Documentation

geo.gridFilter() function

The geo.gridFilter() function is experimental and subject to change at any time. By using this function, you accept the risks of experimental functions.

The geo.gridFilter() function filters data by a specified geographic region. It compares input data to a set of S2 Cell ID tokens located in the specified region.

S2 Grid cells may not perfectly align with the defined region, so results may include data with coordinates outside the region, but inside S2 grid cells partially covered by the region. Use toRows() and geo.strictFilter() after geo.gridFilter() to precisely filter points. See Non-strict and strict filtering below.

Function type: Transformation

import "experimental/geo"

geo.gridFilter(
  region: {lat: 40.69335938, lon: -73.30078125, radius: 20.0}
  minSize: 24,
  maxSize: -1,
  level: -1,
  s2cellIDLevel: -1
)

s2_cell_id must be part of the group key

To filter geo-temporal data with geo.gridFilter(), s2_cell_id must be part of the group key. To add s2_cell_id to the group key, use experimental.group:

import "experimental"

// ...
  |> experimental.group(columns: ["s2_cell_id"], mode: "extend")

Non-strict and strict filtering

In most cases, the specified geographic region does not perfectly align with S2 grid cells.

  • Non-strict filtering returns points that may be outside of the specified region but inside S2 grid cells partially covered by the region.
  • Strict filtering returns only points inside the specified region.

S2 grid cell
Filter region
Returned point

Non-strict filtering

Strict filtering

Parameters

region

The region containing the desired data points. Specify record properties for the shape. See Region definitions.

Data type: Record

minSize

Minimum number of cells that cover the specified region. Default is 24.

Data type: Integer

maxSize

Maximum number of cells that cover the specified region. Default is -1.

Data type: Integer

level

S2 cell level of grid cells. Default is -1.

Data type: Integer

level is mutually exclusive with minSize and maxSize and must be less than or equal to s2cellIDLevel.

s2cellIDLevel

S2 Cell level used in s2_cell_id tag. Default is -1.

Data type: Integer

When set to -1, gridFilter() attempts to automatically detect the S2 Cell ID level.

Examples

Filter data in a box-shaped region
import "experimental/geo"

from(bucket: "example-bucket")
  |> range(start: -1h)
  |> filter(fn: (r) => r._measurement == "example-measurement")
  |> geo.gridFilter(
    region: {
      minLat: 40.51757813,
      maxLat: 40.86914063,
      minLon: -73.65234375,
      maxLon: -72.94921875
    }
  )
Filter data in a circular region
import "experimental/geo"

from(bucket: "example-bucket")
  |> range(start: -1h)
  |> filter(fn: (r) => r._measurement == "example-measurement")
  |> geo.gridFilter(
    region: {
      lat: 40.69335938,
      lon: -73.30078125,
      radius: 20.0
    }
  )
Filter data in a custom polygon region
import "experimental/geo"

from(bucket: "example-bucket")
  |> range(start: -1h)
  |> filter(fn: (r) => r._measurement == "example-measurement")
  |> geo.gridFilter(
    region: {
      points: [
        {lat: 40.671659, lon: -73.936631},
        {lat: 40.706543, lon: -73.749177},
        {lat: 40.791333, lon: -73.880327}
      ]
    }
  )

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