Tissot's indicatrix | Hacker News Reader

Tissot's indicatrix

observablehq.com

67 pointszeroday2816 comments

For a bit of context: https://en.wikipedia.org/wiki/Tissot%27s_indicatrix

This is an essential tool to teach, not only map projections, but the more general concept of Riemannian metrics!

See also the Dupin indicatrix, whose wikipedia article unfortunately lacks good figures: https://en.wikipedia.org/wiki/Dupin_indicatrix (it makes a funny appeal to "just imagine them"...)

Thank you. Without this, I was trying to understand how the code snippets were related to the watch brand Tissot.

I’d heard of a Dupin cyclide but not this, thanks.

Somewhat related (if you’re one of today’s lucky 10,000):

https://xkcd.com/977/

or further afield, Spilhaus: https://www.esri.com/arcgis-blog/wp-content/uploads/2019/09/...

> Spilhaus

Which itself is a combination of Hammer & Spielmann, centered on Antarctica.

https://www.geographyrealm.com/the-spilhaus-endless-ocean-ma...

I was looking for Dymaxion in the dropdown list and it's not there :(

It doesn't have Euler Spiral[1] either, but maybe that's expecting too much.

[1] http://andersk.mit.edu/euler-spiral-projection/

> Euler Spiral

AKA the "apple peel" projection.

Which language is used in the code boxes here? is this a JavaScript extension?

The answer is probably in here https://observablehq.com/documentation/cells/observable-java... but i still don't see why you can do `x = { let y = 5; return y }`

I think that's a combination of two features, named cells[1] and blocks[2].

[1] https://observablehq.com/documentation/cells/javascript#nami...

[2] https://observablehq.com/documentation/cells/javascript#expr...

> Named cells look like, and function almost like, assignment expressions in vanilla JavaScript

> But sometimes you want statements, such as for loops. For that you'll need curly braces, and a return statement to give the cell a value. Think of a cell as a function, except the function has no arguments

So `x = { let y = 5; return y }` declares named cell x with value from the return value of that function-like code block. So basically that should be same as `x = 5`, which also is named cell declaration and not JS variable assignment.

And here I was thinking this was a new watch from Tissot :-)

Same. What I found was far more interesting and educating.

Ha, my first thought too. Some new kind of movement to follow the Powermatic 80, perhaps?

But like someone else said, a very interesting read.

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