Page 13 .... Cherub Statue, https://skfb.ly/CMIG (accessed Feb 17, 2017). 3DFlowb. 3DF Zephyr Photography ... sgmccann.pdf (accessed Feb 14, 2017). nVidia.
APPLICATION OF SfM-MVS PHOTOGRAMMETRY IN GEOLOGY VIRTUAL FIELD TRIPS Youngwoo Cho and Renee, M. Clary
OBJECTIVES Research a procedure for reconstructing 3D models of geologic targets for Virtual Field Trips (VFTs) using Structure from Motion (SfM) and Multi-View Stereo (MVS) Photogrammetry. Research techniques for achieving high enough quality of the models for VFTs, based on the photography and post-production techniques.
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INTRODUCTION: 3D Models The product of a mathematical representation of an object using surface features of that object.
WikiVisually
3D FLOWa
INTRODUCTION: SfM-MVS SfM-MVS; Structure from Motion – Multi-View Stereo Point Cloud Data Acquisition SfM is the process to calculate a sparse 3D point cloud model from the overlapping pictures taken for the surface of an object from different camera locations. (Carrivick et al. 2016)
INTRODUCTION: SfM-MVS SfM-MVS; Structure from Motion – Multi-View Stereo MVS is a refinement of 3D model from the SfM method. Algorithms based on the measurement of a consistency function are used to generate a dense 3D reconstruction of an object. (McCann) Limitations given by noise and calibration errors, in terms of colors and texture. (McCann)
PROBLEM DESCRIPTION Problems in taking pictures of geologic targets, in terms of reconstruction quality. Geologic outcrop Under the Sun 1. High-contrast, Shadows, Time-variant 2. Too large to control the photographic environment.
PROBLEM DESCRIPTION Small geologic samples Uniform lighting Dealing with shadows and glossy surface
METHODS: PHOTOGRAPHY Lighting Considerations Geologic outcrop: Low-Contrast Environment Cloud covers Early morning or late afternoon shots Canopy Limited use of camera flash Small geologic samples Dealing with shiny or bright spots Diffusers Polarizers
METHODS: PHOTOGRAPHY Dynamic Range Considerations High Dynamic Range Photography
Johnston
METHODS: PHOTOGRAPHY Dynamic Range Considerations High Dynamic Range Photography Auto Exposure Bracketing
METHODS: PHOTOGRAPHY Dynamic Range Considerations High Dynamic Range Photography High dynamic range blending
METHODS: PHOTOGRAPHY Dynamic Range Considerations Low ISO shooting RAW capture
METHODS: PHOTOGRAPHY RAW capture Higher dynamic range Lower noise
Photography course
METHODS: PHOTOGRAPHY Field-of-Depth Considerations Field of Depth consideration Focus stacking Small aperture photography Stable support for long exposures Tripods or Jibs Shock Damping
Professional Photography Simplified
METHODS: PHOTOGRAPHY Noise Suppression Low ISO Sufficient illumination Dealing with shadows while shooting RAW image capture (High Dynamic Range, low noise) Reasonable noise sampling and application
METHODS: PHOTOGRAPHY Considerations for Photographic Equipment Cameras Sufficient sensor size Good noise suppression Good dynamic range RAW capture capability Image stabilizer Mirror lock-up
METHODS: PHOTOGRAPHY Considerations for Photographic Equipment Lenses Low geometric distortion No wide-angle lenses Large maximum-aperture Good optical quality
METHODS: PHOTOGRAPHY Considerations for Photographic Equipment Accessories Heavy-duty tripod with low- to high-angle capture Portable Jimmy Jibs or Cranes Cable release or WIFI/Bluetooth Shooting Camera flash Diffuser, Bouncer, or Reflection plate
METHODS: PHOTOGRAPHY Cameras used Canon 5D Mark II
Canon 350D
Sufficient sensor size
21.1 MP
8 MP
Good noise suppression
100-6400
100-1600
Good dynamic range
△
×
RAW capture capability
○
○
Image stabilizer
×
×
Mirror lock-up
○
○
METHODS: PHOTOGRAPHY Cameras used Canon 5D Mark II
Canon 5D Mark IV
Sufficient sensor size
21.1 MP
30.1 MP
Good noise suppression
100-6400
100-32000
Good dynamic range
△
○
RAW capture capability
○
○
Image stabilizer
×
×
Mirror lock-up
○
○
METHODS: PHOTOGRAPHY Lenses used Canon 24mm f/1.4 L II
Canon 70-200mm f/2.8 L
Low geometric distortion
○
○
No wide-angle lenses
△
○
Large maximumaperture
○
○
Good optical quality
○
○
METHODS: PHOTOGRAPHY Cameras and Lenses used
METHODS: PHOTOGRAPHY Accessories used Heavy-duty tripod with low- to high-angle capture Manfroto 055X PROB with 410 Gear Head Cable release
○
Camera flash
×
Diffuser or Reflection plate ○
METHODS: RECONSTRUCTION Constructing 3D models of objects for VFTs Building Sparse Point Clouds Building Dense Point Clouds Building Mesh Building Texture
METHODS: COMPUTING SYSTEM CPU: Intel Core i7-4790 CPU @3.60 GHz RAM: 32.0 GB Video Card: nVidia Geforce GTX 1060 6GB CUDA: “A parallel computing platform and application programming interface (API) model created by Nvidia. It enables dramatic increases in computing performance by harnessing the power of the graphics processing unit (GPU).” (nVidia)
RESULTS Small geologic samples Geode
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RESULTS Small geologic samples Geode
RESULTS Small geologic samples Shark Tooth fossil
RESULTS Geologic outcrops Petrified wood
RESULTS Geologic outcrops Smith County
RESULTS Geologic outcrops Smith County
RESULTS Geologic outcrops Smith County
CONCLUSION Photographic techniques enhanced the quality of the 3D model, unless otherwise fail to do or generates weird results. High dynamic range photography and noise suppression helps decrease the photographic and reconstruction noise. Good selection of photographic equipment is very important.
CONCLUSION Lighting control is important for the reconstruction of the small geologic samples, particularly for that having glossy surface. It is also very important in outcrop shooting although it is sometimes not easy to control. Choosing a cloudy day, early morning or late afternoon for outcrop shooting helps reduce the lighting contrast. But the weather can not be controlled and early-morning/late-afternoon shooting gives an additional challenge due to the sunlight coming into the field-of-view.
CONCLUSION Using camera flash is a good choice to decrease the contrast in the field, but it sometimes may cast additional shadow. It also has a limitation in the case the outcrop is very large. RAW capture is not an option. Need to keep the camera stable during a long exposure with large f-ratio. A plan for additional stability is an option. Need to suppress the photographic noise as low as possible.
CONCLUSION Field of Depth should be large enough to have all points in the image be well focused. The f-ratio of 22 or larger was used. Focus stacking could be an alternative. Reconstructing a 3D model could take very long time, especially in case of large number of pictures and higher precision settings in the software, often more than a week. So, having a higher performance computer is vital. Need to choose a good graphics card with a good CUDA performance.
DISCUSSION (COST) It requires good photographic equipment to build 3D models to be used in VFTs, though it is still cheaper compared to the other point cloud data acquisition method. (COMPUTING TIME) It takes a substantial amount of time to build a 3D model; a factor increasing the cost of this method. (SOFTWARE PERFORMANCE) It still looks a long way to go, especially in the software performance.
REFERENCES 3DFlowa. Cherub Statue, https://skfb.ly/CMIG (accessed Feb 17, 2017) 3DFlowb. 3DF Zephyr Photography guide, http://www.3dflow.net/technology/documents/photogrammetry-how-to-acquirepictures/ (accessed Feb 17, 2017) Agisoft (2016). Agisoft Photoscan User Manuals, http://www.agisoft.com/downloads/user-manuals/ (accessed Feb 14, 2017) Carrivick, J.L., Smith, M.W., Quincey, D.J. (2016). Structure from Motion in the Geosciences (Analytical Methods in Earth and Environmental Science), Wiley. Kindle Edition. Johnston, M. More on Dynamic Range, http://theonlinephotographer.typepad.com/the_online_photographer/2009/02/dyna mic-range.html (accessed Feb 20, 2017) LuptidStyle.com. Professional Photography Simplified, http://luptidstyle.com/professional-photography-simplified/ (accessed Feb 21, 2017)
REFERENCES McCann, S. 3D Reconstruction from Multiple Images, https://web.stanford.edu/class/cs231a/prev_projects/CS231a-FinalReportsgmccann.pdf (accessed Feb 14, 2017) nVidia. What is CUDA?, https://www.nvidia.com/object/cuda_home_new.html (accessed Feb 21, 2017) Photography course. RAW vs JPG, http://photographycourse.net/raw-vs-jpeg/ (accessed Feb 21, 2017) WikiVisually.com. Structure from Motion, http://wikivisually.com/wiki/Structure_from_motion (accessed Feb 21, 2017)
