Thursday, October 14, 2010

Making a flat earth rugged

I'm trying to figure out how long this feature has been a part of Google Earth: when you pan a mountainous scene back and forth, you can see it in three dimensions. I'm pretty sure it wasn't always there, but I've been mostly working in the relatively flat Midwest and didn't notice it until now.

You can see it for yourself by zooming in on any mountainous area, or you can download this file and open it directly in Google Earth to find the location seen here:

What you're looking at is Dome Mountain, a prominent peak at the exit to Yankee Jim Canyon, north of Yellowstone National Park. If you use the right and left arrow keys to pan back and forth, you'll suddenly start seeing the landscape in three dimensions. As soon as you stop, it's flat again.

To do this, Google Earth has to continuously distort the image as you pan. The parts of the image that represent the highest elevation are stretched farther toward the edges of the screen, while the lower elevations stay relatively still. As you'll immediately recognize, this is how you experience the real world: when you move, objects that are close to you seem to change position much more than do those farther away.

I underestimated the amount of distortion, until I compared snapshots of the mountain at the extreme sides of the screen. Here I've placed identical circles at the same point in each one, to make for easier comparison. When the mountain is moved to the left (as if you were viewing slightly from the east), see how much more area the east side of the slope seems to take up. In the image to the right (corresponding to a vantage point slightly more to the west) it's the western side that seems very wide and the eastern slope that is narrowed. Notice the treeless, gullied area on the western slope, which is rendered perhaps twice as wide in the right hand shot as it is on the left.

Keep in mind that Google doesn't have multiple views available. It's all the same flat, 2-dimensional image that is being manipulated in just the right manner to mimic what you'd see if it really were 3-D. Through long experience with the real world, your visual system has learned that close things shift position more noticeably than distant things do, so it can be tricked into thinking you're seeing depth, even when you aren't. Google falsifies the image so that your brain falsely interprets what's really in front of your eyes - all to give you a truer impression of what you'd see if you really were floating above the mountain. Cute trick.

1 comment:

Heather said...

SO COOL. I frickin' love maps. Thanks for finding such interesting things to blog about!