Geospatial Data Preparation for 3D Printed Geographies

September 19th, 2015 by Claus Rinner

I am collaborating with my colleague Dr. Claire Oswald on a RECODE-funded social innovation project aimed at using “A 3D elevation model of Toronto watersheds to promote citizen science in urban hydrology and water resources”. Our tweets of the first prototypes printed at the Toronto Public Library have garnered quite a bit of interest – here’s how we did it!

claire-dem-tweet_Aug21claus-popdens-tweet_Aug22

The process from geography to 3D print model includes four steps:

  1. collect geospatial data
  2. process and map the data within a geographic information system (GIS)
  3. convert the map to a 3D print format
  4. verify the resulting model in the 3D printer software

So far, we made two test prints of very different data. One is a digital elevation model (DEM) of the Don River watershed, the other represents population density by Toronto Census tracts. A DEM for Southern Ontario created by the Geological Survey of Canada was downloaded from Natural Resources Canada’s GeoGratis open data site at http://geogratis.gc.ca/. It came in a spatial resolution of 30m x 30m grid cells and a vertical accuracy of 3m.

The Don River watershed boundary from the Ontario Ministry of Natural Resources was obtained via the Ontario Council of University Libraries’ geospatial portal, as shown in the following screenshot.

Download of watershed boundary file

The population density data and Census tract boundaries from Statistics Canada were obtained via Ryerson University’s Geospatial Map and Data Centre at http://library.ryerson.ca/gmdc/ (limited to research and teaching purposes).

The Don River watershed DEM print was prepared in the ArcGIS software by clipping the DEM to the Don River watershed boundary selected from the quaternary watershed boundaries. The Don River DEM was visualized in several ways, including the “flat” greyscale map with shades stretched between actual minimum and maximum values, which is needed for conversion to 3D print format, as well as the more illustrative “hillshade” technique with semi-transparent land-use overlay (not further used in our 3D project).

DEM of Don River watershedHillshade of Don River valley at Thorncliffe Park

The population density print was prepared in the free, open-source QGIS software. A choropleth map with a greyscale symbology was created, so that the lighter shades represented the larger population density values (yes, this is against cartographic design principles but needed here). A quantile classification with seven manually rounded class breaks was used, and the first class reserved for zero population density values (Census tracts without residential population).

qgis-3D-popdens-project

In QGIS’ print composer, the map was completed with a black background, a legend, and a data source statement. The additional elements were kept in dark grey so that they would be only slightly raised over the black/lowest areas in the 3D print.

qgis-3D-popdens-composer

The key step of converting the greyscale maps from the GIS projects to 3D print-compliant STL file format was performed using a script called “heightmap2stl.jar” created by Markus Fussenegger. The script was downloaded from http://www.thingiverse.com/thing:15276/#files, and used with the help of instructions written by James Dittrich of the University of Oregon, posted at http://adv-geo-research.blogspot.ca/2013/10/converting-dems-to-stl-files-for-3d.html. Here is a sample run with zero base height and a value of 100 for the vertical extent.

Command for PNG to STL conversion

The final step of pre-print processing involves loading the STL file into the 3D printer’s proprietary software to prepare the print file and check parameters such as validity of the structure, print resolution, fill options for hollow parts, and overall print duration. At the Toronto Public Library, 3D print sessions are limited to two hours. The following screenshot shows the Don River DEM in the MakerBot Replicator 2 software, corresponding to the printer used in the Library. Note that the model shown was too large to be printed in two hours and had to be reduced below the maximum printer dimensions.

Don River watershed model in 3D printing software

The following photo by Claire Oswald shows how the MakerBot Replicator 2 in the Toronto Reference Library’s digital innovation hub prints layer upon layer of the PLA plastic filament for the DEM surface and the standard hexagonal fill of cavities.

DEM in printing process - photo by C. Oswald

The final products of our initial 3D print experiments have dimensions of approximately 10-20cm. They have made the rounds among curious-to-enthusiastic students and colleagues. We are in the process of improving model quality, developing additional models, and planning for their use in environmental education and public outreach.

The printed Don River watershed model

3D-printed Toronto population density map

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