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. Evolving stereoscopy—with tools such as flicker glasses and new measuring capabilities—will be way more immersive and powerful.

Even brightest tablet screens are a challenge for 3D viewing when sun is shining. Fortunately, most days here, that’s not a problem.

Above: Old-fashioned pocket stereoscope over 7-inch tablet, which has room enough to see an entire 3D pair. While tablets are best for classroom use . . .  ●  Below: . . . I’ve recently decided my much smaller phone works fine if rotated into ‘landscape’ position. ‘Spread-zooming’ to maximum separation your eyes can deal with (~70mm ), we may no longer see the entire stereogram, but can pan around to examine any area of interest. Here, we’re viewing the 1926 stereopair for Chas’héeni (Sheep Creek) directly from JuneauNature. Stereo works well in Zoom presentations if your listeners place stereoscopes over their on-line tablets. They can even see the presenter’s cursor, pointing out features on 3D terrain.

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 higher-res 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 phones and 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 phone or 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 during forest and wetland bushwhacks.

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.

Bog and scrub forest on southern Tàan, sea lion (Prince of Wales Island). Yellow line is our GPS track. Dots are photopoints, auto-linked in Robogeo. Studying topography and canopy texture in 3D back at camp, we were better able to delineate patches of upland forest (red tint) from the wetland matrix.

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.

Stereo pair from quadcopter passing over Robin Trib of Eix’gul’héen, warm springs creek (Switzer). Best viewed on tablet or high-res laptop screen with pocket stereoscope. Trampled paths through the waist-high vegetation are mostly from bear traffic; few humans leave the boardwalk here.

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