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 │
└─────────────┘

geoToH3 

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

Syntax

geoToH3(lon, lat, resolution)

Parameters

  • 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 │
└────────────────────┘

h3kRing 

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

Syntax

h3kRing(h3index, k)

Parameters

  • h3index — Hexagon index number. Type: UInt64.
  • k — Raduis. 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 │
└──────┘

h3IndexesAreNeighbors 

Returns whether or not the provided H3 indexes are neighbors.

Syntax

h3IndexesAreNeighbors(index1, index2)

Parameters

  • 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)

Parameters

  • 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)

Parameters

  • 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 │
└─────┘

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