New module @turf/projection

[stebogit]

This is a first draft of the module(s) to convert any GeoJSON from WGS84 to Mercator and vice versa, where the conversion functions are taken from sphericalmercator.
Example:

var pt = turf.point([4, 7.5])
var mercator = turf.toMercator(pt);
var wgs84 = turf.toWgs84(mercator);

Do we actually want two separate modules for the conversions or a single one with a parameter?
We might have something like:

var pt = turf.point([4, 7.5])
var mercator = turf.convert(pt, 'wgs84', 'mercator');
var wgs84 = turf.convert(pt, 'mercator', 'wgs84');

I decided to use proj4 as a reference to create the test cases, is that ok?

Ref: #141, #925

[DenisCarriere]

👍 Nice! Looking forward to play with this module 😄

I'm good for using toWgs84 and toMercator, these coordinate conversions should only be used for WGS84 => Mercator => WGS84, anything else more should be handle with custom scripts and not be built-in for TurfJS. The last thing we want is handling projection issues.

I decided to use proj4 as a reference to create the test cases, is that ok?

Proj4 is perfect! I would've used the same.

[DenisCarriere]

Significant recommendation, I would group these methods (toWgs84 & toMercator) in a single module (ex: @turf/projection) and have this module export those two or more methods.

Or we use your 2nd approach, except change convert to projection.

var projection = require('@turf/projection');
var pt = turf.point([4, 7.5])
var mercator = turf.projection(pt, 'wgs84', 'mercator');
var wgs84 = turf.projection(pt, 'mercator', 'wgs84');

[stebogit]

I would group these methods (toWgs84 & toMercator) in a single module (ex: @turf/projection) and have this module export those two or more methods.

This is what I really wanted to do, but I couldn't figure out how to do it, cause I didn't think about that!! 🎉
Excellent, will do! 😃 👍

[DenisCarriere]

Awesome! 👍 Just need to look at @turf/helpers or @turf/meta for multi-function modules.

[stebogit]

@DenisCarriere I am not sure how to handle the 180th meridian issue here: proj4 returns values quite different than sphericalmercator, thus the test fails.
What should be the output for the test case?
Is there anything like geojson.io for Mercator coordinates?

[DenisCarriere]

🎉 @stebogit module published @turf/projection