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Map Enthusiasts @sopuli.xyz

Flying Squid @lemmy.world

3w ago

Using a human head to demonstrate map projections

67 comments

- Chad projection.
- That's Gall-Peters, isn't it?

Potion seller. I'm going into battle and I need your strongest potions.
- You can't handle my strongest potions traveler
- https://m.youtube.com/watch?v=R_FQU4KzN7A

This has got to be wrong. A human head, projected like a world map, would show both eyes and both ears, except in the case of showing only one half (like when you only show/photograph the Americas).
This appears to take a picture of the side of the head (i.e. that particular projection, showing less than half of the full globe), then distort it as if it were already a different projection.
Edit: worse than that. The globe onto which the half-head-image is superimposed in the top right is larger than the head. Like if you took a photo of the Americas half of the world from space, pasted that onto a larger beach ball, then stretched the result to demonstrate the projections.
- For a better visualization of how a human would look on the mercator projection, look no further than old games' 3D textures, like this one from Half Life: https://www.textures-resource.com/fullview/6384/?source=genre
  
  Oh wow that website is so nostalgic even without the textures!
  
  Taking a second look at that, though - is that really a continuous projection? Or is that storing different parts as different chunks (and maybe projected differently) put together into the one image?
  
  Huh, neat!
- Possibly. I asked (and no one's answered yet, so I still don't know) if it's still a Mercator projection if you vertically bisect a map of the Earth.
  
  It's still a Mercator projection if you take any part of a map projected thusly. (And there's the "modified universal transverse Mercator" that, I think, is that with some grid offset.)
  But, see my edit, this image isn't doing that. It's stretching a "picture of half a face superimposed on a larger half globe," not the half-face as if the head were the globe.
  
  Yes. Why wouldn't it be?
  Projections don't have to be limited to the entire earth. You can subset the area represented and still apply a projection. (Though you do have a decision if you're taking an arc-area to "re-align" your projecting shape so that it best fits your area. But that might be more complicated than you're looking for, other projections best suited for your locale would be a better fit)

Surprisingly informative

The virgin Globular map vs the chad Mercator map

I don't quite get this. The human head, like the globe, is not flat. Shouldn't that be reflected in the projections? When projecting the earth in Mercator, we see the whole earth, not simply a "profile" of earth. I would expect a projection of a head to include the whole surface of the head, not a simple profile. How is this actually factual?
- This isn't representing projections of a human head. This is representing projections of the globe if the globe had a giant human head drawn on it instead of the continents.
  
  But then you have to figure out how to transfer the drawing of the head onto the curved surface, and how you do that is going to determine how the projections look.
- This is a better example
  https://i.imgur.com/4P15yEq.png
  
  ptsd from modding kicks in
  
  That is also a good explanation for how the Shroud of Turin could not possibly be an after-image of a three-dimensional person.
- Same thought, ha.
- It's still a Mercator projection if you take a world map done in that way and cut it in vertically in half, isn't it?

Thats honestly fantastic lol

Which should I use when sending one of my "special" DMs?
- I don't know, and I've also never used a dating app, but I'm swiping whichever direction means "no, I only date people with normal heads."
  
  What about people in robes and wizard hats

OK, now show us the Goode homolosine equal-area projection human head.
- I would, but I have a weak stomach.
  
  So how about the Cahill Butterfly projection, ...

Unlike the human head, the earth actually is nearly spherical. There's got to be some differences in how spherical projections work when the object actually is a sphere, I would think. I know that 2D maps are distorted, but are globes actually this distorted as well? Never knew that, if so.
Edit: After reflecting on it for a minute, I see they're demonstrating forms of 2D map distortion. The way depth is represented is variable. With modern concepts of 3D imagery, we must have solved this distortion problem. If you open up Google Earth's globe, it doesn't have such distortion.
- All 2D projections are distorted, but some are useful in certain contexts (yes, even Mercator, though not for viewing the entire globe at once). Google Earth is still projecting the image of a globe onto a 2D screen, and there are distortions.
  Here's South America straight on in Google Map's globe view:
  And South America from the side:
  If you measure the distances between, say, Manaus and La Paz with your fingers in these pictures, you'll get different answers. That's just how translating a 3D object to a 2D image works; you can't flatten a globe into a piece of paper without breaking something.
  
  Thank you for illustrating for me. I understand what you're saying.
- With modern concepts of 3D imagery, we must have solved this distortion problem.
  ? You're still taking a three dimensional earth and displaying it on a 2d screen or plane. That will always have distortion on some axes. That's not a technological "problem" to be "solved", that's just mathematical reality.
  
  Yes, that's my point, we have computers that can pretty accurately represent depth, not like the old projections we drew on maps. Stretching it out flat (zooming in on google earth) has less distortion than these projections shown here, don't they?

Now do my dick
- =o

List video game musics that would go nicely along with this one in a "scientific diagrams that look like shitposts" video!
- https://youtu.be/nWfRO1yxaXs

This is perfect lmao

That looks pretty accurate for me

Now do Dymaxion
- Is that the orange peel one?
  
  Depends on how you peel an orange

67 comments