Uber maintains an open source library called H3 which they use in their mobile apps. H3 is based on the concept of dividing the surface of the planet into a grid of hexigons or 'cells'. Each call has a unique identifier and a fixed size and location. This type of grid system is much more powerful than a simple grid of latitude/longitude which produces a set of 'rectangles'. The H3 code library can be used in various ways:
- Given a latitude/longitude point, find the index of the containing H3 cell
- Given an H3 index, find the latitude/longitude cell center
- Given an H3 index, determine the cell boundary in latitude/longitude coordinates
- Find the coordinates of the 6 points for any cell
- Find the distance from a point to the cell edge
Furthermore, H3 defines more than one grid size for the planet. In fact H3 defines 16 distince 'resolutions' ranging from 0.0000009 km^2 up to 4,250,546.8477000 km^2. There is a parent/child relationship between two cells at adjacent resolutions.
Read more about the H3 grid system here: https://h3geo.org
H3kit primarily uses SwiftPM as its build tool, so we recommend using that as well. If you want to depend on H3kit in your own project, it's as simple as adding a dependencies clause to your Package.swift:
dependencies: [
.package(url: "https://github.com/dividenconquer/h3kit-ios.git", from: "1.0.0")
]If your project is set up as an Xcode project and you're using Xcode 11+, you can add H3Kit as a dependency to your
Xcode project by clicking File -> Swift Packages -> Add Package Dependency. In the upcoming dialog, please enter
https://github.com/dividenconquer/h3kit-ios.git and click Next twice.
import H3kit
func testH3() {
let latitude = 40.1234
let longitude = 98.5432
let resolution: Int32 = 14
let point = CLLocationCoordinate2D(latitude: latitude, longitude: longitude)
let index = point.h3CellIndex(resolution: resolution)
let hex = String(index, radix: 16, uppercase: true)
print(hex)
let neighbors = point.h3Neighbors(resolution: resolution, ringLevel: 1)
for item in neighbors {
print(String(item, radix: 16, uppercase: true))
}
}The C librarary has a rich set of APIs documented here: https://h3geo.org/docs/api/indexing You can access the entire API from your Swift based project. Here are some of the main functions:
H3Index geoToH3(const GeoCoord *g, int res);
void h3ToGeo(H3Index h3, GeoCoord *g);
void h3ToGeoBoundary(H3Index h3, GeoBoundary *gp);
void kRing(H3Index origin, int k, H3Index* out);
int maxKringSize(int k);
h3LineExample showing how to take a set of 2D coordinates and generate the set of cells sourrounding that position.
// Determine the set of nearby H3 cells based on location
let latitude = degsToRads( 41.3343 ) // MUST convert to radians
let longitude = degsToRads( 101.1188 )
var location = GeoCoord(lat: latitude, lon: longitude)
let index = geoToH3(&location, 6)
let count = Int(maxKringSize(1))
var neighbors = Array(repeating: H3Index(), count: count)
kRing(index, 1, &neighbors);MIT License
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