Maptiles represent latitude of 0 as an inaccurate float

[davidjb]

When using maptile to compute tile bounds, if you try and compute a latitude for a tile that involves the equator, you'll end up with an inaccurate float as a result - instead of 0, you get -0.00000000000000038584785111248965 aka -3.8584785111248965e-16. Calculations that depends on this value then become inaccurate (e.g. 0 > -0.00000000000000038584785111248965 gives true) as do equality comparisons and so on.

Calculations involving the longitude don't appear affected and represent 0 accurately, and the resulting floating point for 0 always appears consistently at least. See below:

package main

import (
	"fmt"

	"github.com/paulmach/orb"
	"github.com/paulmach/orb/maptile"
)

func main() {
	fmt.Println("Tile below equator")
	for i := 1; i < 6; i++ {
		tile := maptile.At(orb.Point{0, 0}, maptile.Zoom(i))
		fmt.Print("Tile ", tile, "\n")
		fmt.Print("\t", tile.Bound(), "\n")
	}

	fmt.Println("\nTile above equator")
	for i := 1; i < 6; i++ {
		tile := maptile.At(orb.Point{0, 0}, maptile.Zoom(i))
		northTile := maptile.New(tile.X, tile.Y-1, tile.Z)
		fmt.Print("Tile ", northTile, "\n")
		fmt.Print("\t", northTile.Bound(), "\n")
	}
}

Tile below equator
Tile {1 1 1}
        {[0 -85.05112877980659] [180 -3.8584785111248965e-16]}
Tile {2 2 2}
        {[0 -66.51326044311186] [90 -3.8584785111248965e-16]}
Tile {4 4 3}
        {[0 -40.97989806962013] [45 -3.8584785111248965e-16]}
Tile {8 8 4}
        {[0 -21.943045533438166] [22.5 -3.8584785111248965e-16]}
Tile {16 16 5}
        {[0 -11.178401873711772] [11.25 -3.8584785111248965e-16]}

Tile above equator
Tile {1 0 1}
        {[0 -3.8584785111248965e-16] [180 85.0511287798066]}
Tile {2 1 2}
        {[0 -3.8584785111248965e-16] [90 66.51326044311185]}
Tile {4 3 3}
        {[0 -3.8584785111248965e-16] [45 40.97989806962013]}
Tile {8 7 4}
        {[0 -3.8584785111248965e-16] [22.5 21.94304553343818]}
Tile {16 15 5}
        {[0 -3.8584785111248965e-16] [11.25 11.178401873711785]}

Tested with orb v0.11.1 and Go 1.23.3.