Scanning Photogrammetry for Measuring Large Targets in Close Range

Shan Huang,Xuan Xu,Min Tang,Zuxun Zhang,Tao Ke

doi:10.3390/rs70810042

Abstract

In close-range photogrammetry, images are difficult to acquire and organize primarily because of the limited field of view (FOV) of digital cameras when long focal lenses are used to measure large targets. To overcome this problem, we apply a scanning photography method that acquires images by rotating the camera in both horizontal and vertical directions at one station. This approach not only enlarges the FOV of each station but also ensures that all stations are distributed in order without coverage gap. We also conduct a modified triangulation according to the traits of the data overlapping among images from the same station to avoid matching all images with one another. This algorithm synthesizes the images acquired from the same station into synthetic images, which are then used to generate a free network. Consequently, we solve the exterior orientation elements of each original camera image in the free network and perform image matching among original images to obtain tie points. Finally, all original images are combined in self-calibration bundle adjustment with control points. The feasibility and precision of the proposed method are validated by testing it on two fields using 300 and 600 mm lenses. The results confirm that even with a small amount of control points, the developed scanning photogrammetry can steadily achieve millimeter scale accuracy at distances ranging from 40 m to 250 m.

Highlights

The development of electric sensors and image processing techniques has contributed to the rapid growth of the application of photogrammetry
Three kinds of image matching exist in this process: one for synthetic images, one for original images from different stations, and one for original images from the same station
We conduct several groups of comparative experiments to evaluate the effects of different factors, such as photo distance, overlapping rate between original images in image matrices, given number of least stations (M)from which any interest point on the target are acquired, set intersection angle(θ), and focal length, on the measurement accuracy in scanning photogrammetry

Summary

Introduction

The development of electric sensors and image processing techniques has contributed to the rapid growth of the application of photogrammetry. Since 2000, photogrammetric mapping using digital photographic systems has become popular because of the application of digital cameras [1,2,3,4,5,6] Given their changeable focus lens, various photography methods, and low cost, digital single-lens reflex cameras (DSLRs) are widely applied in close-range measurement tasks [7,8,9,10,11,12,13]. In many measurement methods, multi-view photography is applied to solve this contradiction [19,20,21] This technique introduces new problems, such as the difficult acquisition of images in order, in large measurement ranges. There is a lot of work to be done to solve these issues

Results

Discussion

Conclusion