# s2
[S2](https://s2geometry.io/) is a library for spherical geometry that aims to have the same robustness, flexibility, and performance as the very best planar geometry libraries.
You can learn more about S2 in the [Spatial Indexes section](https://docs.carto.com/data-and-analysis/analytics-toolbox-for-redshift/key-concepts/spatial-indexes#s2) of the documentation.
## S2\_BOUNDARY
```sql
S2_BOUNDARY(id)
```
**Description**
Returns the boundary for a given S2 Cell ID as a WKT string. Note that S2 cell vertices should be joined with geodesic edges (great circles), not straight lines in a planar projection.
**Input parameters**
* `id`: `INT8` id to get the boundary geography from.
**Return type**
`VARCHAR(MAX)`
**Example**
{% code overflow="wrap" lineNumbers="true" %}
```sql
SELECT carto.S2_BOUNDARY(955378847514099712);
-- POLYGON ((-3.74350899127 40.2485011413, -3.41955272426 40.2585007122, -3.41955272426 40.5842313862, -3.74350899127 40.5742134506, -3.74350899127 40.2485011413))
```
{% endcode %}
## S2\_FROMGEOGPOINT
```sql
S2_FROMGEOGPOINT(point, resolution)
```
**Description**
Returns the S2 cell ID of a given point at a requested resolution.
**Input parameters**
* `point`: `GEOGRAPHY` vertical coordinate of the map.
* `resolution`: `INT4` level of detail or zoom.
**Return type**
`INT8`
**Example**
{% code overflow="wrap" lineNumbers="true" %}
```sql
SELECT carto.S2_FROMGEOGPOINT(ST_POINT(-3.7038, 40.4168), 8);
-- 955378847514099712
```
{% endcode %}
## S2\_FROMHILBERTQUADKEY
```sql
S2_FROMHILBERTQUADKEY(hquadkey)
```
**Description**
Returns the conversion of a Hilbert quadkey (a.k.a Hilbert curve quadtree ID) into a S2 cell ID.
**Input parameters**
* `hquadkey`: `VARCHAR(MAX)` Hilbert quadkey to be converted.
**Return type**
`INT8`
**Example**
{% code overflow="wrap" lineNumbers="true" %}
```sql
SELECT carto.S2_FROMHILBERTQUADKEY('0/12220101');
-- 955378847514099712
```
{% endcode %}
## S2\_FROMLONGLAT
```sql
S2_FROMLONGLAT(longitude, latitude, resolution)
```
**Description**
Returns the S2 cell ID representation for a requested resolution and geographic coordinates.
**Input parameters**
* `longitude`: `FLOAT8` horizontal coordinate of the map.
* `latitude`: `FLOAT8` vertical coordinate of the map.
* `resolution`: `INT4` level of detail or zoom.
**Return type**
`INT8`
**Example**
{% code overflow="wrap" lineNumbers="true" %}
```sql
SELECT carto.S2_FROMLONGLAT(-3.7038, 40.4168, 8);
-- 955378847514099712
```
{% endcode %}
## S2\_FROMTOKEN
```sql
S2_FROMTOKEN(token)
```
**Description**
Returns the conversion of an S2 cell token (hexified ID) into an unsigned, 64 bit ID.
**Input parameters**
* `token`: `VARCHAR(MAX)` S2 cell token.
**Return type**
`INT8`
**Example**
{% code overflow="wrap" lineNumbers="true" %}
```sql
SELECT carto.S2_FROMTOKEN('0d423');
-- 955378847514099712
```
{% endcode %}
## S2\_FROMUINT64REPR
```sql
S2_FROMUINT64REPR(uid)
```
**Description**
Returns an INT64 cell ID from its UINT64 representation.
**Input parameters**
* `uid`: `VARCHAR(MAX)` UINT64 representation of a S2 cell ID.
**Return type**
`INT8`
**Example**
{% code overflow="wrap" lineNumbers="true" %}
```sql
SELECT carto.S2_FROMUINT64REPR('9926595690882924544');
-- -8520148382826627072
```
{% endcode %}
## S2\_POLYFILL\_BBOX
```sql
S2_POLYFILL_BBOX(min_longitude, max_longitude, min_latitude, max_latitude [, min_resolution, max_resolution])
```
**Description**
Returns a SUPER containing an array of S2 cell IDs that cover a planar bounding box. Note that this is a compact coverage (polyfill), so the bounding box is covered with the least amount of cells by using the largest cells possible.
Two optional arguments can be passed with the minimum and maximum resolution for coverage. If you desire a coverage at a single resolution level, simply set the maximum and minimum longitude to be of equal value.
**Input parameters**
* `min_longitude`: `FLOAT8` minimum longitude of the bounding box.
* `max_longitude`: `FLOAT8` maximum longitude of the bounding box.
* `min_latitude`: `FLOAT8` minimum latitude of the bounding box.
* `max_latitude`: `FLOAT8` maximum latitude of the bounding box.
* `min_resolution` (optional): `INT4` minimum resolution level for cells covering the bounding box. Defaults to `0`.
* `max_resolution` (optional): `INT4` maximum resolution level for cells covering the bounding box. Defaults to `30`.
**Return type**
`SUPER`
**Example**
{% code overflow="wrap" lineNumbers="true" %}
```sql
SELECT carto.S2_POLYFILL_BBOX(-3.688531, -3.680077, 40.409771, 40.421501);
-- [955367986615549952,955367988763033600,955367994131742720,955368019096240128,
-- 955368020975288320,955370721435975680,955370742910812160,955370751500746752]
SELECT carto.S2_POLYFILL_BBOX(-3.688531, -3.680077, 40.409771, 40.421501, 4, 8);
-- [955378847514099712]
-- Single level coverage
SELECT carto.S2_POLYFILL_BBOX(-3.688531, -3.680077, 40.409771, 40.421501, 12, 12);
-- [955367921117298688,955368058556252160,955370669896368128,955370807335321600]
```
{% endcode %}
## S2\_RESOLUTION
```sql
S2_RESOLUTION(id)
```
**Description**
Returns an integer with the resolution of a given cell ID.
**Input parameters**
* `id`: `INT8` id to get the resolution from.
**Return type**
`INT4`
**Example**
{% code overflow="wrap" lineNumbers="true" %}
```sql
SELECT carto.S2_RESOLUTION(955378847514099712);
-- 8
```
{% endcode %}
## S2\_TOCHILDREN
```sql
S2_TOCHILDREN(id [, resolution])
```
**Description**
Returns a SUPER containing a plain array of children IDs of a given cell ID for a specific resolution. A child is an S2 cell of higher level of detail that is contained within the current cell. Each cell has four direct children by definition.
By default, this function returns the direct children (where parent resolution is children resolution - 1). However, an optional resolution argument can be passed with the desired parent resolution. Note that the amount of children grows to the power of four per zoom level.
**Input parameters**
* `id`: `INT8` id to get the children from.
* `resolution` (optional): `INT4` resolution of the desired children.
**Return type**
`SUPER`
**Example**
{% code overflow="wrap" lineNumbers="true" %}
```sql
SELECT carto.S2_TOCHILDREN(955378847514099712);
-- 955365653374566400
-- 955374449467588608
-- 955383245560610816
-- 955392041653633024
SELECT carto.S2_TOCHILDREN(955378847514099712, 9);
-- 955365653374566400
-- 955374449467588608
-- 955383245560610816
-- 955392041653633024
```
{% endcode %}
## S2\_TOHILBERTQUADKEY
```sql
S2_TOHILBERTQUADKEY(id)
```
**Description**
Returns the conversion of a S2 cell ID into a Hilbert quadkey (a.k.a Hilbert curve quadtree ID).
**Input parameters**
* `id`: `INT8` S2 cell ID to be converted.
**Return type**
`VARCHAR(MAX)`
**Example**
{% code overflow="wrap" lineNumbers="true" %}
```sql
SELECT carto.S2_TOHILBERTQUADKEY(955378847514099712);
-- 0/12220101
```
{% endcode %}
## S2\_TOPARENT
```sql
S2_TOPARENT(id, resolution)
```
**Description**
Returns the parent ID of a given cell ID for a specific resolution. A parent cell is the smaller resolution containing cell.
By default, this function returns the direct parent (where parent resolution is child resolution + 1). However, an optional resolution argument can be passed with the desired parent resolution.
**Input parameters**
* `id`: `INT8` quadint to get the parent from.
* `resolution` (optional): `INT4` resolution of the desired parent.
**Return type**
`INT8`
**Example**
{% code overflow="wrap" lineNumbers="true" %}
```sql
SELECT carto.S2_TOPARENT(955378847514099712);
-- 955396439700144128
SELECT carto.S2_TOPARENT(955378847514099712, 1);
-- 864691128455135232
```
{% endcode %}
## S2\_TOTOKEN
```sql
S2_TOTOKEN(id)
```
**Description**
Returns the conversion of a S2 cell ID into a token (S2 cell hexified ID).
**Input parameters**
* `id`: `INT8` S2 cell ID.
**Return type**
`VARCHAR(MAX)`
**Example**
{% code overflow="wrap" lineNumbers="true" %}
```sql
SELECT carto.S2_TOTOKEN(955378847514099712);
-- 0d423
```
{% endcode %}
## S2\_TOUINT64REPR
```sql
S2_TOUINT64REPR(id)
```
**Description**
Returns the UINT64 representation of a cell ID.
**Input parameters**
* `id`: `INT8` S2 cell ID.
**Return type**
`VARCHAR(MAX)`
**Example**
{% code overflow="wrap" lineNumbers="true" %}
```sql
SELECT carto.S2_TOUINT64REPR(-8520148382826627072);
-- 9926595690882924544
```
{% endcode %}