https://pure.aber.ac.uk/portal/files/4916016/Westoby_et_al._GEOMORPH_2012_Accepted.pdf

‘Structure-from-Motion’ photogrammetry: A low-cost, effective tool for geoscience applications

We first provide an overview of 3-D shape measurement us- ing various optical methods. Then we focus on structured light tech- niques where various optical configurations, image acquisition tech- niques, data postprocessing and analysis methods and advantages and limitations are presented. Several industrial application examples are presented. Important areas requiring further R&D are discussed. Finally, a comprehensive bibliography on 3-D shape measurement is included, although it is not intended to be exhaustive. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)00101-X)

Overview of three-dimensional shape measurement using optical methods

In this paper the main problems and the available solutions are addressed for the generation of 3D models from terrestrial images. Close range photogrammetry has dealt for many years with manual or automatic image measurements for precise 3D modelling. Nowadays 3D scanners are also becoming a standard source for input data in many application areas, but image-based modelling still remains the most complete, economical, portable, flexible and widely used approach. In this paper the full pipeline is presented for 3D modelling from terrestrial image data, considering the different approaches and analysing all the steps involved.

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Image-based 3d modelling: a review

Camera calibration has always been an essential component of photogrammetric measurement, with self-calibration nowadays being an integral and routinely applied operation within photogrammetric triangulation, especially in high-accuracy close-range measurement. With the very rapid growth in adoption of off-the-shelf digital cameras for a host of new 3D measurement applications, however, there are many situations where the geometry of the image network will not support robust recovery of camera parameters via on-the-job calibration. For this reason, stand-alone camera calibration has again emerged as an important issue in close-range photogrammetry, and it also remains a topic of research interest in computer vision. This paper overviews the current approaches adopted for camera calibration in close-range photogrammetry and computer vision, and discusses operational aspects for self-calibration. Also, the results of camera calibrations using different algorithms are summarized. Finally, the impact of chromatic aberration on modelled radial distortion is touched upon to highlight the fact that there are still issues of research interest in the photogrammetric calibration of consumer-grade digital cameras.

Digital camera calibration methods: Considerations and comparisons

Corriger les images de la distorsion des chambres de prises de vues a ete une preoccupation importante des usagers, aussi longtemps qu'ils ont voulu utiliser ou reconstituer fidelement les informations observees. La cartographie a ete initialement la principale application. Tandis que cette tâche se poursuit de nos jours, d'autres applications necessitent egalement un etalonnage precis des chambres, telles que les determinations tridimensionnelles a courte distance et de nombreuses autres mesures a deux dimensions. Dans le passe, les chambres utilisees etaient peu nombreuses et tres onereuses tandis qu'aujourdhui une grande societe industrielle aura normalement de nombreuses cameras bon marche qu'il utilisera pour des travaux de mesures tres importants. On se sert de nos jours de cameras beaucoup plus qu'on ne le fit jamais, mais l'âge d'or de l'etalonnage des chambres de prises de vues aeriennes pour la cartographie est desormais termine. On examine dans cet article quelques uns des essais et des developpements-cles et on les remet en perspective. On y met en particulier en evidence les forces sous-jacentes qui ont preside a chaque amelioration.

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The Development of Camera Calibration Methods and Models

Signalizing points of interest on the object to be measured is a reliable and common method of achieving optimum target location accuracy for many high precision measurement tasks. In photogrammetric metrology, images of the targets originate from photographs and CCD cameras. Regardless of whether the photographs are scanned or the digital images are captured directly, the overall accuracy of the technique is partly dependent on the precise and accurate location of the target images. However, it is often not clear which technique to choose for a particular task, or what are the significant sources of error. The research described in this paper describes aspects of target recognition, thresholding, and location. The results of a series of simulation experiments are used to analyze the performance of subpixel target location techniques such as: centroiding; Gaussian shape fitting; and ellipse fitting, under varying conditions.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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Comparison of some techniques for the subpixel location of discrete target images

On a longtemps considere le point principal comme etant l'un des parametres fondamentaux dans l'etalonnage des chambres de prises de vue. A l'epoque ou l'on utilisait des chambres aeriennes a films ou terrestres a grand format on pouvait determiner le point principal par divers procedes avec une exactitude de + 10 μm (Carman et Brown, 1961) et l'on estimait que c'etait suffisant. Mais ces chambres aeriennes constituaient des equipements de precision, onereux, specialement concus, dont le montage etait soigne et la position du point principal determinee avec des tolerances fixees. A l'epoque du numerique, les photogrammetres, ainsi que de nombreux autres usagers, utilisent des cameras qui n'ont pas ete exactement concues ni realisees pour la photogrammetrie. Dans ces cameras, les constructeurs ne disposent d'aucune norme dans le montage de l'objectif pour respecter une position definie par rapport au plan de l'image, ni pour aligner les differents verres de l'objectif entre eux avec precision. En fait, on peut meme s'ecarter du centre du capteur d'un pourcentage important de la dimension de ce capteur (jusqu'a 10 pour cent dans le cas de quelques objectifs a zoom (Burner, 1995)). On examine dans cet article la mise au point de methodes permettant de determiner la position du point principal, ainsi que la relation qui lie le point principal aux autres parametres du modele de base. On montre que l'on peut estimer la position de ce point en recourant ou non aux methodes d'autocollimation.

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The Principal Point and CCD Cameras

Close range photogrammetry and vision metrology often use signalized points in the form of active or passive targets. Many theoretical and some practical tests of different target image centering algorithms have been carried out. This paper will describe the empirical testing of several such algorithms using real data acquired for industrial measurement projects and camera calibrations. The precision and accuracy of the centering algorithms will be characterized by analysis of self calibrating network solutions using multiple camera stations and a target array. Particular emphasis will be placed on the comparison between centroiding and ellipse fitting to locate target image center.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Practical testing of the precision and accuracy of target image centering algorithms

It is common to use some form of targeting in close range photogrammetry as there are seldom enough points on the surface of an object with sufficient contrast. Targets which have been used include: light emitting diodes; black circles on a white background; retro-reflective film; projected laser beams; projected `white light' slides; feature encoded targets; and color targets. This paper discusses the characteristics of targets. In particular the established retro- reflective target and the promising projected laser target are considered as they both offer high signal-to-noise ratios together with optimum target sizes. The performance of the targets are analyzed by use of laboratory tests, for example: (1) a retro-reflective target was placed on a rotating mount with the center of the target located on the axis of rotation and the target monitored by a CCD camera under varying conditions; and (2) a laser target was analyzed by experiments which were designed to indicate the effect of speckle by moving a flat object in a direction perpendicular to the laser beam.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

T. A. Clarke

Papers

The Development of Camera Calibration Methods and Models

Comparison of some techniques for the subpixel location of discrete target images

The Principal Point and CCD Cameras

Practical testing of the precision and accuracy of target image centering algorithms

Analysis of the properties of targets used in digital close-range photogrammetric measurement