Applications of Digital Photogrammetric Methods for Preservation Documentation of Historic Homes. (2012-11)

Traditionally, conservators have relied on 2-dimensional (2D) photography to document and monitor conditions in heritage sites and objects. When a shocking, visual indicator appeared (e.g., a sudden crack in a surface), conservators took notice of what were actually thousands of slow, incremental changes (e.g., tiny fissures and failures in slowly aging materials). Conservators then photographed the area to monitor how deterioration was advancing. Two factors limit our ability to detect and monitor deterioration: our ability detect slow and small “micro” changes, and our ability to compare what humans see using 3D stereo vision to what we recorded in 2D photographs.

3D models can be made using laser scanning and 2D digital photography. For all, there are trade-offs where decisions in the workflow must be made. The finer the resolution –the smaller the area captured by either a laser point reflection or a digital camera sensor pixel – the larger the data set. In practice, the larger the object– an entire historic house or landscape versus a door or wall – the lower your resolution must be OR the more expensive and customized your computer.

This study, conducted by the Georgia O’Keeffe Museum at Georgia O’Keeffe’s historic home and studio in Abiquiu and Ghost Ranch, New Mexico,  found two 3D digital photographic technologies –RTI and Photogrammetry –change the condition-detecting and monitoring paradigm in important and beneficial ways:

• Digital 3D photo images allow us to see and measure 3D volumes and contours in ways that mimic the stereo view of a real-time human examiner.
• They allow us to use a computer to detect very small and slowly occurring changes.
• Because specular, color and texture data is digital, we can selectively highlight details, remove color data, change virtual light sources or colorize contours.
• Photography can be done by anyone with a basic knowledge of digital camera operation and a lap-top computer.
• Photography uses an ordinary, consumer-professional grade, digital camera, not expensive laser scanning equipment.
• Capture photographs are regular, open-format 2D files – RAW, TIFF and JPEG. The capture data is not a proprietary laser-scan file format.
• The user owns their own images and controls their naming, archiving, meta-data and digital management protocols.
• Assembled 3D, computational meshes, solids, and RTI images use open-source software – there are no hidden steps and every transformation of the data is documented and visible.

As part of the project, researchers documented the use of these technologies and their effort to create adoptable workflows that will result in consistent and scientifically valid results via the Georgia O’Keeffe Museum Imaging Project website.