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ST_TriangleContouring

Signatures

-- Return type: tableName[THE_GEOM, IDISO]
ST_TriangleContouring(VARCHAR tableName,
                      INT varArgs1, INT varArgs2, INT varArgs3, ...);
ST_TriangleContouring(VARCHAR tableName,
                      VARCHAR z1, VARCHAR z2, VARCHAR z3,
                      INT varArgs1, INT varArgs2, INT varArgs3, ...);

Description

Splits the triangles contained in table tableName into smaller triangles according to certain z-values with respect to the classes given by the various varArgs arguments. Throws an error if a Geometry is found which is not a triangle.

If column names z1, z2 and z3 are not specified, the z-values of each Geometry (in order of appearance) are used. Otherwise, the values contained in these columns are used.

The various varArgs arguments (you may provide as many as you like) define the classes according to which the triangles are split. The interval from negative infinity to varArgs1 is assigned an IDISO of 0, from varArgs1 to varArgs2 gets an IDISO of 1, etc.

Examples

CREATE TABLE TIN(THE_GEOM GEOMETRY) AS
    SELECT 'POLYGON((0 0 1, 3 0 0, 3 3 4, 0 0 1))';
SELECT * FROM ST_TriangleContouring('TIN', 2, 3, 4);
-- Answer:
-- |                    THE_GEOM                   | IDISO |
-- | --------------------------------------------- | ----- |
-- | POLYGON((3 1.5 2, 1 1 2, 0 0 1, 3 1.5 2))     |     0 |
-- | POLYGON((3 1.5 2, 0 0 1, 3 0 0, 3 1.5 2))     |     0 |
-- | POLYGON((3 2.25 3, 2 2 3, 3 1.5 2, 3 2.25 3)) |     1 |
-- | POLYGON((2 2 3, 1 1 2, 3 1.5 2, 2 2 3))       |     1 |
-- | POLYGON((3 2.25 3, 3 3 4, 2 2 3, 3 2.25 3))   |     2 |

-- In this example, the bottom right corner of the triangle is
-- deleted since it is assigned a z-value (of 6) which is greater
-- than the largest class value (5).
DROP TABLE IF EXISTS TIN;
CREATE TABLE TIN(THE_GEOM GEOMETRY, M1 DOUBLE, M2 INT, M3 DOUBLE) AS
    SELECT 'POLYGON((0 0 1, 3 0 0, 3 3 4, 0 0 1))',
           1.0, 6, 4.0;
SELECT * FROM ST_TriangleContouring('TIN', 'm1', 'm2', 'm3', 2, 3, 5);
-- Answer:
-- |               THE_GEOM               |  m1 |  m2 |  m3 | IDISO |
-- | ------------------------------------ | --- | --- | --- | ----- |
-- | POLYGON((0.6 0 0.8, 1 1 2, 0 0 1,    | 1.0 |   6 | 4.0 |     0 |
-- |          0.6 0 0.8))                 |     |     |     |       |
-- | POLYGON((1.8 1.5 2.4, 2 2 3,         | 1.0 |   6 | 4.0 |     1 |
-- |          0.6 0 0.8, 1.8 1.5 2.4))    |     |     |     |       |
-- | POLYGON((2 2 3, 1 1 2, 0.6 0 0.8,    | 1.0 |   6 | 4.0 |     1 |
-- |          2 2 3))                     |     |     |     |       |
-- | POLYGON((1.2 0 0.6, 1.8 1.5 2.4,     | 1.0 |   6 | 4.0 |     1 |
-- |          0.6 0 0.8, 1.2 0 0.6))      |     |     |     |       |
-- | POLYGON((1.8 1.5 2.4, 3 3 4, 2 2 3,  | 1.0 |   6 | 4.0 |     2 |
-- |          1.8 1.5 2.4))               |     |     |     |       |
-- | POLYGON((1.2 0 0.6, 3 3 4,           | 1.0 |   6 | 4.0 |     2 |
-- |          1.8 1.5 2.4, 1.2 0 0.6))    |     |     |     |       |
-- | POLYGON((2.4 0 0.2, 3 1.5 2,         | 1.0 |   6 | 4.0 |     2 |
-- |          1.2 0 0.6, 2.4 0 0.2))      |     |     |     |       |
-- | POLYGON((3 1.5 2, 3 3 4, 1.2 0 0.6,  | 1.0 |   6 | 4.0 |     2 |
-- |          3 1.5 2))                   |     |     |     |       |

-- An error is thrown if the Geometry is not a triangle.
CREATE TABLE TIN(THE_GEOM GEOMETRY) AS
    SELECT 'POLYGON((0 0 1, 3 0 0, 3 3 4, 0 3 1, 0 0 1))';
SELECT * FROM ST_TriangleContouring('TIN', 2, 3, 4);
-- Answer: Invalid geometry input, got
--         POLYGON ((0 0, 3 0, 3 3, 0 3, 0 0))

See also