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3D printing of scalable reproductions from laser scan data is emerging as a powerful method of support for historical preservation projects. This article will provide a detailed look at the workflow required to produce a scale model for an important historical site in Alberta, Canada.
The Turner Valley Gas Plant was associated with western Canada’s largest, most productive oil field until the late 1940’s. Located in Turner Valley on the Sheep River, it is 60 kilometers southwest of Calgary, Alberta, Canada. The plant site was used for natural gas production and refining from 1913 until it was decommissioned in 1985. The Turner Valley Gas Plant became an Alberta Provincial Historic Resource in 1988 and a Canadian National Historic Site in 1995.
During the life of the plant upgrades were constantly taking place. By 1921, Royalite Oil Company had built a compressor station on the site and a pipeline to tie into Calgary’s supply systems. The 1924 Royalite No. 4 wellone of the field’s largest producersblew in from a sour gas zone. High well flows required new separators to recover gasoline and scrubbers to remove hydrogen sulfide (H2S)a toxic and corrosive component in sour gas. In 1952, sulfur extraction was added. The plant scrubbed gas and produced gasoline, propane, and sulfur.
The conservation of this sulfur plant required thorough and exacting documentation. Laser scanning was recognized as a suitable tool for documenting the complex arrangement of historical features and equipment, including vessels, tanks, walkways and piping.
The laser scan point cloud provides the precise position of all aerial pipe runs and storage vessels in 3D space. Since the complex was scanned with a Faro Focus 3D, it was possible to deliver the scans using a WebShare 2Go USB drive. This provided Historic Resources Management Branch staff with HD panoramas from each of the 17 scan positions. Panoramas captured from ground positions, catwalks and from the overhead tank give HD views of the equipment in its original placement from many angles. The WebShare 2Go measurement feature will assist placement of the reconditioned equipment to its original position. Sectioning the point cloud in increments above ground level gives exact placements of vessels, piers and towers. If more eBIM modeling is needed, the point cloud is importable to CAD software.
A scale model of the plant with its configuration of vessels and pipes was desired for visual reference. This meant reviewing the upload limits of online 3D print providers, print dimensions and pricing formulas. The provider’s printer had a 100MB file limit and priced the physical model based on the volume of polyamide used in the 3D print.
Several considerations were needed for creating a printable mesh. Details needed to be meshed quickly since the 13,000 square foot site had a massive point count. Due to the file size limit, the mesh needed to retain detail after decimation. To reduce costs, the meshing software needed to create hollow spaces inside the tanks and walls.
Since the plant interior was scanned and registered into the overall point cloud, interior walls, beams and some of the interior boilers were nested in the point cloud file for meshing. The meshing software needed to produce double-sided wall surfaces. 3D MobileScan had used Thinkbox Frost to produce meshes. Frost has origins in particle effects in film. The speedy rendering and realistic final mesh makes it valuable in meshing point clouds. The radius around particles is controllablesmaller radii create more defined features. Frost delivered the hollow spaces, two sided walls and excellent detail to the mesh even after decimation.
Since Frost is a 3ds Max plug-in, 3ds Max needs to be installed. Frost, as a 3ds Max plug-in, exported the poly heavy mesh as an STL that was decimated to 10% of its original size using a quadratic filter. This produced a working mesh that had no loss of detail but was faster for postproduction work and met the upload limits of the 3D print service provider.
Finalizing the mesh for printing involved using a sculpting program to remove holes in the mesh due to laser shadows. Volume brushes extended surfaces where occlusions occurred and removed holes. Mesh programs will artifact in areas where point cloud information is noisy or incomplete. Frost meshes sparse areas well, but occasionally artifacts such as small bumps occur in noisy areas. These were corrected with smoothing brushes without losing surface details.
On upload of the 3D print STL, the print service provider checked the walls of the model for adequate thickness and then thickened the base while retaining the slope of the work yard that was captured in the Frost mesh. To scale at 100:1, the final 3D print was dimensioned at 15" x 13" x 5"which meant a 2 week wait time for the printers with the largest print envelope.
The scale model gives Historic Resources Management Branch, Alberta Culture a reference to configure the yard exactly as it existed historically. The existing pipes and tanks will be removed from the work yard and reconditioned.
The mesh model makes it possible for elements that break apart due to corrosion to be recreated by a CNC machine. As the restored equipment is reinstalled in the yard, it can be returned to its original place, since the model shows the original footprint, placements and orientations.
The model also helps in evaluating ideas for enhancing the visitor experiencesuch as using a continuous ramp for interior equipment views and views of the yard. The 3D model allows design mockups to be tested quickly.
The speed and surface building accuracy of Frost opens eBIM possibilities for modeling reality. Modeling techniques that are based on extrusion of sections are more approximate. The information in a surface mesh represents conditions that exist in a building. These conditions could include out of square/ out of plumb walls, and uneven walls and floors. Detailing can be presented. The speed and accuracy of Frost has the potential to bring instantaneous eBIM modeling of a registered point cloud using PTS or XYZ formats as mesh sources.
Export of surfaces as an STL makes milling to life-size dimensions possibleusing the xyz surface map for 4-axis router tool paths. Milling the negative of the surface produces a mold.
The workflow leading to the 3D print can be applied to a wide range of restoration work. Where materials such as plasterwork, stonework, carved wood and cast iron are used, the mesh captures millable or moldable forms to reproduce and rescale parts to suit restorations. Dry tamped sand and cement could then be compressed into this mold and moisture cured to produce stone pieces. Patterns can be milled for cast iron sand casting. Wood pieces can be remilled. A similar approach can reproduce crumbling terracotta or plaster.
Since 3D printers are capable of printing in metal and transparent materials, restoration of stained glass can use 3D printing as a tool. Ceramic print materials can be used to restore terracottawith the RGB information in the scan file providing a color match for the glaze.
3D printers are falling in price while the 3D print envelope is increasingimproving the printer versatility. LIDAR can soon move from a documentation and CAD enabling tool to a tool that helps build or restore components of the building itself.
David ZipOwner, 3D MobileScan in Edmonton, Alberta, Canada. 3D MobileScan generates 3D surface information using LIDAR for a variety of applications.
Alireza FarrokhiHead, Restoration and Construction Services, Historic Resources Management Branch, Alberta Culture. Ph.D. candidate, Environmental Design, University of Calgary.
Sidebar:
FrostA Tool to Create Surface Files from LIDAR Point Clouds
Frost has roots in the film industry and its need for realistic effects at a 24 frame per second rate. Particle effects such as smoke, blowing sand and environments needed mathematical models that rapidly meshed and produced realistic effects on theater sized screens.
After importing a point file, the main user parameter input is the particle radius that will produce optimal feature definition in the mesh. For the Gas Plant, a scan point radius of .08 units optimized the mesh detail. The generation of the complete mesh takes about 1 minute on an i7 SSD equipped workstation class PC running 64 bit Win7.
Frost’s speed comes from the simplified math in the algorithms coupled with effective use of multiprocessors. The speed allows the time to experiment with different settingslower radius settings yield better mesh definition. The Metaballs algorithm produces sharper detail, while the Zhu-Bridson algorithm produces a smoother surface.
It is possible to export the mesh from 3ds Max as a color OBJ file with the RGB values from the point cloud file used to build a scalable color UV map for the mesh. The original mesh can be decimated to 10% of original size without losing detail using quadratic filters. ZBrush is an excellent post-processing package for color 3D printing workflows.
This file can be uploaded to a 3D print provider and color printed in 3D. The STL format is usable for monochrome 3D printing and milling. The price of Frost is $495 available at Thinkboxsoftware.com.
A 1.054Mb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE