B Can Height, Shadow Length, and a Photo Reveal a Person's Location?

[kent davidge]

I saw the following question in Yahoo Answers,

How do you know where in our planet is a person located, knowing her height, length of her shadow and having a photograph of her on the unkown location, knowing day-month-year and time the photo was taken?

Is it even possible to know this?

 

[russ_watters]

If you have the time in UTC, sure.

 

[DrClaude]

If you have the time in UTC, sure.

But with what error bars?

If you have no orientation information (which way is North?), then there is quite a wide band of longitude+latitude solutions, mirrored on each hemisphere.

 

[russ_watters]

But with what error bars?

Accurate enough to navigate a ship in the 19th century...

If you have no orientation information (which way is North?), then there is quite a wide band of longitude+latitude solutions, mirrored on each hemisphere.

Good point; you would have to know the hemisphere, which maybe you could see from context in the photo.

 

[DrClaude]

Accurate enough to navigate a ship in the 19th century...

Not without a compass

My point is that at any given time, the same stick length will give the same shadow length at many points on the globe. If you have no information on the orientation of the shadow, there is not much you can say.

 

[russ_watters]

Not without a compass

Oh, you don't just mean the hemisphere. Yes, I see you're right; to get the longitude from the azimuth of the sun, you need the actual angle from north.

and...now that I think about it, without longitude (and with it local time) first, the altitude doesn't tell you latitude either.

 

[jbriggs444]

The azimuth just positions you somewhere on a circle that is centered on a point where the sun is directly overhead. A compass heading could position you on that circle.

Edit: if the ground is not level, your navigation could be way off.

 

[sophiecentaur]

maybe you could see from context in the photo.

The one with the penguins in, perhaps.