Editor’s Note: GIS & You is publishing two companion articles describing a project to create a physical 3D model of King County. Each article is written from the perspective of one of the two analysts who worked through the process to make the model a reality. Please see the accompanying article titled “Virtual to physical: translating a 3D landscape to a printed model” for a more complete picture of this complex effort.
In March of 2019, King County Emergency Management submitted a request to KCGIS Center Spatial Services for a tabletop 3D model of the county to be used for community outreach and education on the variety of physical topography throughout King County and its challenges for emergency management.
The request was for an E-size (3×4-foot) model that could be separated into four pieces for portability and have aerial photography printed on top with cities, roads, and water bodies.
A search for local printers who could do the job was made. Many companies can print in one color only and only two vendors could be found who could print the color aerial image on top of the model. One company prints on a ceramic-like material and the other prints on plastic. The ceramic version was more vulnerable to breaking if dropped and had a maximum size of 10 inches per tile. It would take at least 12 tiles (3×4) to make the model. Since the model was going to be carried around and exposed to the public, it was decided to go with the more expensive plastic version, by the company FATHOM, for durability and fewer pieces (four).
It was King County’s responsibility to provide the 3D digital terrain model and aerial photo overlay image to FATHOM. The printer needed an OBJ type file which is a standard 3D software format developed by Wavefront Technologies. Esri’s ArcMap does not support 3D format export directly. So a grayscale 24-bit image of King County’s lidar data was exported from ArcMap and imported into a 3D program to be turned into a terrain, then exported as an OBJ file. At first, the 3D program Carrara was used. It has an easy to use terrain modeler but has an 8-bit limit for export. This resulted in the terrain being sliced into 256 values causing a terracing effect to the topography. Another 3D program called Blender was used to import the grayscale bitmap for plane displacement into a terrain for a smoother model.
The color basemap was produced in ArcMap using 2017 Pictometry aerial photos, 2019 city boundaries, major and minor roads, and waterbodies with labels, all clipped to the same extents as the model and sent to FATHOM.
FATHOM edited the digital model by splitting it into four pieces, honeycombed the underside to save material, weight, and cost, and added tabs so that the pieces would fit together. The model was printed at FATHOM’s Oakland California facility using the 3D printer Stratasys J750 PolyJet. This kind of 3D printer can print in many types of media and color. The size of the four model pieces was maximized to the printer’s limit for a total model size of 975x693x45 mm. The vertical scale of the mountains was exaggerated 2x to emphasize elevation differences between the urban lowlands and the rural uplands.
3 thoughts on “Converting digital terrain data into a 3D printed model of King County”
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