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A Structure from Motion photogrammetry-based method to generate sub-millimetre resolution Digital Elevation Models for investigating rock breakdown features

Preprint published in 2018 by Ankit K. Verma, Mary C. Bourke
This paper is available in a repository.
This paper is available in a repository.

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Preprint: policy unknown
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Postprint: policy unknown
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Published version: policy unknown

Abstract

We have generated sub-millimetre resolution DEMs of weathered rock surfaces using SfM photogrammetry techniques. We apply a close-range Structure from Motion (SfM) photogrammetry-based method in the field and use it to generate high-resolution topographic data for weathered boulders and bedrock. The method was pilot tested on extensively weathered Triassic Moenkopi Sandstone outcrops near Meteor Crater in Arizona. Images were taken in the field using a consumer grade DSLR camera and were processed in commercially available software Agisoft Photoscan to build dense point cloud. Dense point clouds were registered to a local 3D coordinate system (x, y, z) which was developed using a specially designed triangle coded control target and then exported as Digital Elevation Models (DEMs). The accuracy of the DEMs was validated under controlled experimental conditions. A number of checkpoints were used to calculate errors. We also evaluated the effects of image and camera parameters on the accuracy of our DEMs. We report a horizontal error of 0.5 mm and vertical error of 0.3 mm in our experiments. Our approach provides a low-cost method, for obtaining very high-resolution topographic data on weathered rock surfaces (area < 10 m 2 ). The results from our case study confirm the efficacy of the method at this scale and show that the data acquisition equipment is sufficiently robust and portable. This is particularly important for field conditions in remote locations or steep terrain where portable and efficient methods are required.

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