Merge pull request #61 from CartoDB/add-interpolation

Add interpolation
2016-06-21 11:59:42 -04:00
parent 01fc2c1dd1 5a2319db72
commit 3c066d65fc
4 changed files with 188 additions and 0 deletions
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+## Spacial interpolation
+
+Function to interpolate a numeric attribute of a point in a scatter dataset of points, using one of three methos:
+
+* [Nearest neighbor](https://en.wikipedia.org/wiki/Nearest-neighbor_interpolation)
+* [Barycentric](https://en.wikipedia.org/wiki/Barycentric_coordinate_system)
+* [IDW](https://en.wikipedia.org/wiki/Inverse_distance_weighting)
+
+### 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     | IDW: limit the number of neighbors, 0->no limit|
+| 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     | IDW: limit the number of neighbors, 0->no limit|
+| 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 |
+
+
+#### Example Usage
+
+```sql
+with a as (
+    select
+        array_agg(the_geom) as geomin,
+        array_agg(temp::numeric) as colin
+    from table_4804232032
+)
+SELECT CDB_SpatialInterpolation(geomin, colin, CDB_latlng(41.38, 2.15),1) FROM a;
+```