Table of Contents

Grid traversal functions

Grid traversal allows finding cells in the vicinity of an origin cell, and determining how to traverse the grid from one cell to another.

kRing

void kRing(H3Index origin, int k, H3Index* out);

k-rings produces indices within k distance of the origin index.

k-ring 0 is defined as the origin index, k-ring 1 is defined as k-ring 0 and all neighboring indices, and so on.

Output is placed in the provided array in no particular order. Elements of the output array may be left zero, as can happen when crossing a pentagon.

maxKringSize

int maxKringSize(int k);

Maximum number of indices that result from the kRing algorithm with the given k.

kRingDistances

void kRingDistances(H3Index origin, int k, H3Index* out, int* distances);

k-rings produces indices within k distance of the origin index.

k-ring 0 is defined as the origin index, k-ring 1 is defined as k-ring 0 and all neighboring indices, and so on.

Output is placed in the provided array in no particular order. Elements of the output array may be left zero, as can happen when crossing a pentagon.

hexRange

int hexRange(H3Index origin, int k, H3Index* out);

hexRange produces indexes within k distance of the origin index. Output behavior is undefined when one of the indexes returned by this function is a pentagon or is in the pentagon distortion area.

k-ring 0 is defined as the origin index, k-ring 1 is defined as k-ring 0 and all neighboring indexes, and so on.

Output is placed in the provided array in order of increasing distance from the origin.

Returns 0 if no pentagonal distortion is encountered.

hexRangeDistances

int hexRangeDistances(H3Index origin, int k, H3Index* out, int* distances);

hexRange produces indexes within k distance of the origin index. Output behavior is undefined when one of the indexes returned by this function is a pentagon or is in the pentagon distortion area.

k-ring 0 is defined as the origin index, k-ring 1 is defined as k-ring 0 and all neighboring indexes, and so on.

Output is placed in the provided array in order of increasing distance from the origin. The distances in hexagons is placed in the distances array at the same offset.

Returns 0 if no pentagonal distortion is encountered.

hexRanges

int hexRanges(H3Index* h3Set, int length, int k, H3Index* out);

hexRanges takes an array of input hex IDs and a max k-ring and returns an array of hexagon IDs sorted first by the original hex IDs and then by the k-ring (0 to max), with no guaranteed sorting within each k-ring group.

Returns 0 if no pentagonal distortion was encountered. Otherwise, output is undefined

hexRing

int hexRing(H3Index origin, int k, H3Index* out);

Produces the hollow hexagonal ring centered at origin with sides of length k.

Returns 0 if no pentagonal distortion was encountered.

h3Line

int h3Line(H3Index start, H3Index end, H3Index* out);

Given two H3 indexes, return the line of indexes between them (inclusive).

This function may fail to find the line between two indexes, for example if they are very far apart. It may also fail when finding distances for indexes on opposite sides of a pentagon.

Notes:

  • The specific output of this function should not be considered stable across library versions. The only guarantees the library provides are that the line length will be h3Distance(start, end) + 1 and that every index in the line will be a neighbor of the preceding index.
  • Lines are drawn in grid space, and may not correspond exactly to either Cartesian lines or great arcs.

h3LineSize

int h3LineSize(H3Index start, H3Index end);

Number of indexes in a line from the start index to the end index, to be used for allocating memory. Returns a negative number if the line cannot be computed.

h3Distance

int h3Distance(H3Index origin, H3Index h3);

Returns the distance in grid cells between the two indexes.

Returns a negative number if finding the distance failed. Finding the distance can fail because the two indexes are not comparable (different resolutions), too far apart, or are separated by pentagonal distortion. This is the same set of limitations as the local IJ coordinate space functions.

experimentalH3ToLocalIj

int experimentalH3ToLocalIj(H3Index origin, H3Index h3, CoordIJ *out);

Produces local IJ coordinates for an H3 index anchored by an origin.

This function is experimental, and its output is not guaranteed to be compatible across different versions of H3.

experimentalLocalIjToH3

int experimentalLocalIjToH3(H3Index origin, const CoordIJ *ij, H3Index *out);

Produces an H3 index from local IJ coordinates anchored by an origin.

This function is experimental, and its output is not guaranteed to be compatible across different versions of H3.