crankshaft/doc/19_contour.md

Contour maps

Function to generate a contour map from an scatter dataset of points, using one of these three methods:

• Nearest neighbor
• Barycentric
• IDW

CDB_Contour (geom geometry[], values numeric[], resolution integer, buffer numeric, method, classmethod integer, steps integer)

Arguments

Name	Type	Description
geom	geometry[]	Array of points's geometries
values	numeric[]	Array of points' values for the param under study
buffer	numeric	Value between 0 and 1 for spatial buffer of the set of points
method	integer	0:nearest neighbor, 1: barycentric, 2: IDW
classmethod	integer	0:equals, 1: heads&tails, 2:jenks, 3:quantiles
steps	integer	Number of steps in the classification
resolution	integer	if <= 0: max processing time in seconds (smart resolution) , if >0: resolution in meters

Returns

Returns a table object

Name	Type	Description
the_geom	geometry	Geometries of the classified contour map
avg_value	numeric	Avg value of the area
min_value	numeric	Min value of the area
max_value	numeric	Max value of the areal
bin	integer	Index of the class of the area

Example Usage

WITH a AS (
    SELECT
    ARRAY[800, 700, 600, 500, 400, 300, 200, 100]::numeric[] AS vals,
    ARRAY[ST_GeomFromText('POINT(2.1744 41.403)',4326),ST_GeomFromText('POINT(2.1228 41.380)',4326),ST_GeomFromText('POINT(2.1511 41.374)',4326),ST_GeomFromText('POINT(2.1528 41.413)',4326),ST_GeomFromText('POINT(2.165 41.391)',4326),ST_GeomFromText('POINT(2.1498 41.371)',4326),ST_GeomFromText('POINT(2.1533 41.368)',4326),ST_GeomFromText('POINT(2.131386 41.41399)',4326)] AS g
),
b as(
SELECT
    foo.*
FROM
    a,
    cdb_crankshaft.CDB_contour(a.g, a.vals,  0.0, 1, 3, 5, 60) foo
)
SELECT bin, avg_value from b order by bin;