Modeling the BNR Bridge


As part of our continuing contributions to the Google Earth 3D Building menagerie, we just completed a complex virtual model of the Burlington Northern Railroad Bridge here in Portland. Of the 11 spans we use in Bridge City, only the BNR is train-exclusive and closed-off to the public. This means virtually no Google Streetview or other handy orthographic photo reference we might normally use at Fat Pencil.

Here's a view of the BNR Bridge as seen in Google Earth, before we got started.


Of course, this poses a healthy challenge to even the most resourceful and intrepid 3d modeler.

Fortunately, a quick internet search and some links from Google Earth’s Photos layer provided a few images taken from riverbanks and boats. Photoshop’s perspective crop adjusted the images to make suitable backdrops. Instead of merely tracing the images, we used the images to dissect the bridge’s construction, building individual components in Sketchup to piece together. This ensured symmetry, and easy corrections as the model quickly grew in complexity. So, much like the real bridge was constructed 104 years ago, the virtual one is built girder by girder, span by span.

A built structure like this bridge cannot be modeled to the last nut and bolt, because Google Earth won’t accept such an enormous file. The challenge is to strike the right balance between simplicity and realism. In this case, the bridge was successfully trimmed to only 66 components and 21 unique textures. Google Earth only accepts photo-textured models, so one field trip was required to zoom in and snap our own high-res photos of certain elements not visible in other shots. But, any excuse to escape the computer monitor and snag some rare Northwest sunshine is a welcome one.

The BNR Bridge is now live in Google Earth, check it out!

Jeff Harris was an intern at Fat Pencil Studio in 2012.