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hyperbolic-canvas's Introduction

Hyperbolic Canvas

A Javascript implementation of the Poincaré disk model of the hyperbolic plane, on an HTML canvas.

Usage examples can be found on the project site.

Installation

Via NPM

npm install --save hyperbolic-canvas

In-Browser

<script type="application/javascript" src="dist/hyperbolic_canvas.js"></script>

Usage

Pass a unique selector of a div element, to the function HyperbolicCanvas.create. Nonzero width and height styling must be specified. Absolute px values in a 1:1 ratio are recommended:

<div id="hyperbolic-canvas" style="width: 600px; height: 600px;"></div>
let canvas = HyperbolicCanvas.create('#hyperbolic-canvas');

API

See API.md for a list of functions and their descriptions.

Scope

This library prioritizes the visualization of hyperbolic geometry over precise mathematical calculation. Due to the less-than-infinite precision of floating-point numbers, and because certain trigonometric functions are ill-conditioned, these goals are often at odds.

Accuracy Thresholds

The arbitrary constants HyperbolicCanvas.INFINITY and HyperbolicCanvas.ZERO have been defined for use in internal comparisons in place of Infinity and 0, respectively. Their values may be overridden, but increased accuracy will tend to lead to more unpredictable behavior.

Jasmine Specs

This library uses Jasmine specs to validate the code and prevent regressions.

The specs have been written to use random input values. While this approach is unconventional, it provides more confidence than would an attempt to test an effectively infinite number of edge cases. Some specs do occasionally fail; the frequency at which this occurs is determined by the accuracy of the constants HyperbolicCanvas.INFINITY and HyperbolicCanvas.ZERO.

The Jasmine library itself has been modified to run each spec multiple times, and a random number seed is used so that errors may be reproduced. The seed and the spec run count can be set in the options menu on the SpecRunner page.

Browser Support

Certain browsers do not provide support for the hyperbolic trigonometric functions. Polyfills are available.

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hyperbolic-canvas's Issues

Line object is too vague

The Line object currently represents lines, line segments, and rays, in both the Euclidean and hyperbolic sense. This is potentially confusing, and the Line object should be split into multiple objects.

Range Error: Maximum Call Stack Size Exceeded in Point.js [not a bug]

When I was working on a hyperbolic geometry idea the Point.js script threw an error with a huge call stack, consisting of these three over and over:

isIdealPoint.js:256
getHyperbolicRadiusPoint.js:63
getEuclideanRadiusPoint.js:42

Apparently isIdealPoint calls getHyperbolicRadiusPoint which calls getEuclideanRadiusPoint which calls isIdealPoint... perhaps, change isIdealPoint to not use the other two functions?

NOTE: I'm not sure if this bug even exists or if my version of the library is outdated.

[Question] How to deal with polar coordinates?

Hello, and thanks for the nice software! It fits best for my school project, so I would like to learn how to use this software, but I'm having troubles understanding it.

Given Poincaree disk, represented as a circle in the Cartesian coordinate system, centered at the origin (0, 0) and having radius 1, I have some questions:

Question 1

Given a point in hyperbolic plane defined using hyperbolic polar coordinates (r, φ) that projects into the point (x, y) (Euclidean non-polar coordinates) on the Poincaree disk, how to express x and y respectively using r and φ? What formula would it be?

Question 2

Given two points in hyperbolic plane P1 and P2 defined using hyperbolic polar coordinates (r1, φ1) and (r2, φ2) respectively. Given polar hyperbolic point P3 (r3, φ3) as the linear interpolation between P1 and P2 parametrized with some variable k (between 0 (gives P1) and 1 (gives P2)). How to express r3 and φ3 using r1, φ1, r2, φ2, k?

Question 3

Given hyperbolic line L1 defined by polar hyperbolic points (1, 0) and (1, π). Given hyperbolic line L2 that is parallel to the L1 (in hyperbolic plane) and that, when projected to the Poincaree disk, has vertical symmetry. Given hyperbolic polar point Q on L2 that is closest to the origin and hyperbolic distance from Q to the origin is n, and Q projects above the origin on the Poincaree disk. The set of all hyperbolic polar points on line L2 is defined as P(k) where parameter k is a real number in range (-∞, +∞), such that for k < 0 points project to the left side of the Poincaree disk and for k > 0 points project to the right side of the Poincaree disk, while P(0) is Q. Question: how to express P(k) using n and k?


Note: I tried to make questions mathematically formal in order to avoid confusion or spoken language imprecision. I was also reading math papers and wikipedia page about hyperbolic geometry, but still can't find answers to these questions.

Regarding question 1: I read source code and if I understand correctly, x = tanh(r / 2) * cos(φ) and y = tanh(r / 2) * sin(φ), is that correct? If yes, where did the formula come from?

Regarding question 2, I tried to define two hyperbolic points and draw a line between them by iterating k from 0 to 1 and drawing small straight line segments between two consecutive interpolated points. However, no matter what I try, the arc curves to the opposite direction and is mislaced on the Poincaree disk. Same happens regarding question 3: the line curves downwards instead of upwards.

Precise formulas for all 3 questions would be preferred over spoken language explanation, since I am trying to finish my project and I can later understand how it works. Thank you in advance for your time.

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