crankshaft/doc/08_interpolation.md

Spacial interpolation

Function to interpolate a numeric attribute of a point in a scatter dataset of points, using one of three methos:

• Nearest neighbor(s)
• Barycentric
• IDW

CDB_SpatialInterpolation (query text, point geometry, method integer DEFAULT 1, p1 integer DEFAULT 0, ps integer DEFAULT 0)

Arguments

Name	Type	Description
query	text	query that returns at least the_geom and a numeric value as attrib
point	geometry	The target point to calc the value
method	integer	0:nearest neighbor, 1: barycentric, 2: IDW
p1	integer	limit the number of neighbors, IDW: 0->no limit, NN: 0-> closest one
p2	integer	IDW: order of distance decay, 0-> order 1

CDB_SpatialInterpolation (geom geometry[], values numeric[], point geometry, method integer DEFAULT 1, p1 integer DEFAULT 0, ps integer DEFAULT 0)

Arguments

Name	Type	Description
geom	geometry[]	Array of points's geometries
values	numeric[]	Array of points' values for the param under study
point	geometry	The target point to calc the value
method	integer	0:nearest neighbor, 1: barycentric, 2: IDW
p1	integer	limit the number of neighbors, IDW: 0->no limit, NN: 0-> closest one
p2	integer	IDW: order of distance decay, 0-> order 1

Returns

Column Name	Type	Description
value	numeric	Interpolated value at the given point, -888.888 if the given point is out of the boundaries of the source points set

Default values:

• -888.888: when using Barycentric, the target point is out of the realm of the input points
• -777.777: asking for a method not available

Example Usage

WITH a as (
    SELECT
        array_agg(the_geom) as geomin,
        array_agg(temp::numeric) as colin
    FROM table_4804232032
)
SELECT
    cdb_crankshaft.CDB_SpatialInterpolation(
        geomin,
        colin,
        CDB_latlng(41.38, 2.15),
        1)
FROM
    a