Cultural Heritage Imaging


Recovering Traditional Weaving Knowledge: Te Rā, The Māori Sail by cdschroer
October 28, 2020, 7:31 am
Filed under: 3D, Equipment, Lighting, On Location, photogrammetry, RTI | Tags: , , ,

In January 2020 Mark Mudge and I traveled to the British Museum in London to document the only existing Māori canoe sail of its kind, made over 200 years ago. The imaging work was performed in collaboration with the New Zealand project Te Rā – The Māori Sail Whakaarahia anō te rā kaihau! – Raise up again billowing sail! funded by The Royal Society – Te Apārangi Marsden Fund.

The New Zealand team produced a 13½-minute video of the project that you can watch here: Imaging Te Rā at the British Museum 2020

Kira Zumkley, London based heritage photographer and CHI volunteer,
helps prepare the sail for imaging

The construction and materials of the last known Māori sail, Te Rā, had not been identified, documented, or made publicly available, until this project put significant efforts into these identifications and documentation. Māori textile researchers from New Zealand brought in CHI to image the sail, which is made with fragile plant materials and feathers. The CHI team used both photogrammetry and Reflectance Transformation Imaging (RTI) to help the experts examine and understand more about the delicately woven and perishable materials. The research team wanted to gain a greater understanding of how the Māori sailed the ocean and the intricacies of their weaving techniques.

We worked with the sail on site at the British Museum for 5 days.

The first day was all preparation: meeting the team, examining the sail, setting up equipment, testing lights, and troubleshooting. The second day was spent on the imaging. The initial preparation had begun back in the CHI studio in San Francisco, when Marlin Lum, Imaging Director, prepared for the intensive imaging project by creating a life-size paper template of the sail so the CHI team could work out the imaging logistics ahead of time. Marlin had also created an ingenious camera rig to manage the imaging and protect the fragile materials. Marlin’s rig was attached to a rental pro video slider unit that we picked up in London on the first morning.

Mockup of the sail at the CHI studio in San Francisco with custom-built camera rig

At the museum collection facility, the sail was spread out on a protective foam core platform on the floor, covered by black paper.  Because the sail has a pattern of holes in it, we performed tests on how best to mask out the holes so that they would be correctly modeled as holes in the final model.  The black paper worked best. Over this the team positioned the trolley with its cantilevered arm that could move across and incrementally shoot the entire area, photo by photo. The camera height could be adjusted using a slider and the camera angle could be adjusted using a ball head.

Here is my project note from the morning of the second day:

“Light tests and light adjustments are done. We add a Speedlite to the mix of lights to deal with a corner that was a bit dark. We will trigger the Speedlite (Michael’s Canon 600) with the PocketWizard TT1 and TT5 combo and all 4 Monoblocks are set to slave mode. It takes a bit of time to tune everything in using the light meter and small adjustments. We feel now the entire sail is evenly lit and imaging can begin.”

Scale bars were placed around the small end of the sail as were color checkers. Using a Canon 5DSR with 24mm f2.8 IS USM lens, and shooting at 18 inches distance from the subject, the imaging began with a calibration pass with 90-landscape-270 rows – then returned to the 90 position for the remainder of the imaging in that pass.

The feathers that trim the sail presented a significant imaging challenge: they stick up, and there are knots and places where the material juts out. The camera focus was set manually to allow some extra depth of field above where the main body of the sail was laid out, so that these elements would remain in focus.

As the work progressed, I recorded this:

“We completed the second pass of the sail with a 50mm lens today and shot 3 RTIs of detail areas chosen by Donna from the Maori textile team. Then we had a crew come in to turn the sail over, and we prepped everything for the back side (which is actually more important for the weavers). We will begin shooting that first thing tomorrow.”

Detail of a “hiki” or join of two panels from RTI with mathematical enhancement.
Image: © TeRa Project, Marsden Fund, 2020:

After completing the work on site each day, we returned to our London apartment and began the next step: processing the images of the sail. We have built the RTIs and some other high-resolution 2D outputs of the sail and shared them with the team. The detail is fantastic. We look forward to the team’s continued research and the publishing of their findings, along with our imaging results.

Detail of the front of the sail from an Orthomosaic created using photogrammetry. Each pixel in the image represents 0.049mm – essentially 5/100s of a mm on the surface of the sail. Image: © TeRa Project, Marsden Fund, 2020

Special thanks to: Donna Campbell, co-Principle Investigator (co-PI) for the research project worked closely with us on site; Julie Adams, Curator of the Oceania Collections at the British Museum, hosted the imaging project; Michael O’Neill, a photographer from the National Museum of New Zealand Te Papa Tongarewa; Kira Zumkley, a London-based heritage photographer and researcher; and Jill Hassell, museum assistant. Catherine Smith, co-PI on the project aided in logistics and overall project management.

You can read more about the sail in the research team’s blog and also the British Museum’s description of the sail from its online collection.


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