Adds round(), radians2degrees() and degrees2radians() methods to @turf/helpers

[stebogit]

• Adds radians2degrees and degrees2radians to turf-helpers;
• Modified precision of degrees conversion reducing Earth radius to it's average value

[DenisCarriere]

To be further discussed

• Modifying Earth Radius, similar discussion here Update distance measurement factors #635 (comment) (also such change would require a major/minor release). Need a 2nd opinion on this change. (need to open a PR for just that change)
• Remove round() to methods (unnecessary processing?). Edit: At 55M ops/sec I think this is ok 👍

Worth including 👍

• radians2degrees method (without round)
• degrees2radians method (without round)
• round can be included in @turf/helpers. Looks to be a useful method and a modified version has already been used in @turf/truncate - however the multiplier/factor was calculated prior to doing any iterations.

[DenisCarriere]

@stebogit Oops, I thought you did more modifications to the factor. Just realized that you've only changed it from 6373km to 6371km which lines up with what @mourner was discussing in the previous thread.

👍 This PR. Not to sure if this should be deemed a minor release or major release since this will affect a lot of modules.

[stebogit]

@DenisCarriere Why don't we add an optional parameter earthRadius that would default to 6371km, which I agree with @mourner is more correct, or any other value, and the user could decide what value to use.
This way Turf could even land on Mars! 😃

[DenisCarriere]

@mourner's comment does reflect your change, he was mentioning we should use the mean radius which is 6371km, currently TurfJS is using 6373km (dates back over a year ago)

[DenisCarriere]

@stebogit Going to implement radians2degrees, round & degrees2radians, however going to leave the earthRadiusIn/factor changes for another PR (a lot of changes need to happen in dependent modules).

[DenisCarriere]

Merging, build passes on master branch (PR's branch fails on newly updated @turf/buffer)

[mourner]

Why don't we add an optional parameter earthRadius [...], and the user could decide what value to use. This way Turf could even land on Mars! 😃

I don't think there's a need. Distance calculations depend on radius linearly, meaning that for any calculated value using Earth radius you can do distance * mars_radius / earth_radius to adjust the distance value to Mars.

[DenisCarriere]

@mourner Can you confirm/approve the earth radius change (6373km => 6371km)

Should only be implemented in next major release (v5.0)

Ref: #635 (comment) #635 (comment)
CC: @morganherlocker

[mourner]

@DenisCarriere I don't know where 6373 comes from, but the mean radius is 6371: https://en.wikipedia.org/wiki/Earth_radius

[DenisCarriere]

@mourner Agreed, seems like 6373km has been in TurfJS since the beginning, I didn't catch this when I reverted the last earth radius commit since I only I reverted it back to its original state.

https://github.com/Turfjs/turf/blame/c81fc99576a37c38af91527462fd812b6c2bc1d2/packages/turf-helpers/index.js#L273

We will go ahead and change it to 6371km in the next major release.
CC: @stebogit