2016-06-14 23:55:45 +08:00
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## Spacial interpolation
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Function to interpolate a numeric attribute of a point in a scatter dataset of points, using one of three methos:
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2016-09-20 18:57:41 +08:00
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* [Nearest neighbor(s)](https://en.wikipedia.org/wiki/Nearest-neighbor_interpolation)
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2016-06-14 23:55:45 +08:00
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* [Barycentric](https://en.wikipedia.org/wiki/Barycentric_coordinate_system)
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* [IDW](https://en.wikipedia.org/wiki/Inverse_distance_weighting)
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### CDB_SpatialInterpolation (query text, point geometry, method integer DEFAULT 1, p1 integer DEFAULT 0, ps integer DEFAULT 0)
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#### Arguments
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| Name | Type | Description |
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|------|------|-------------|
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| query | text | query that returns at least `the_geom` and a numeric value as `attrib` |
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| point | geometry | The target point to calc the value |
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| method | integer | 0:nearest neighbor, 1: barycentric, 2: IDW|
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2016-09-20 18:57:41 +08:00
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| p1 | integer | limit the number of neighbors, IDW: 0->no limit, NN: 0-> closest one|
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2016-06-14 23:55:45 +08:00
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| p2 | integer | IDW: order of distance decay, 0-> order 1|
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### CDB_SpatialInterpolation (geom geometry[], values numeric[], point geometry, method integer DEFAULT 1, p1 integer DEFAULT 0, ps integer DEFAULT 0)
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#### Arguments
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| Name | Type | Description |
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|------|------|-------------|
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| geom | geometry[] | Array of points's geometries |
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| values | numeric[] | Array of points' values for the param under study|
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| point | geometry | The target point to calc the value |
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| method | integer | 0:nearest neighbor, 1: barycentric, 2: IDW|
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2016-09-20 18:57:41 +08:00
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| p1 | integer | limit the number of neighbors, IDW: 0->no limit, NN: 0-> closest one|
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2016-06-14 23:55:45 +08:00
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| p2 | integer | IDW: order of distance decay, 0-> order 1|
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### Returns
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| Column Name | Type | Description |
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|-------------|------|-------------|
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| value | numeric | Interpolated value at the given point, `-888.888` if the given point is out of the boundaries of the source points set |
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2016-09-21 20:24:35 +08:00
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Default values:
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* -888.888: when using Barycentric, the target point is out of the realm of the input points
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* -777.777: asking for a method not available
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2016-06-14 23:55:45 +08:00
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#### Example Usage
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```sql
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with a as (
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select
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array_agg(the_geom) as geomin,
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array_agg(temp::numeric) as colin
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from table_4804232032
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)
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SELECT CDB_SpatialInterpolation(geomin, colin, CDB_latlng(41.38, 2.15),1) FROM a;
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```
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