July 24--Chattanooga long has touted itself as the Scenic City, but until a few weeks ago, those who visited via the
The detailed satellite imagery used in Google's free mapping software looked fine when viewed from above. But from other angles, the city appeared to be featureless flatland with two-dimensional buildings pasted onto it.
Earlier this summer, however, Google gave Chattanooga a boost into the third dimension courtesy of a new mapping process that automatically generates detailed virtual models of every building, bridge and tree in the city.
When the updated imagery went live earlier this summer, Chattanooga was the first major city in Tennessee to receive a 3D upgrade. In an emailed response, Google couldn't indicate any reason why the Scenic City was at the head of the line.
"Publishing 3D imagery hinges on a variety of factors -- everything from data complexity to computing and resource availability," wrote Susan Cadrecha, Google's communications senior associate of maps, in an emailed response.
"There was no reason specifically for Chattanooga to go ahead of other [Tennessee] cities, but we are looking forward to expanding 3D coverage in the future."
The models created using Google's new approach don't always bear up under close scrutiny. Some buildings appear distorted, causing them to appear to have been constructed from melting taffy. Because of how Google's algorithm interprets them, streets with a thick canopy of trees -- as is in the Fortwood Historic District downtown -- can sometimes mistakenly be modeled as green tunnels.
What the technique lacks in finesse, however, it makes up for in comprehensiveness. Every building in the city, from AT&T Field to Hamilton Place Mall, has been virtually replicated.
Prior to Google's new technique, generating virtual models for Google Earth was a laborious process. Users first had to take photographs of each side of a building and apply these images as a texture "skin" to a model created using 3D modeling software. The final model then had to be submitted to Google to be reviewed before being placed on the virtual globe. From start to finish, the process could take several months.
In a June 2012 post to Google's official blog announcing the new mapping technique, Google Map vice president of engineering Brian McClendon explained how the company had streamlined its modeling process by using a fleet of camera-equipped planes.
By making multiple passovers of a city from four cardinal directions and combining those building profiles with top-down satellite imagery using an algorithm, Google is able to generate models much more quickly than any manual process, McClendon explained in a 2012 interview with CNET.
"The ability to generate this imagery automatically means that, just by using computer vision, we can generate large swaths [of models], much larger than has been available," McClendon said. "With this methodology, we can cover the entire cityscape ... with just algorithm."
Google's first batch of 3D-mapped cities went live in June 2012, enabling users to virtually explore close-to-exact digital replicas of major cities such as San Francisco, Boston, Los Angeles, San Antonio and Rome.
Over the last two years, Google has extended 3D coverage to many mid-size cities, including Louisville, Ky., Greensboro, N.C., and Montgomery, Ala. Chattanooga's 3D upgrade went live in June and extends beyond downtown to outlying areas, such as Signal Mountain and Harrison to the north and North Georgia towns such as Ringgold and Flintstone.
Weeks after Chattanooga's map data was updated, Nashville and Memphis also received the 3D treatment. Knoxville, however, remains mostly flat, save for a handful of models created and uploaded to Google by users.