https://github.com/developmentseed/dirty-reprojectors

Make quick and dirty projections to use in your web maps instead of Web Mercator
https://github.com/developmentseed/dirty-reprojectors

Last synced: 3 months ago
JSON representation

Make quick and dirty projections to use in your web maps instead of Web Mercator

• Host: GitHub
• URL: https://github.com/developmentseed/dirty-reprojectors
• Owner: developmentseed
• License: mit
• Created: 2016-11-10T16:17:16.000Z (about 8 years ago)
• Default Branch: master
• Last Pushed: 2022-12-03T04:24:45.000Z (about 2 years ago)
• Last Synced: 2024-10-01T17:18:37.929Z (4 months ago)
• Language: JavaScript
• Homepage: https://www.developmentseed.org/dirty-reprojectors-app/
• Size: 1.11 MB
• Stars: 120
• Watchers: 46
• Forks: 10
• Open Issues: 22
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

Awesome Lists containing this project

• awesome-starred - developmentseed/dirty-reprojectors - Make quick and dirty projections to use in your web maps instead of Web Mercator (others)

README

        
# Dirty Reprojectors

Quick and dirty re-projections to trick your web maps out of web mercator.

## Install

    npm install -g dirty-reprojectors

## Usage

### CLI

    cat input.geojson | dirty-reproject --forward PROJECTION [--reverse PROJECTION=mercator] > output.geojson

Example: to reproject some geojson so that web mapping libraries will render it

looking like 'albersUsa':

    cat input.geojson | dirty-reproject --forward albersUsa > output.geojson

For a list of supported projections, `dirty-reproject --list`

### API

#### reproject

Reprojects the given geometry coordinate array _in place_, with

unprojectable points or degenerate geometries removed. If both

`options.forward` and `options.reverse` are supplied, then `forward` is

performed first.

**Parameters**

-   `options` **[Object](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)** 

    -   `options.forward` **([Function](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/function) \| [string](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String))?** The forward projection to use.

    -   `options.reverse` **([Function](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/function) \| [string](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String))?** The reverse projection to use.

    -   `options.projections` **[Object](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)?** A map of named projections to use.  If provided, then string values of `options.forward` or `options.reverse` will be used as keys to look up the projection function in `options.projections`.  For an extensive list provided by d3-geo-projection, use `require('dirty-reprojectors/projections')`.

-   `coordinates` **[Array](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array)** 

## How it works

Take, for example:

    cat input.geojson | dirty-reproject --forward albersUsa > output.geojson

What this actually does is:

1. Project `input.geojson` from WGS 84 (longitude/latitude) into `albersUsa`, with the target coordinates scaled to match the dimensions of Web Mercator.

2. Reverse-project the result back to WGS84 _as if_ it had been projected with Web Mercator.  So now, when your favorite web mapping library tries to project it into mercator, the geometries end up looking like they were projected using Albers.

The main catch is that if you actually look at the longitude/latitude

coordinates in `output.geojson`, they are totally wrong.  (There are other,

subtler catches, too, having to do with Web Mercator's limited latitude range,

varying loss of precision, and probably many other nuances I am not aware of.)

## Credits

 - Inspired by [this trick](https://www.mapbox.com/blog/mapping-arctic-ice-polar-projection/)

 - All the heavy lifting here is thanks to Mike Bostock's excellent [d3-geo](https://github.com/d3/d3-geo) and [de-geo-projection](https://github.com/d3/d3-geo-projection)