位置,解决了空中同名直线光线延长线不相交情况下摄影测量交会点不存在导致的点位关系不确定性问题,使摄影测量交会点到真实物点的坐标折射改正公式能够严格推导出来。分析了空中同名直线光线不相交情况对物方大地坐标折射改正的不利影响,研究了摄影测量交会点与水下真实物点的相互位置关系,推导了水下目标点的水深和大地坐标计算公式(即折射改正公式),通过WorldView-2立体影像浅海海底地形测量试验对算法的正确性和测量精度进行验证。研究表明,不论水下目标的空中同名直线光线延长线是否相交,该算法都是适用的,且能显著改善水下目标的高程测量精度。     

Monitoring and reconstructing past biogeomorphic succession within fluvial corridors using stereophotogrammetry

Past fluvial biogeomorphic succession dynamics, i.e. reciprocal interactions and adjustments between vegetation growth and fluvial landform construction, were monitored and reconstructed using stereophotogrammetry. The four‐dimensional spatio‐temporal stereophotogrammetric analyses were based on the use of archival analogue and digital aerial photographs. First, we tested the relevance of the technique to produce floodplain digital terrain models (DTMs) and cover height models (CHMs) of the dynamic River Allier, France, and compared the models derived from photogrammetric procedures to field measurements for CHMs and to LiDAR data for DTMs. Automatic photogrammetric procedures tended to create inaccurate digital models with production of outliers, incomplete sectors and areas of confusion especially for analogue stereo‐pairs. Expert correction using stereoscopic viewing improved the vertical accuracy of the digital models, but the vegetation height tended to be underestimated: approximately 0.50 m for vegetation heights less than 10 m, up to 1.50 m for tree heights higher than 25 m. Second, we applied this method to a wooded point bar located on the channelized River Garonne, France. At the scale of the point bar, accurate biogeomorphic maps that show terrain and vegetation height changes in all three spatial dimensions were produced and accurate vegetation growth curves from the early stages of establishment until maturity were extracted. Assuming that a set of conditions is satisfied (e.g. spatial scale of investigation, quality of the photographs), our results show that the photogrammetric method applied in this research can be used operationally to detect and quantify present fluvial biogeomorphic dynamics (i.e. changes of topography and vegetation canopy height) within fluvial corridors of temperate rivers with satisfactory accuracy. Copyright © 2016 John Wiley & Sons, Ltd.     

The use of Roentgen stereophotogrammetry to study micromotion of orthopaedic implants

Roentgen stereophotogrammetry is the most accurate Roentgen technique for three-dimensional assessment of micromotion of orthopaedic implants. The reported accuracy of Roentgen Stereophotogrammetric Analysis (RSA) ranges between 0.05 and 0.5 mm for translations and between 0.15° and 1.15° for rotations. Because of the high accuracy of RSA, small patient groups are in general sufficient to study the effect on prosthetic fixation due to changes in implant design, addition of coatings, or new bone cements. By assessing micromotion of a prosthesis in a short-term (i.e. 2 years) clinical RSA study, a prediction can be made on the chance of long-term (i.e. 10 years) loosening of the prosthesis. Therefore, RSA is an important measurement tool to screen new developments in prosthetic design, and to prevent large groups of patients from being exposed to potentially inferior designs.In this article, the basics of the RSA technique are explained, and the importance of clinical RSA studies is illustrated with two examples of clinical RSA studies which RSA delivered very valuable information. Thereafter, two recent developments in RSA that have been implemented at Leiden University Medical Center are presented: digital automated measurements in RSA radiographs and model-based RSA.     

Double-camera measurements of plumes, applied to wind field characterization and dispersion studies

A stereophotogrammetric technique based on standard equipment to measure plume trajectories in sheared wind fields and/or complex terrain is shown here. The approach is to use existing visible plumes as tracers of opportunity of air flow. This technique was first developed as part of a multi-instrument field program intended for the experimental characterization of atmospheric dispersion in the complex coastal area of Bilbao in northern Spain. Emphasis is placed on the calibration method and the experimental procedures as well as on sources and margins of error. Finally, applications and joint usage with other techniques during several field programs are also presented.     

高分辨率星载遥感立体像对3D测量模型

由于具备立体测量功能的高分辨率卫星不断增多,使利用星载遥感影像立体像对获取DEM逐渐成为可能。与传统航空摄影测量相比,星载方式平台稳定,其姿态控制与测量精度较高,能充分保证3D测量的精度。对Quick-BirdI、KONOSS、POT5 3种卫星相似的立体成像方式进行研究,利用星历和姿态内插方法确定多中心投影的外方位元素初始值,利用前、后视共线方程及误差方程构建通用的立体测量数学模型,最后由若干控制点解算出立体测量所需定向参数。以SPOT5数据为例,进行外方位元素解算及模型误差分析,结果表明模型具有较好的3D测量精度。     

Photogrammetry using in-field calibration: a non-invasive tool for predicting sex and life stages tested on Hector's dolphins in the wild

Accurate data on sex and life stage are essential for building realistic population models, which in turn are essential for sustainable conservation management. This case study develops and validates an improved photogrammetry method that allows for in-field calibration. The method was used to measure Hector's dolphins’ dorsal fins in the wild. Seven independent measurements of one dolphin resulted in a coefficient of variation of 1.39% for fin base length and 2.33% for fin height. Test measurements on shore at different distances and angles resulted in a mean error smaller than 1% up to a distance of 10?m and an angle of 40°. Dorsal fin dimensions from necropsied Hector's dolphins were analysed to evaluate the potential of predicting sex and life stage based on a dorsal fin measured in the wild. Dorsal fin shape was significantly related to sex. However, sex estimations based on this model turned out to be not accurate enough to replace traditional sexing methods for Hector's dolphins. Fin base length was significantly related to life stage for females. Estimations based on this model appear to be accurate.     

WorldView-2影像双介质摄影测量的浅海地形测绘试验

主要研究利用高分辨率WorldView-2卫星影像和双介质立体摄影测量方法进行浅海地形测绘的可行性,同时解决双介质立体摄影测量精定位算法(即折射改正算法)适用性差的问题。首先依据通用的双介质物像几何关系,提出了一种普适的双介质立体摄影测量折射改正算法;然后以海南省三沙市甘泉岛、珊瑚岛周围浅海区域为试验场,利用两个地区的WorldView-2立体影像,运用双介质立体摄影测量方法进行了浅海地形测绘试验。试验成功提取到了两个地区浅海海底的数字高程模型(DEM)。其中,甘泉岛地区的浅海DEM精度达到2.08 m(剔除其中的高程异常点后的结果)。研究表明:提出的折射改正算法,无论"空中同名光线延长线是否相交"都是适用的,且能改善浅海地形测绘精度。在水体清澈、无海浪情况下,利用相应的WorldView-2立体影像和双介质立体摄影测量方法进行浅海地形测绘是可行的。