43 lines
1.8 KiB
Markdown
43 lines
1.8 KiB
Markdown
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# WhatFreeWords
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[![](http://www.wtfpl.net/wp-content/uploads/2012/12/wtfpl-badge-4.png")](http://www.wtfpl.net/)
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This is the Dart port of the original [JavaScript implementation](https://github.com/pballett/whatfreewords) that was published as a small test to show how one might reversibly map each ~1m² element of the globe onto a 3-tuple of words.
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## Installation
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In your Flutter/Dart `pubspec.yaml` file include
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```yaml
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dependencies:
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whatfreewords:
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git:
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url: https://github.com/randogoth/whatfreewords.git
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```
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## Usage
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```dart
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import 'package:whatfreewords/whatfreewords.dart';
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// coordinate to wfw
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final List<double> coord = [51.50844113, -0.116708278];
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final words = coordToWords(coord);
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print(words); // demagogue.shuts.troll
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// wfw to coordinate
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final coords = wordsToCoord(words);
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print(coords); // [51.5084, -0.1167]
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```
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Check it out [here](https://pballett.github.io/whatfreewords/).
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To do this we needed three things:
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1. A function which maps metre-accurate (latitude, longitude) pairs into three 5-digit integers below 40k.
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2. An ordered list of 40k words which acts as a bijection between integers and words.
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3. A scrambling function which can be called in the first function to ensure nearby (latitude,longitude) pairs are mapped to very different integers
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Note that all of these functions must be invertible for the mapping to be reversible.
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The scrambling function implemented here is inspired by format preserving encryption: it maps a sequence of 14 digits to another by passing it through a [Feistel network](https://en.wikipedia.org/wiki/Feistel_cipher). There is no need for this encryption to be secure, so the implementation has been simplifed. The point is just to map 14-digits to 14-digits, to exhibit sensitive dependence on the input and to be reversible.
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