geo_polygon_to_h3cells()

Converts polygon to H3 cells. This function is a useful geospatial join and visualization tool.

Syntax

geo_polygon_to_h3cells(polygon [, resolution[, radius]])

Parameters

Returns

Array of H3 cell token strings of the same resolution that represet a polygon or a multipolygon. If radius is set to a positive value, then the polygon will be enlarged such that all points within the given radius of the input polygon or multipolygon will be contained inside and the newly calculated polygon that will be converted to H3 cells. If polygon, resolution, radius is invalid, or the cell count exceeds the limit, the query will produce a null result.

Seel also geo_polygon_to_s2cells().

Examples

The following example calculates H3 cells that approximate the polygon.

let polygon = dynamic({"type":"Polygon","coordinates":[[[-3.659,40.553],[-3.913,40.409],[-3.729,40.273],[-3.524,40.440],[-3.659,40.553]]]});
print h3_cells = geo_polygon_to_h3cells(polygon)

Output

The following example demonstrates a multipolygon that consists of H3 cells that approximate the above polygon. Specifing a higher resolution will improve polygon approximation.

let polygon = dynamic({"type":"Polygon","coordinates":[[[-3.659,40.553],[-3.913,40.409],[-3.729,40.273],[-3.524,40.440],[-3.659,40.553]]]});
print h3_cells = geo_polygon_to_h3cells(polygon)
| mv-expand cell = h3_cells to typeof(string) // extract cell to a separate row
| project polygon_cell = geo_h3cell_to_polygon(cell) // convert each cell to a polygon
| project individual_polygon_coordinates = pack_array(polygon_cell.coordinates)
| summarize multipolygon_coordinates = make_list(individual_polygon_coordinates)
| project multipolygon = bag_pack("type","MultiPolygon", "coordinates", multipolygon_coordinates)

Output

The following example return null because the polygon is invalid.

let polygon = dynamic({"type":"Polygon","coordinates":[[[0,0],[1,1]]]});
print is_null = isnull(geo_polygon_to_h3cells(polygon))

Output