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
Create a Podfile with the following specification:
pod 'H3', :git => 'git@github.com:ehmjaysee/h3-ios.git'import H3
func testH3() {
let latitude = 40.1234
let longitude = 98.5432
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: 6, 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);