Capturing Large-Scale Artifacts via Reflectance Transformation Imaging with a Drone

Demonstration

Friday, April 03, 2020: 12:45pm - 1:45pm -

Montana Fowler, University of California, Santa Cruz, USA, James Davis, UC Santa Cruz, USA, Angus G. Forbes, University of California, Santa Cruz, USA

Archeologists capture artifacts with Reflectance Transformation Imaging (RTI) to gather detailed information about an object’s surface that cannot be viewed with a photograph or the naked eye. RTI, also known as Polynomial Texture Mapping, was originally introduced to model self-shadowing and interreflections on textures [Malzbender 2001]. Unfortunately, the process of placing the lights in a dome formation over the object can be quite tedious and limits the size of objects that can be captured. In our approach, we use a consumer drone to hold the lights in position to collect RTI for large artifacts, replacing previous approaches such as the string method [CHI 2013] and the dome of lights method [Piquette 2011].

Many drones have lighting mounts available for users to illuminate scenes for photography, videography, and safety, but to our best knowledge, these mounts have never been used for holding and placing light for RTI. Hepp et al. capture 3D scans of buildings with a quadcopter holding an RGB camera, demonstrating the capability for drones to gather information for objects as large as buildings [Hepp 2018]. In our work, we use a drone to carry and position the light needed for assembling RTI.

To validate our approach, we used a drone to collect data on a vase whose face had a 32in diagonal, much larger than the 9in diagonal limit imposed by a dome with a diameter of 1m [Piquette 2011]. Our approach also works in outdoor environments. We successfully captured RTI outside on the Santa Cruz Surfer Memorial Statue, concentrating the imaging on the figure of the surfer, which has a 6ft diagonal. Flying a drone requires some practice, and outdoor capturing needs to take place at night in order for the drone’s light to have an effect on the surface of the object. Despite these minor caveats, our work introduces an effective way for archeologists and other cultural heritage researchers to quickly and easily collect images of large objects for RTI with a drone.

Bibliography:
[CHI 2013] Cultural Heritage Imaging. Reflectance transformation imaging: Guide
to highlight image capture. 2013. Available online at: http://culturalheritageimaging.org/What_We_Offer/Downloads/

[Hepp 2018] Benjamin Hepp, Matthias Nießner, and Otmar Hilliges. Plan3d: Viewpoint and trajectory optimization for aerial multi-view stereo reconstruction. ACM Transactions on Graphics, 38(1):1–17, 2018.

[Malzbender 2001] Tom Malzbender, Dan Gelb, and Hans Wolters. Polynomial texture
maps. Proceedings of the 28th Conference on Computer Graphics and Interactive Techniques (SIGGRAPH), pages 519-528, 2001.

[Miles 2014] James Miles, Mike Pitts, Hembo Pagi, and Graeme Earl. New applications of photogrammetry and reflectance transformation imaging to an Easter Island statue. Antiquity, 88(340):596–605, 2014.

[Piquette 2011] Katheryn E Piquette. Reflectance transformation imaging (RTI) and
ancient Egyptian material culture. Damqatum: The CEHAO newsletter – El boletín de noticias del CEHAO 7, 2011.

Drone RTI Project Website: https://montanafowler.github.io/website/rti_drone_project.html

Drone RTI Project Video: https://www.youtube.com/watch?v=KCjwG_RqmhY&feature=youtu.be