I wrote this as an appendix to my report with Kathy Hocker on repeat photography. It reviews trends in a…2013 | Richard Carstensen | 6 pages
The land in 3D: resuscitating stereoscopy
It used to be that every forester and field geologist was proficient in stereo-photo interpretation. The digital age has briefly distracted us, but a few cartographers are bringing it back, and the evolving stereoscopy—with tools like flicker glasses and new measuring capabilities—will be way more immersive and powerful.
If you properly size stereo-pairs such as these examples on your computer monitor (about 70 mm across either of those paired images), you can hold a pocket stereoscope to the screen and the landscape will ‘pop up.’ But those lenses typically magnify by 2x, and at that power, on most monitors, you’ll see the pixel-grid, giving a disappointingly grainy view. Tablets, however, (and some of the higher-resolution laptop screens) have smaller pixels that don’t show under 2-power blow-up. Magnified stereo airphoto viewing is beautifully suited to the high resolution and rich color on Android and Apple tablets. In fact, it’s the only use that really justifies their ridiculously high pixel density.
For stereo-viewing, no printed color photos can match the resonance of a backlit aerial on a mini or full-sized tablet. In future posts, I’ll share some of the ABCs of creating and using stereograms. For now, I’ll only note that stereo-interpretation has been a key tool in my recent consulting work, thanks largely to tablets. Although slightly less convenient in the field than my little 3D slide viewers, I frequently stop for a 3D orientation fix on forest and wetland bushwacks.
It’s handy for post-field processing as well. Back in camp or office, I drop the day’s GPS track, waypoints, and autolinked photopoints onto one of the 2 paired images. Then, habitat-mapping is enhanced by an order of magnitude more spatial information than when tracing polygons over a flat, 2D image.
Stereo adds information to all scales of imagery, from ultra-high-elevation NASA flights delivering inch-to-the-mile, down to creek-skimming Beaver flights that show individual alder branches. UAVs (unpersoned aerial vehicles) have the ability to acquire even lower-elevation, high detail stereo, unavailable from traditional aircraft. Below is a pair taken at about 150 feet elevation over uplift parkland, with a Ricoh GR pocket camera, strapped to a quadcopter.