turf.lineOffset precision

Hello, I’m using line offset to build parallels to short segments (a few kilometers long) but I found an issue with the precision of the function:

const turf = require('@turf/turf')
const line = turf.lineString([ [4.35,50.845], [4.347,50.85] ])
const parallel = turf.lineOffset(line, 1) // kilometer
const distance0 = turf.distance(line.geometry.coordinates[0], parallel.geometry.coordinates[0])
const distance1 = turf.distance(line.geometry.coordinates[1], parallel.geometry.coordinates[1])
console.log(distance0, distance1)
// output: 0.7468818837096454 0.7468398187109684

This can be reproduced at other places in the world. Any idea on how to improve precision? Thanks.

[PereUbu7]

I made a PR for this: https://github.com/Turfjs/turf/pull/1949 But couldn’t get my env going, so it’s untested.

[devleaks]

To be honnest, I redid the function I needed, it is quite easy: For line (p1, p2), compute the bearing p1->p2. Add or substract 90° to the bearing. Use “destination” function to compute a point with calculated bearing and supplied distance from p1 and from p2. I understand this might not be a “parallel” in spherical geometry, but for short segments (a dozen kilometer long), it is acceptable. I will not work for larger segments. Regards. P.