56 lines
2.1 KiB
Markdown
56 lines
2.1 KiB
Markdown
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# Map3Terms
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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) of a small but ingenious test to show how one might reversibly map roughly each square meter of the globe onto a 3-tuple of words using a simplified symmetric encryption method called [Feistel cipher](https://en.wikipedia.org/wiki/Feistel_cipher).
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It seems inspired by the existing proprietary geocoding service [What3Words](https://wiki.openstreetmap.org/wiki/What3words) but uses a completely different method and list 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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map3terms:
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git:
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url: https://github.com/randogoth/map3terms.git
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```
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then run
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```
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dart pub update
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```
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## Usage
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```dart
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import 'package:map3terms/map3terms.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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---
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## Original README
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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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