Fun with parallax

[Joe Durnavich]

I was recently fortunate enough to take a "flightseeing" trip to Denali (Mt. McKinley to you Ohioans),

Way, way cool!

The pilot asked us to estimate the distance to a rock outcropping down the way.

Do you think the clarity of the air made the outcrop appear closer?

[sts60]

It may have helped, but I've been in plenty of clear-air places with long sightlines and/or mountains. It was really due to the unfamiliarity of the landscape. It's just hard to describe adequately.

[JayUtah]

It's more to do with the generic unfamiliarity of landscape. Beyond a few meters, the best distance cue is apparent size. Terrain is generally too abstract to provide apparent size cues. That's actually what fouls us up with Apollo photos. The mountains are rounded. On Earth, rounded terrain is usually a small hill while mountains are craggy and sharp. That's why we mistake those 5,000 foot mountains for 500 foot hills and thus wrongly think they're closer. Of course the lack of air and haze does make a difference, but you can be fooled like that on Earth too.

[sts60]

To elaborate a little, I've hiked on mountains and walked on snowfields and glaciers before. But the unique (to me) combination of the three found there, with no vegetation apparent, made it effectively a "lunar" landscape, minus the "rounded" part that Jay mentioned. Even though I did have the advantage of direct stereo viewing, since I have two eyes in good working order. It would have been no easier if I was just looking at a photograph!

[PhantomWolf]

jayutah said:

It's more to do with the generic unfamiliarity of landscape. Beyond a few meters, the best distance cue is apparent size. Terrain is generally too abstract to provide apparent size cues. That's actually what fouls us up with Apollo photos. The mountains are rounded. On Earth, rounded terrain is usually a small hill while mountains are craggy and sharp. That's why we mistake those 5,000 foot mountains for 500 foot hills and thus wrongly think they're closer. Of course the lack of air and haze does make a difference, but you can be fooled like that on Earth too.

It can happen below water too. We have some springs that are some of the clearest in the world. They are a diving attraction, but it's hard to judge your depth because the 100m deep springs appear only 30m or so.

[sts60]

Here are the pictures from the plane trip to Denali. I just shuffled through the snow in my sneakers to get some different foregrounds. The idea was simply to show a significant change in the foreground with ~no change in the background, so I cropped and resized appropriately.









There's a somewhat trapezoidal area of rock slanted "down and to the right", located just above and to the right of the center of the picture. That is the rock face we were guessing to be a mile or two away, but was actually eight miles.

Larger versions of these images are here, here, here, and here.

[sts60]

Of course, the pictures are obvious fakes - we're on a glacier up in the mountains, but there are people wearing T-shirts and no oxygen... Nor, of course, are there any stars visible.

[LunarOrbit]

That snow looks so good right now...

[Joe Durnavich]

Tell me about it. Our office has been without air-conditioning more often than not this summer, including today. There are no open windows either. (Yet! I'm looking for objects to throw through them.) I don't know why, but 90-degree office heat is unbearable.

[Joe Durnavich]

That is the rock face we were guessing to be a mile or two away, but was actually eight miles.

In the name of science, sts60, what we have to do is fly you back there and let you hike the distance to the rock face and back again a few times so that you develop some perceptual experience with this kind of environment. Then you can tell us if it still looks only a mile or two away.

[sts60]

I'm game. But I won't wear tennis shoes this time. And you have to reserve the cabin for me (famed bush pilot Don Sheldon built one there back around '70 for pilots and hikers; there's about a two-year waiting list). The cabin is on a ridge "over your left shoulder" as you look into the picture.

[Joe Durnavich]

With the heat today, I thought about offering to do it, but on second thought, what really sounds good right about now is a pair of that liquid-cooled underwear the astronauts wear.

[JayUtah]

Even with the LCG the heat has to have someplace to go.

Anyone who wants to show up at my work can spend as long as they want in our final assembly room, affectionately known as Antarctica. 2,700 square feet with 240 tons of air-conditioning. Average temperature, 62 F (unless a big system is running in there).

[craiglamson]

jayutah said:

Even with the LCG the heat has to have someplace to go.

Anyone who wants to show up at my work can spend as long as they want in our final assembly room, affectionately known as Antarctica. 2,700 square feet with 240 tons of air-conditioning. Average temperature, 62 F (unless a big system is running in there).

OH! that sounds wonderful. My studio generally runs air temp +10. Inside a rv with 20,000 watts of tungsten lights is even hotter. I lose a LOT of weight in the summer

[PhantomWolf]

jayutah said:

Even with the LCG the heat has to have someplace to go.

Anyone who wants to show up at my work can spend as long as they want in our final assembly room, affectionately known as Antarctica. 2,700 square feet with 240 tons of air-conditioning. Average temperature, 62 F (unless a big system is running in there).

Can I bring my camping equipment?