Evaluation of accuracy of as-built 3D modeling from photos taken by handheld digital cameras

Photogrammetric methods for dense 3D surface reconstruction are increasingly available to both professional and amateur users who have requirements that span a wide variety of applications. One of the key concerns in choosing an appropriate method is to understand the achievable accuracy and how choices made within the workflow can alter that outcome. In this paper we consider accuracy in two components: the ability to generate a correctly scaled 3D model; and the ability to automatically deliver a high quality data set that provides good agreement to a reference surface. The determination of scale information is particularly important, since a network of images usually only provides angle measurements and thus leads to unscaled geometry. A solution is the introduction of known distances in object space, such as base lines between camera stations or distances between control points. In order to avoid using known object distances, the method presented in this paper exploits a calibrated stereo camera utilizing the calibrated base line information from the camera pair as an observational based geometric constraint. The method provides distance information throughout the object volume by orbiting the object. In order to test the performance of this approach, four topical surface matching methods have been investigated to determine their ability to produce accurate, dense point clouds. The methods include two versions of Semi-Global Matching as well as MicMac and Patch-based Multi-View Stereo (PMVS). These methods are implemented on a set of stereo images captured from four carefully selected objects by using (1) an off-the-shelf low cost 3D camera and (2) a pair of Nikon D700 DSLR cameras rigidly mounted in close proximity to each other. Inter-comparisons demonstrate the subtle differences between each of these permutations. The point clouds are also compared to a dataset obtained with a Nikon MMD laser scanner. Finally, the established process of achieving accurate point clouds from images and known object space distances are compared with the presented strategies. Results from the matching demonstrate that if a good imaging network is provided, using a stereo camera and bundle adjustment with geometric constraints can effectively resolve the scale. Among the strategies for dense 3D reconstruction, using the presented method for solving the scale problem and PMVS on the images captured with two DSLR cameras resulted in a dense point cloud as accurate as the Nikon laser scanner dataset.

A comparison of dense matching algorithms for scaled surface reconstruction using stereo camera rigs

Accurate measurement with photogrammetry at large sites

Large deformation measurement scheme for 3D digital image correlation method

Introduction Long bone fracture is common in traumatic osteopathic patients Good reduction is beneficial for bone healing, preventing the complications such as delayed union, nonunion, malunion, but is hard to achieve Repeated attempts during the surgery would increase the operation time, cause new damage to the fracture site and excessive exposure to radiation Robotic and navigation techniques can help improve the reduction accuracy, however, the high cost and complexity of operation have limited their clinical application Materials and methods We combined 3D printing with computer-assisted reduction technique to develop a customised external fixator with the function of fracture reduction The original CT data obtained by scanning the fracture was imported to computer for reconstructing and reducing the 3D image of the fracture, based on which the external fixator (named as Q-Fixator) was designed and then fabricated by 3D printing techniques The fracture reduction and fixation was achieved by connecting the pins inserted in the bones with the customised Q-Fixator Experiments were conducted on three fracture models to demonstrate the reduction results Results Good reduction results were obtained on all three fractured bone models, with an average rotation of 121°(±024), angulation of 184°(±028), and lateral displacement of 222 mm(±062) Conclusions A novel customised external fixator for long bone fracture reduction was readily developed using 3D printing technique The customised external fixator had the advantages of easy manipulation, accurate reduction, minimally invasion and experience-independence Future application of the customised external fixator can be extended to include the fixation function with stress adjustment and potentially optimise the fracture healing process

Dehong Yu

Papers

A cross-target-based accurate calibration method of binocular stereo systems with large-scale field-of-view

An accurate stereo vision system using cross-shaped target self-calibration method based on photogrammetry

Large field-of-view deformation measurement for transmission tower based on close-range photogrammetry

Rapid three-dimension optical deformation measurement for transmission tower with different loads