48 lines
1.9 KiB
Markdown
48 lines
1.9 KiB
Markdown
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## Contour maps
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Function to generate a contour map from an scatter dataset of points, using one of three methos:
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* [Nearest neighbor](https://en.wikipedia.org/wiki/Nearest-neighbor_interpolation)
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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_Contour (geom geometry[], values numeric[], resolution integer, buffer numeric, method, classmethod integer, steps integer)
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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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| resolution | integer | Size in meters of the cells in the grid|
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| buffer | numeric | Value between 0 and 1 for spatial buffer of the set of points
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| method | integer | 0:nearest neighbor, 1: barycentric, 2: IDW|
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| classmethod | integer | 0:equals, 1: heads&tails, 2:jenks, 3:quantiles |
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| steps | integer | Number of steps in the classification|
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### Returns
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Returns a table object
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| Name | Type | Description |
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|------|------|-------------|
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| the_geom | geometry | Geometries of the classified contour map|
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| avg_value | numeric | Avg value of the area|
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| min_value | numeric | Min value of the area|
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| max_value | numeric | Max value of the areal|
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| bin | integer | Index of the class of the area|
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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[800, 700, 600, 500, 400, 300, 200, 100]::numeric[] AS vals,
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ARRAY[ST_GeomFromText('POINT(2.1744 41.403)'),ST_GeomFromText('POINT(2.1228 41.380)'),ST_GeomFromText('POINT(2.1511 41.374)'),ST_GeomFromText('POINT(2.1528 41.413)'),ST_GeomFromText('POINT(2.165 41.391)'),ST_GeomFromText('POINT(2.1498 41.371)'),ST_GeomFromText('POINT(2.1533 41.368)'),ST_GeomFromText('POINT(2.131386 41.41399)')] AS g
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)
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SELECT
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foo.*
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FROM
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a,
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CDB_contour(a.g, a.vals, 500, 0.0, 1,3,5) foo;
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```
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