Functions for Working with H3 Indexes

H3 is a geographical indexing system where Earth’s surface divided into a grid of even hexagonal cells. This system is hierarchical, i. e. each hexagon on the top level ("parent") can be splitted into seven even but smaller ones ("children"), and so on.

The level of the hierarchy is called resolution and can receive a value from 0 till 15, where 0 is the base level with the largest and coarsest cells.

A latitude and longitude pair can be transformed to a 64-bit H3 index, identifying a grid cell.

The H3 index is used primarily for bucketing locations and other geospatial manipulations.

The full description of the H3 system is available at the Uber Engeneering site.

h3IsValid

Verifies whether the number is a valid H3 index.

Syntax

h3IsValid(h3index)

Parameter

• h3index — Hexagon index number. Type: UInt64.

Returned values

• 1 — The number is a valid H3 index.
• 0 — The number is not a valid H3 index.

Type: UInt8.

Example

Query:

SELECT h3IsValid(630814730351855103) AS h3IsValid;

Result:

┌─h3IsValid─┐
│         1 │
└───────────┘

h3GetResolution

Defines the resolution of the given H3 index.

Syntax

h3GetResolution(h3index)

Parameter

• h3index — Hexagon index number. Type: UInt64.

Returned values

• Index resolution. Range: [0, 15].
• If the index is not valid, the function returns a random value. Use h3IsValid to verify the index.

Type: UInt8.

Example

Query:

SELECT h3GetResolution(639821929606596015) AS resolution;

Result:

┌─resolution─┐
│         14 │
└────────────┘

h3EdgeAngle

Calculates the average length of the H3 hexagon edge in grades.

Syntax

h3EdgeAngle(resolution)

Parameter

• resolution — Index resolution. Type: UInt8. Range: [0, 15].

Returned values

• The average length of the H3 hexagon edge in grades. Type: Float64.

Example

Query:

SELECT h3EdgeAngle(10) AS edgeAngle;

Result:

┌───────h3EdgeAngle(10)─┐
│ 0.0005927224846720883 │
└───────────────────────┘

h3EdgeLengthM

Calculates the average length of the H3 hexagon edge in meters.

Syntax

h3EdgeLengthM(resolution)

Parameter

• resolution — Index resolution. Type: UInt8. Range: [0, 15].

Returned values

• The average length of the H3 hexagon edge in meters. Type: Float64.

Example

Query:

SELECT h3EdgeLengthM(15) AS edgeLengthM;

Result:

┌─edgeLengthM─┐
│ 0.509713273 │
└─────────────┘

h3EdgeLengthKm

Calculates the average length of the H3 hexagon edge in kilometers.

Syntax

h3EdgeLengthKm(resolution)

Parameter

• resolution — Index resolution. Type: UInt8. Range: [0, 15].

Returned values

• The average length of the H3 hexagon edge in kilometers. Type: Float64.

Example

Query:

SELECT h3EdgeLengthKm(15) AS edgeLengthKm;

Result:

┌─edgeLengthKm─┐
│  0.000509713 │
└──────────────┘

geoToH3

Returns H3 point index (lon, lat) with specified resolution.

Syntax

geoToH3(lon, lat, resolution)

Arguments

• lon — Longitude. Type: Float64.
• lat — Latitude. Type: Float64.
• resolution — Index resolution. Range: [0, 15]. Type: UInt8.

Returned values

• Hexagon index number.
• 0 in case of error.

Type: UInt64.

Example

Query:

SELECT geoToH3(37.79506683, 55.71290588, 15) AS h3Index;

Result:

┌────────────h3Index─┐
│ 644325524701193974 │
└────────────────────┘

h3ToGeo

Returns the centroid longitude and latitude corresponding to the provided H3 index.

Syntax

h3ToGeo(h3Index)

Arguments

• h3Index — H3 Index. UInt64.

Returned values

• A tuple consisting of two values: tuple(lon,lat). lon — Longitude. Float64. lat — Latitude. Float64.

Example

Query:

SELECT h3ToGeo(644325524701193974) AS coordinates;

Result:

┌─coordinates───────────────────────────┐
│ (37.79506616830252,55.71290243145668) │
└───────────────────────────────────────┘

h3ToGeoBoundary

Returns array of pairs (lon, lat), which corresponds to the boundary of the provided H3 index.

Syntax

h3ToGeoBoundary(h3Index)

Arguments

• h3Index — H3 Index. Type: UInt64.

Returned values

• Array of pairs '(lon, lat)'. Type: Array(Float64, Float64).

Example

Query:

SELECT h3ToGeoBoundary(644325524701193974) AS coordinates;

Result:

┌─h3ToGeoBoundary(599686042433355775)────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ [(37.2713558667319,-121.91508032705622),(37.353926450852256,-121.8622232890249),(37.42834118609435,-121.92354999630156),(37.42012867767779,-122.03773496427027),(37.33755608435299,-122.090428929044),(37.26319797461824,-122.02910130919001)] │
└────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘

h3kRing

Lists all the H3 hexagons in the raduis of k from the given hexagon in random order.

Syntax

h3kRing(h3index, k)

Arguments

• h3index — Hexagon index number. Type: UInt64.
• k — Radius. Type: integer

Returned values

• Array of H3 indexes.

Type: Array(UInt64).

Example

Query:

SELECT arrayJoin(h3kRing(644325529233966508, 1)) AS h3index;

Result:

┌────────────h3index─┐
│ 644325529233966508 │
│ 644325529233966497 │
│ 644325529233966510 │
│ 644325529233966504 │
│ 644325529233966509 │
│ 644325529233966355 │
│ 644325529233966354 │
└────────────────────┘

h3GetBaseCell

Returns the base cell number of the H3 index.

Syntax

h3GetBaseCell(index)

Parameter

• index — Hexagon index number. Type: UInt64.

Returned value

• Hexagon base cell number.

Type: UInt8.

Example

Query:

SELECT h3GetBaseCell(612916788725809151) AS basecell;

Result:

┌─basecell─┐
│       12 │
└──────────┘

h3HexAreaM2

Returns average hexagon area in square meters at the given resolution.

Syntax

h3HexAreaM2(resolution)

Parameter

• resolution — Index resolution. Range: [0, 15]. Type: UInt8.

Returned value

• Area in square meters.

Type: Float64.

Example

Query:

SELECT h3HexAreaM2(13) AS area;

Result:

┌─area─┐
│ 43.9 │
└──────┘

h3HexAreaKm2

Returns average hexagon area in square kilometers at the given resolution.

Syntax

h3HexAreaKm2(resolution)

Parameter

• resolution — Index resolution. Range: [0, 15]. Type: UInt8.

Returned value

• Area in square kilometers.

Type: Float64.

Example

Query:

SELECT h3HexAreaKm2(13) AS area;

Result:

┌──────area─┐
│ 0.0000439 │
└───────────┘

h3IndexesAreNeighbors

Returns whether or not the provided H3 indexes are neighbors.

Syntax

h3IndexesAreNeighbors(index1, index2)

Arguments

• index1 — Hexagon index number. Type: UInt64.
• index2 — Hexagon index number. Type: UInt64.

Returned value

• 1 — Indexes are neighbours.
• 0 — Indexes are not neighbours.

Type: UInt8.

Example

Query:

SELECT h3IndexesAreNeighbors(617420388351344639, 617420388352655359) AS n;

Result:

┌─n─┐
│ 1 │
└───┘

h3ToChildren

Returns an array of child indexes for the given H3 index.

Syntax

h3ToChildren(index, resolution)

Arguments

• index — Hexagon index number. Type: UInt64.
• resolution — Index resolution. Range: [0, 15]. Type: UInt8.

Returned values

• Array of the child H3-indexes.

Type: Array(UInt64).

Example

Query:

SELECT h3ToChildren(599405990164561919, 6) AS children;

Result:

┌─children───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ [603909588852408319,603909588986626047,603909589120843775,603909589255061503,603909589389279231,603909589523496959,603909589657714687] │
└────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘

h3ToParent

Returns the parent (coarser) index containing the given H3 index.

Syntax

h3ToParent(index, resolution)

Arguments

• index — Hexagon index number. Type: UInt64.
• resolution — Index resolution. Range: [0, 15]. Type: UInt8.

Returned value

• Parent H3 index.

Type: UInt64.

Example

Query:

SELECT h3ToParent(599405990164561919, 3) AS parent;

Result:

┌─────────────parent─┐
│ 590398848891879423 │
└────────────────────┘

h3ToString

Converts the H3Index representation of the index to the string representation.

h3ToString(index)

Parameter

• index — Hexagon index number. Type: UInt64.

Returned value

• String representation of the H3 index.

Type: String.

Example

Query:

SELECT h3ToString(617420388352917503) AS h3_string;

Result:

┌─h3_string───────┐
│ 89184926cdbffff │
└─────────────────┘

stringToH3

Converts the string representation to the H3Index (UInt64) representation.

Syntax

stringToH3(index_str)

Parameter

• index_str — String representation of the H3 index. Type: String.

Returned value

• Hexagon index number. Returns 0 on error. Type: UInt64.

Example

Query:

SELECT stringToH3('89184926cc3ffff') AS index;

Result:

┌──────────────index─┐
│ 617420388351344639 │
└────────────────────┘

h3GetResolution

Returns the resolution of the H3 index.

Syntax

h3GetResolution(index)

Parameter

• index — Hexagon index number. Type: UInt64.

Returned value

• Index resolution. Range: [0, 15]. Type: UInt8.

Example

Query:

SELECT h3GetResolution(617420388352917503) AS res;

Result:

┌─res─┐
│   9 │
└─────┘

h3IsResClassIII

Returns whether H3 index has a resolution with Class III orientation.

Syntax

h3IsResClassIII(index)

Parameter

• index — Hexagon index number. Type: UInt64.

Returned value

• 1 — Index has a resolution with Class III orientation.
• 0 — Index doesn't have a resolution with Class III orientation.

Type: UInt8.

Example

Query:

SELECT h3IsResClassIII(617420388352917503) AS res;

Result:

┌─res─┐
│   1 │
└─────┘

h3IsPentagon

Returns whether this H3 index represents a pentagonal cell.

Syntax

h3IsPentagon(index)

Parameter

• index — Hexagon index number. Type: UInt64.

Returned value

• 1 — Index represents a pentagonal cell.
• 0 — Index doesn't represent a pentagonal cell.

Type: UInt8.

Example

Query:

SELECT h3IsPentagon(644721767722457330) AS pentagon;

Result:

┌─pentagon─┐
│        0 │
└──────────┘

h3GetFaces

Returns icosahedron faces intersected by a given H3 index.

Syntax

h3GetFaces(index)

Parameter

• index — Hexagon index number. Type: UInt64.

Returned values

• Array containing icosahedron faces intersected by a given H3 index.

Type: Array(UInt64).

Example

Query:

SELECT h3GetFaces(599686042433355775) AS faces;

Result:

┌─faces─┐
│ [7]   │
└───────┘

h3CellAreaM2

Returns the exact area of a specific cell in square meters corresponding to the given input H3 index.

Syntax

h3CellAreaM2(index)

Parameter

• index — Hexagon index number. Type: UInt64.

Returned value

• Cell area in square meters.

Type: Float64.

Example

Query:

SELECT h3CellAreaM2(579205133326352383) AS area;

Result:

┌───────────────area─┐
│ 4106166334463.9233 │
└────────────────────┘

h3CellAreaRads2

Returns the exact area of a specific cell in square radians corresponding to the given input H3 index.

Syntax

h3CellAreaRads2(index)

Parameter

• index — Hexagon index number. Type: UInt64.

Returned value

• Cell area in square radians.

Type: Float64.

Example

Query:

SELECT h3CellAreaRads2(579205133326352383) AS area;

Result:

┌────────────────area─┐
│ 0.10116268528089567 │
└─────────────────────┘

h3ToCenterChild

Returns the center child (finer) H3 index contained by given H3 at the given resolution.

Syntax

h3ToCenterChild(index, resolution)

Parameter

• index — Hexagon index number. Type: UInt64.
• resolution — Index resolution. Range: [0, 15]. Type: UInt8.

Returned values

• H3 index of the center child contained by given H3 at the given resolution.

Type: UInt64.

Example

Query:

SELECT h3ToCenterChild(577023702256844799,1) AS centerToChild;

Result:

┌──────centerToChild─┐
│ 581496515558637567 │
└────────────────────┘

h3ExactEdgeLengthM

Returns the exact edge length of the unidirectional edge represented by the input h3 index in meters.

Syntax

h3ExactEdgeLengthM(index)

Parameter

• index — Hexagon index number. Type: UInt64.

Returned value

• Exact edge length in meters.

Type: Float64.

Example

Query:

SELECT h3ExactEdgeLengthM(1310277011704381439) AS exactEdgeLengthM;;

Result:

┌───exactEdgeLengthM─┐
│ 195449.63163407316 │
└────────────────────┘

h3ExactEdgeLengthKm

Returns the exact edge length of the unidirectional edge represented by the input h3 index in kilometers.

Syntax

h3ExactEdgeLengthKm(index)

Parameter

• index — Hexagon index number. Type: UInt64.

Returned value

• Exact edge length in kilometers.

Type: Float64.

Example

Query:

SELECT h3ExactEdgeLengthKm(1310277011704381439) AS exactEdgeLengthKm;;

Result:

┌──exactEdgeLengthKm─┐
│ 195.44963163407317 │
└────────────────────┘

h3ExactEdgeLengthRads

Returns the exact edge length of the unidirectional edge represented by the input h3 index in radians.

Syntax

h3ExactEdgeLengthRads(index)

Parameter

• index — Hexagon index number. Type: UInt64.

Returned value

• Exact edge length in radians.

Type: Float64.

Example

Query:

SELECT h3ExactEdgeLengthRads(1310277011704381439) AS exactEdgeLengthRads;;

Result:

┌──exactEdgeLengthRads─┐
│ 0.030677980118976447 │
└──────────────────────┘

h3NumHexagons

Returns the number of unique H3 indices at the given resolution.

Syntax

h3NumHexagons(resolution)

Parameter

• resolution — Index resolution. Range: [0, 15]. Type: UInt8.

Returned value

• Number of H3 indices.

Type: Int64.

Example

Query:

SELECT h3NumHexagons(3) AS numHexagons;

Result:

┌─numHexagons─┐
│       41162 │
└─────────────┘

h3Line

Returns the line of indices between the two indices that are provided.

Syntax

h3Line(start,end)

Parameter

• start — Hexagon index number that represents a starting point. Type: UInt64.
• end — Hexagon index number that represents an ending point. Type: UInt64.

Returned value

Array of h3 indexes representing the line of indices between the two provided indices:

Type: Array(UInt64).

Example

Query:

 SELECT h3Line(590080540275638271,590103561300344831) as indexes;

Result:

┌─indexes────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ [590080540275638271,590080471556161535,590080883873021951,590106516237844479,590104385934065663,590103630019821567,590103561300344831] │
└────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘

h3Distance

Returns the distance in grid cells between the two indices that are provided.

Syntax

h3Distance(start,end)

Parameter

• start — Hexagon index number that represents a starting point. Type: UInt64.
• end — Hexagon index number that represents an ending point. Type: UInt64.

Returned value

• Number of grid cells.

Type: Int64.

Returns a negative number if finding the distance fails.

Example

Query:

 SELECT h3Distance(590080540275638271,590103561300344831) as distance;

Result:

┌─distance─┐
│        7 │
└──────────┘

h3HexRing

Returns the indexes of the hexagonal ring centered at the provided origin h3Index and length k.

Returns 0 if no pentagonal distortion was encountered.

Syntax

h3HexRing(index, k)

Parameter

• index — Hexagon index number that represents the origin. Type: UInt64.
• k — Distance. Type: UInt64.

Returned values

• Array of H3 indexes.

Type: Array(UInt64).

Example

Query:

 SELECT h3HexRing(590080540275638271, toUInt16(1)) AS hexRing;

Result:

┌─hexRing─────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ [590080815153545215,590080471556161535,590080677714591743,590077585338138623,590077447899185151,590079509483487231] │
└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘

Original article