Terrain Visualization with 3DAR

The Spot Metrix team has been experimenting using 3DAR for terrain visualization over the past months. This started as an effort to increase the accuracy of augmentations and, while we came up with some cool results, this problem presented some challenges.

The primary issues were related hardware limitations. Our devices’ GPS receivers provide unimpressive locational accuracy, which is crucial, as the accuracy of any augmentation drawn in 3DAR is a function of the accuracy of the device’s assumed location. The accuracy of the device’s longitude and latitude can be acceptable for some forms of augmentation, but GPS is much, much worse at providing an accurate altitude value due to the geometry of the satellite network. In the image below, you see that GPS satellites can provide signal from one “side” of a  given location on earth, that is, the “space side”. Without a signal from the “earth side”, the vertical accuracy cannot compare to the horizontal accuracy. The high-accuracy GPS receivers used for surveying can achieve impressive vertical accuracy (within 5 cm), but these receivers read the phase of the GPS signal (in addition to the code signal commercial GPS devices read) and rely on an extensive network of terrestrial differential correction stations.

source: Dept. of Mathematics, Texas A&M

Knowing that we couldn’t rely on GPS for an accurate altitude reading, we used Google’s Elevation API, both to find the users approximate elevation and to collect regularly-spaced points to build our elevation grid. We added a meter, or two, to the users elevation to determine presumed device altitude. While more accurate, this approach still relied on a potentially inaccurate horizontal location that could result in a substantial deviation in device altitude in areas of sharply varying terrain. For instance, what if you’re 20 stories up looking out a window? Clearly, we’re going to need to find a more reliable and accurate positioning system before terrain-aware augmentation can become ubiquitous.

While these issues limited our ability to achieve true terrain-aware augmented reality, they didn’t stop us from doing some fun experiments with immersive 3D mapping. Check out this video, courtesy of Max Ogden:

We’ve been working with terrain visualization on and off for a while and we’re still excited about potential applications. If you’re interested this technology, get in touch!