MERCATOR_A constant unused

[lights0123]

in src/utils/constants.js, MERCATOR_A is defined as a file-local constant:

threebox/src/utils/constants.js

Line 2 in 36d9de7

const MERCATOR_A = 6378137.0; // 900913 projection property

However, when exported, the very similar—but not quite the same—EARTH_RADIUS constant is used instead:

threebox/src/utils/constants.js

Line 10 in 36d9de7

MERCATOR_A: EARTH_RADIUS, // 900913 projection property

That makes the earlier defined MERCATOR_A constant unused. Is this a copy/paste error, or is this truly the way it should be?

[jscastro76]

Hi @lights0123
That's a great question, the fact is that the most precise value is const MERCATOR_A = 6378137.0; // 900913 projection property, is the one that I would use, but is not the one used by Mapbox which includes hardcoded the following:

/*
* Approximate radius of the earth in meters.
* Uses the WGS-84 approximation. The radius at the equator is ~6378137 and at the poles is ~6356752. https://en.wikipedia.org/wiki/World_Geodetic_System#WGS84
* 6371008.8 is one published "average radius" see https://en.wikipedia.org/wiki/Earth_radius#Mean_radius, or ftp://athena.fsv.cvut.cz/ZFG/grs80-Moritz.pdf p.4
*/
export const earthRadius = 6371008.8;

So, to be accurate with Mapbox calculations I decided to modify it to the value they use.

Are you finding any issue in your calculations?

[lights0123]

Nope. However, I'm wondering if the unused constant should be removed and a comment added explaining the use of EARTH_RADIUS.

[jscastro76]

@lights0123 updated the comment, but I decided not to remove the local variable