6.7 KiB
| toc_title |
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| S2 Geometry |
Functions for Working with S2 Index
S2 is a geographical indexing system where all geographical data is represented on a three-dimensional sphere (similar to a globe).
geoToS2
Returns S2 point index corresponding to the provided coordinates (longitude, latitude).
Syntax
geoToS2(lon, lat)
Arguments
Returned values
- S2 point index.
Type: UInt64.
Example
Query:
SELECT geoToS2(37.79506683, 55.71290588) as s2Index;
Result:
┌─────────────s2Index─┐
│ 4704772434919038107 │
└─────────────────────┘
s2ToGeo
Returns geo coordinates (longitude, latitude) corresponding to the provided S2 point index.
Syntax
s2ToGeo(s2index)
Arguments
s2Index— S2 Index. UInt64.
Returned values
- A tuple consisting of two values:
tuple(lon,lat).
Type: lon - Float64. lat — Float64.
Example
Query:
SELECT s2ToGeo(4704772434919038107) as s2Coodrinates;
Result:
┌─s2Coodrinates────────────────────────┐
│ (37.79506681471008,55.7129059052841) │
└──────────────────────────────────────┘
s2GetNeighbors
Returns S2 neighbor indices corresponding to the provided S2). Each cell in the S2 system is a quadrilateral bounded by four geodesics. So, each cell has 4 neighbors.
Syntax
s2ToGeo(s2index)
Arguments
s2index— S2 Index. UInt64.
Returned values
- An array consisting of the 4 neighbor indices:
array[s2index1, s2index3, s2index2, s2index4].
Type: Each S2 index is UInt64.
Example
Query:
select s2GetNeighbors(5074766849661468672) AS s2Neighbors;
Result:
┌─s2Neighbors───────────────────────────────────────────────────────────────────────┐
│ [5074766987100422144,5074766712222515200,5074767536856236032,5074767261978329088] │
└───────────────────────────────────────────────────────────────────────────────────┘
s2CellsIntersect
Determines if the two provided S2) cell indices intersect or not.
Syntax
s2CellsIntersect(s2index1, s2index2)
Arguments
siIndex1,s2index2— S2 Index. UInt64.
Returned values
- 1 — If the S2 cell indices intersect.
- 0 — If the S2 cell indices don't intersect.
Type: UInt8.
Example
Query:
select s2CellsIntersect(9926595209846587392, 9926594385212866560) as intersect;
Result:
┌─intersect─┐
│ 1 │
└───────────┘
s2CapContains
A cap represents a portion of the sphere that has been cut off by a plane. It is defined by a point on a sphere and a radius in degrees. Imagine that we draw a line through the center of the sphere and our point. An infinite number of planes pass through this line, but any plane will intersect the cap in two points. Thus the angle is defined by one of this points and the entire line. So, the radius of Pi/2 defines a hemisphere and the radius of Pi defines a whole sphere.
Determines if a cap contains a s2 point index.
Syntax
s2CellsIntersect(center, degrees, point)
Arguments
center- S2 point index corresponding to the cap. UInt64.degrees- Radius of the cap in degrees. Float64.point- S2 point index. UInt64.
Returned values
- 1 — If the cap contains the S2 point index.
- 0 — If the cap doesn't contain the S2 point index.
Type: UInt8.
Example
Query:
select s2CapContains(1157339245694594829, 1.0, 1157347770437378819) as capContains;
Result:
┌─capContains─┐
│ 1 │
└─────────────┘
s2CapUnion
A cap represents a portion of the sphere that has been cut off by a plane. It is defined by a point on a sphere and a radius in degrees. Imagine that we draw a line through the center of the sphere and our point. An infinite number of planes pass through this line, but any plane will intersect the cap in two points. Thus the angle is defined by one of this points and the entire line. So, the radius of Pi/2 defines a hemisphere and the radius of Pi defines a whole sphere.
Determines the smallest cap that contains the given two input caps.
Syntax
s2CapUnion(center1, radius1, center2, radius2)
Arguments
center1,center2- S2 point indices corresponding to the two input caps. UInt64.radius1,radius2- Radii of the two input caps in degrees. Float64.
Returned values
center- S2 point index corresponding the center of the smallest cap containing the two input caps. Type: UInt64.radius- Radius of the smallest cap containing the two input caps. Type: Float64.
Example
Query:
SELECT s2CapUnion(3814912406305146967, 1.0, 1157347770437378819, 1.0) AS capUnion;
Result:
┌─capUnion───────────────────────────────┐
│ (4534655147792050737,60.2088283994957) │
└────────────────────────────────────────┘