As flames ravaged the 850-year-old Notre-Dame Cathedral just days before Easter Sunday, there was little the world could do besides watch in grim horror. “Disasters such as this have a huge impact not only on those who work and worship in a church but also the wider community for whom the building is a symbol of identity,” explains Dr Kate Giles, a Senior Lecturer from the University of York’s Department of Archaeology.
The overnight destruction of one France’s most iconic landmarks—a building that took nearly 200 years to construct—provided another harrowing reminder of the fragility of cultural heritage sites around the world.
“Our heritage is much more than our collective memory. It’s our collective treasure. We owe it to our children, our grandchildren, and the generations we will never meet to keep it safe and to pass it along,” says Ben Kacyra, an Iraqi American civil engineer who founded CyArk, a nonprofit organisation dedicated to digitally recording, archiving and sharing the world’s most important cultural heritage.
Since officially launching in 2003, CyArk has documented over 200 cultural heritage sites on all seven continents, including the Sydney Opera House and Skara Brae, a 5,000-year-old stone-built Neolithic settlement in Scotland. Ben and his wife Barbara set up CyArk after witnessing the destruction of the magnificent 5th Century Bamiyan Buddhas in Afghanistan. “They were gone in an instant,” says Ben. These ancient sandstone carvings, once the tallest statues of Buddha in the world, were destroyed with dynamite by the Taliban in 2001. “Both my wife and I were so touched by this that we decided to expand the mission of our foundation to include digital heritage preservation of world sites. We called the project CyArk, which stands for Cyber Archive.”
Preserving our shared cultural heritage
Using high-resolution digital imagery and laser scan data, CyArk began working method to quickly produce accurate 3D models of cultural heritage sites that could serve as a record to aid recovery efforts in the case of natural disaster, vandalism, war or simple neglect.
Cultural Heritage can be defined as monuments, buildings, or landscapes of outstanding universal value to history, art or science. “In the beginning, CyArk worked closely with the 3D scanning community to collect data sets around the world,” says CyArk CEO and Chairman, John Ristevski. “Later we began to incorporate photogrammetry into the process using high-resolution cameras and drones to capture the colour and texture of surfaces alongside the geometry captured by the laser scanners.”
Last year on World Heritage Day, CyArk and Google Arts and Culture launched the Open Heritage initiative to provide open access to 3D cultural heritage datasets for education and research. Twenty-six high-resolution digital datasets of heritage sites were released, including Mexico’s famous Chichén Itzá, one of the seven wonders of the ancient world, and the iconic moai statues carved from volcanic stone on Easter Island.
This year, CyArk is building on the initiative even further with the Open Heritage Alliance, a collaboration with Historic Environment Scotland and the Digital Heritage and Humanities Center in the University of South Florida Libraries to release thirty-six additional datasets through Open Heritage 3D, a dedicated portal for sharing 3D cultural heritage data. The collection represents heritage from four continents and twelve different countries, spanning over five thousand years of human history.
Digitising iconic monuments
“Our goal isn’t just to digitally preserve heritage sites at risk, but to make their stories and the data we collected available to future generations of researchers, educators and students,” explains John. From an ancient city carved out of a mountain top at Mexico’s Monte Alban to isolated Expedition Huts that sheltered Shackleton and his teams in their Antarctic explorations, these datasets can be downloaded by anyone and the stories they tell touch on the diversity of the human experience as well as our shared histories. “Since we began this project last year, the data has been downloaded thousands of times, used to create 3D printed temples from Thailand and incorporated into VR experiences that let you explore an ancient city,” he adds.
To access the data, provide your name and email address after hitting the download on the relevant project page, and you will be emailed the links to download the datasets. However, be warned, the average download size per site is approximately 25GB. “There is incredible power in sharing this information with a broad community, and we can’t wait to see what they do with it.”
What is Photogrammetry?
Photogrammetry is the science of measuring physical objects and the environment using photographs. By taking overlapping photographs of the same object but from slightly varying angles, a 3D representation of that object can be obtained using a method known as ‘triangulation.’
To determine the spatial dimensions and geometry of an object using triangulation a ‘line of sight’ or ‘ray’ is drawn between the camera location and a specific point on the object. These lines are drawn on multiple photographs, with each photograph overlapping its neighbour by around 60%. When these images are superimposed, the crossing or ‘intersection’ of these rays determines the x-coordinate, y-coordinate, and a z-coordinate of the specific point of interest in three-dimensional space relative to all other point locations. A collection of these points is known as a ‘point cloud.’ A point clouds can be used to generate a 3D model of the external surface of a target object. The greater the number of points, the more accurately the object can be captured and replicated. This process is also referred to as ‘3D stereophotogrammetry’.
150 Years of Photogrammetry
The expression ‘photogrammetry’ was first used by the Prussian architect Albrecht Meydenbauer in the Berlin Architectural Society, Weekly Journal in 1867. Albrecht was experimenting with photographic images as a cost-effective means to store detailed information about monuments and historic buildings. He aimed to create a national ‘Cultural Heritage Archive’ that would enable objects of importance to be accurately reconstructed if damaged or destroyed.
By taking indirect measurements of these structures on photographic images, Albrecht believed he could replace the expensive and often dangerous task of measuring buildings and monuments directly. However, it would take him more than 25 years to develop the methods and instruments necessary to realise this idea.
During his initial experiments, Albrecht believed that any camera could be used for photogrammetry, but it quickly became apparent that a purpose-built system would produce much better results. The first of Albrecht’s photogrammetric systems combined a measuring instrument and photographic camera into a single device. This new camera was equipped with a Pantoskop wide-angle lens (with a fixed focal length of 25 cm) and captured 30 x 30 cm images onto glass plates. Crosshairs were added to each image during exposure to form a simple coordinate system, and the camera itself was mounted to a tripod, which enabled highly accurate horizontal adjustments to the camera and image coordinate axis, as well as the vertical image plane.
With this new instrument, Albrecht performed practical tests in the town of Freyburg-on-Unstrut, which sits just over 100 miles southwest of Berlin. Here, he recorded metric images from the town church as well as a section of terrain for topographic purposes. Thankfully, Albrecht’s experiment was a success and enabled him to secure valuable evidence on the suitability of photogrammetry for both architectural surveys and topographical mapping.
Having silenced his critics, Albrecht founded the Royal Prussian Photogrammetric Institute in 1885, which became the first photogrammetric institution in the world for the documentation of cultural heritage. Between 1885 and 1920, the institution recorded over 2,600 objects in approximately 20,000 photogrammetric images.
Preserving Cultural Heritage
Fast-forward over 130 years and CyArk has replaced Albrecht’s early photogrammetric camera and tripod with a Nikon D810 digital SLR and GigaPan Epic Pro robotic camera mount to form a vastly updated version of the original 19th-century system. The nonprofit also makes use of a DJI Phantom 4 Pro in ‘Point of Interest’ mode to capture overlapping photos of roofs and other areas that are impossible or too fragile to document from the ground.
CyArk’s team has also been developing a low-cost heritage documentation kit, which includes a digital camera, laser rangefinder, tablet computer, GPS receiver, compact tripod and video tutorials on how to digitally document a site.
“A key component of the kit was its use of off-the-shelf components that could be easily obtained by anyone and the methods and take-away resources that can easily be adopted and referenced in the field,” explains CyArk’s Heritage Program Manager, Kacey Hadick.
At under £1,200, this relatively inexpensive solution relies on advances in photogrammetry software combined with laser distance measurements to quickly and accurately document heritage sites while requiring only moderate technical ability from the operator.
Digital Documentation Tools
Photogrammetry images are shot as bracketed HDR to capture details in both light and dark areas. Three photos are taken, one using the camera’s recommended settings, one intentionally underexposed, and one intentionally overexposed. The resulting images are then processed using Lightroom, XRite, and Photomatix software before RealityCapture automatically extracts 3D models from the images. The result is an incredibly complex digital model with a hyper-realistic photographic texture.
“These techniques can often result in significant time and cost savings compared to traditional survey methods, and provide a much more accurate and more detailed record of the site,” adds CyArk CEO and Chairman, John Ristevski.
What is LiDAR?
LiDAR stands for Light Detection and Ranging. It describes the process of rapidly firing pulses of laser light at a solid surface to measure its distance from the laser source. By calculating the time it takes for light from each pulse to return, the distance of the target surface can be measured within fractions of a millimetre.
The formula used to calculate how far a light photon has travelled to reach the object or target surface is relatively simple. Multiply the speed of light by the time it takes for the laser light to return to the LiDAR sensor (known as ‘time of flight’) and then divide that number by two.
The raw data collected by LiDAR sensors typically contain millions of measurements and produces a much denser point cloud than those collected using traditional photogrammetry techniques. These high-density point clouds enable not just the distance of the object to be determined but its size and shape as well.
Fire the laser!
“3D scanning is growing within the Heritage field as an acceptable standard for site documentation,” says Justin Barton, Chair of CyArk’s Technology Center Advisory Board. “3D laser scan data can easily be converted to CAD and other imaging programs for conservation, management, and restoration works as well as virtual tourism, education, and information dissemination.”
The term LiDAR was first introduced by William Middleton and Athelstan Spilhaus in 1953 to describe attempts made by the Bureau of Intelligence and Research in the United States to measure cloud base heights using pulses of light in the late 1930s. However, the rapid development of modern LiDAR technology would not begin until the first laser was built in 1960 by Theodore Maiman at Hughes Research Laboratories in California. A decade later, early LiDAR systems used to successfully measure lunar surface height and topography during the Apollo 15 mission in 1971, piquing global public interest in this exciting new technology.
Today, CyArk uses LiDAR to document and record a large variety of objects, structures, buildings, and topographies. Everything from small archaeological finds to vast geo-referenced landscapes. Making this data viewable on the Web is at the heart of CyArk’s mission. The Internet archive houses the media collected from each of its projects, providing free access to all project data. “The mystery of what utility people might find in the data is part of the excitement,” says John Ristevski. “Some of the exciting frontiers are in virtual reality and augmented reality, and we are excited to see what type of experiences people can build around heritage data.”
To find out more about CyArk’s work and to explore their vast online archive of heritage data, visit https://cyark.org/.
Try it yourself
If you’re interested in quickly creating 3D models from images captured on your digital camera, we suggest trying the ‘ARC 3D webservice’ by the University of Leuven in Belgium. After registering, upload your images to their server and the 3D spatial data will be extracted and emailed to you automatically. For more information visit: http://bit.ly/ARC3D-webservice
Image credits: CyArk & Partners