3D scanning a one-piece dinosaur skeleton in minute detail

A 1:1 scale 3D printed replica of Colorado’s State Symbol, the Kessler Stegosaurus, has been created for a local museum with the help of Artec Spider 3D scanner.

One of the most iconic scenes depicted in a dinosaur exhibit has to be the Stegosaurus and Allosaurus facing off in the Denver Museum of Nature & Science. The 26-foot-long Stegosaurus represents Colorado’s State Dinosaur. Not just the species of dinosaur, but the individual specimen that was adopted to represent the state. Stegosaurus was a herbivorous dinosaur weighing up to 10 tons that inhabited the area now called Colorado 150 million years ago. What makes this particular Stegosaurus so special is not the fact that it was found in Cañon City, Colorado, or even that it was mostly complete, a very rare thing for dinosaur skeletons. It was found by a class of high school students on a fossil-hunting field trip in 1936, and the teacher of that class of students, Frederick Carl Kessler, was able to arrange for his students to work alongside professional paleontologists to excavate the fossil skeleton.

The Stegosaurus (right) and the Allosaurus on display at the Denver Museum of Nature & Science

Enter Mike Triebold of Triebold Paleontology, Inc. (TPI) in Woodland Park, Colorado. TPI restores and mounts fossil skeletons and creates skeleton casts, supplying them to museums across the globe. The company’s clients include the American Museum of Natural History in New York, Carnegie Museum in Pittsburgh, and the Smithsonian Museum of Natural History in Washington, D.C. The TPI headquarters house a collection of casts and original fossil specimens, which are on exhibit at the company’s hands-on natural history museum, the Rocky Mountain Dinosaur Resource Center.

Mike Triebold was looking to add a Stegosaurus to his catalog of casts, but not just any Stegosaurus. He was focused on getting the famous Kessler Stegosaurus at the Denver Museum for the project if at all possible because the new Royal Gorge Dinosaur Experience in Canon City was being built and they wanted a copy of the Stegosaurus that was collected by Kessler near Canon City.  RGDE owner Zach Reynolds’ grandfather regularly accompanied Kessler on dinosaur digs from the 40s through the 60s, so the Stegosaurus has both family and community ties.

Discussions ensued and with the Denver Museum’s blessing, the work began.

Reproducing this specimen was complicated by a couple of factors. One is the size of the specimen. Not only is this dinosaur over 26 feet long, but with the tall plates lining its neck, back and tail, it is also over 9 feet tall. Normally the size would not be an insurmountable challenge as each individual bone would just be molded in silicone and cast from liquid plastics. This specimen is not just bones on shelves though. It was mounted and placed on exhibit in the 1990s using purely permanent means, so it was not built to ever be taken apart. Steel was shaped around the skeleton, welded in place, and permanently puttied to the bones, so molding the individual bones in silicone was rendered impossible.

To recreate this specimen TPI’s Matt Christopher needed to mold it using 3D scanning. “We needed to three-dimensionally digitize the skeleton that could not be dismantled so that a replica could be 3D printed,” says Matt. “The dimensions and surface details needed to be close enough to what we would get from a silicone mold so that we could hand-finish 3D prints to look exactly like the original specimen.”

TPI used Artec Spider structured-light 3D scanner along with Artec Studio 3D scanning and processing software for the job. The scanner was supplied by Artec’s local partner 3D Printing Colorado. “Our Artec Spider captured exactly what we needed,” says Matt.

The final model of the Kessler Stegosaurus in Artec Studio, side view

Spider was used to scan individual bones and regions of the skeleton as individual projects in Artec Studio. “This involved crawling inside the rib cage (yes, a full-grown person fits inside the rib cage of Stegosaurus) to capture the dorsal vertebrae forming the dinosaur’s back and the medial surfaces of the rib cage, shoulder blades, and hips,” says Matt. “There were also some interesting poses taken atop a step ladder to reach the tops of the big fan-shaped plates on the dinosaur’s back. We were able to capture all of the elements we needed, from the tip of the nose to the huge spikes at the end of the tail.”

The team ended up with 629 individual scans across 71 individual scan projects in Artec Studio. The number could have been higher, but in order to save time it was decided to skip scanning the elements that could be mirror-imaged to generate the other side, like the arms, legs and ribs.

Each scan needed to be aligned, cropped, and converted to 3D mesh files in Artec Studio. “The alignment features in Artec Studio were absolutely paramount to the success of this project,” says Matt. “Aligning each scan was as simple as manually orienting to a loose approximation of the correct position and letting the alignment tool refine the fit to perfection. Using Artec Studio to create and control the mesh generated from the aligned scans allowed us to extract the exact level of detail we wanted for manipulating and 3D printing.”

Exported meshes were free of artifacts thanks to a filter in Artec Studio that removes all elements smaller than the master scan. Small holes were automatically filled using the hole filling algorithm in Artec Studio. “Had we been scanning individual, unmounted bones, it would have been easy to generate complete, watertight meshes directly out of Artec Studio that would have required no additional post processing” says Matt. “With the steel armature remaining to be removed and the obstructed surfaces left to be reconstructed, watertight meshes were not really an option or a necessity for remaking the Stegosaurus.”

The resulting meshes were imported into ZBrush for separation of articulated elements, reconstruction of surfaces that were impossible to reach with the 3D scanner, like the spaces between articulated bones, and removal of the steel armature that obscured some bone surfaces.

The final model of the Kessler Stegosaurus in Artec Studio, front view

TPI has a variety of 3D printers at their disposal ranging from a small Formlabs Form2 SLA desktop unit to a large-format Atlas from Titan Robotics. With numerous printers working on the project, printing the skeleton required six months. As the prints were finished, they were lightly resurfaced by hand and prepared for molding by adding mockups for internal steel armature and articulating some specimens to be molded in sections rather than as individual bones. Each completed bone or assembly is called a master. These masters were then molded in silicone rubber using high quality liquid silicone rubbers in two-part to multiple-part molds; something TPI staff has been doing for nearly 30 years.

The finished molds were then fitted with internal steel to be surrounded by plastic resins in the casting process. “The plastic is poured around the steel, so no external armature that would hide bone surfaces is needed,” says Mike. “With the casts poured around the armature, we can assemble the skeleton in any one of an infinite number of poses and weld together the steel protruding from inside each plastic cast. The mounted skeleton is then ready for hand-painting and delivery.”

With the project now completed, it will be on permanent display at the Royal Gorge Dinosaur Experience (  www.dinoxp.com ) in Canon City, Colorado, being unveiled on Saturday, May 19th. Zach Reynolds, his family and dad Dave will now be able to share the fulfilment of this important wish with the public for years to come.

According to Mike, this project would have been impossible to complete a couple of decades ago. “With our Artec Spider we were able to marry the best technologies of today with the most advanced traditional methods of molding and casting to create an exact copy of that great dinosaur without even touching it,” he says. “Now, how about that Allosaurus…”

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