Beskrivning

Returns a simplified representation of a geometry using the Visvalingam-Whyatt algorithm. The simplification tolerance is an area value, in squared units of the input SRS. Simplification removes vertices which form "corners" with area less than the tolerance. The result may not be valid even if the input is.

Funktionen kan anropas med alla typer av geometri (inklusive GeometryCollections), men endast linje- och polygonelement förenklas. Ändpunkter för linjär geometri bevaras.

	Den returnerade geometrin kan förlora sin enkelhet (se ST_IsSimple), topologin kanske inte bevaras och polygonala resultat kan vara ogiltiga (se ST_IsValid). Använd ST_SimplifyPreserveTopology för att bevara topologin och säkerställa giltigheten. ST_CoverageSimplify bevarar också topologin och giltigheten.

This is a general-purpose simplification function. It may remove narrow polygon spikes when their effective area is below the tolerance, but it is not a dedicated spike-removal or polygon-repair operation. Use ST_IsValid to check the result and ST_MakeValid to repair invalid polygonal output if needed.

Denna funktion bevarar inte gränser som delas mellan polygoner. Använd ST_CoverageSimplify om detta krävs.

Denna funktion hanterar 3D och den tredje dimensionen kommer att påverka resultatet.

Tillgänglighet: 2.2.0

Exempel

This polygon has a narrow spike whose effective area is small enough to be removed by a tolerance of 20 square units.

SELECT geom AS original, ST_SimplifyVW(geom, 20) AS simplified
FROM (SELECT 'POLYGON((0 0,10 0,10 10,5.2 10,5 16,4.8 10,0 10,0 0))'::geometry AS geom) AS t;

POLYGON((0 0,10 0,10 10,5.2 10,5 16,4.8 10,0 10,0 0)) | POLYGON((0 0,10 0,10 10,0 10,0 0))

01030000000100000008000000000000000000000000000000000000000000000000002440000000000000000000000000000024400000000000002440CDCCCCCCCCCC1440000000000000244000000000000014400000000000003040333333333333134000000000000024400000000000000000000000000000244000000000000000000000000000000000 | 010300000001000000050000000000000000000000000000000000000000000000000024400000000000000000000000000000244000000000000024400000000000000000000000000000244000000000000000000000000000000000

Figure

A LineString is simplified with a minimum-area tolerance of 30. For a linear simplification using ST_Simplify, a comparable tolerance would be a length in input-SRS units, so the value here is roughly that linear tolerance squared.

SELECT ST_SimplifyVW(geom, 30) simplified
  FROM (SELECT 'LINESTRING(5 2,3 8,6 20,7 25,10 10)'::geometry AS geom) AS t;

LINESTRING(5 2,7 25,10 10)

010200000003000000000000000000144000000000000000400000000000001C40000000000000394000000000000024400000000000002440

Figure

Förenkling av en linje.

SELECT ST_SimplifyVW('LINESTRING (10 10,50 40,30 70,50 60,70 80,50 110,100 100,90 140,100 180,150 170,170 140,190 90,180 40,110 40,150 20)'::geometry,
1600);

LINESTRING(10 10,100 100,100 180,150 170,190 90,150 20)

0102000000060000000000000000002440000000000000244000000000000059400000000000005940000000000000594000000000008066400000000000C0624000000000004065400000000000C0674000000000008056400000000000C062400000000000003440

Figure

Förenkling av en polygon.

SELECT ST_SimplifyVW('POLYGON ((20 20,50 60,20 120,40 170,80 180,120 140,180 180,160 130,180 100,180 30,130 70,150 10,20 20))'::geometry,
1600);

POLYGON((20 20,20 120,80 180,160 130,180 30,20 20))

010300000001000000060000000000000000003440000000000000344000000000000034400000000000005E40000000000000544000000000008066400000000000006440000000000040604000000000008066400000000000003E4000000000000034400000000000003440

Figure

Se även

ST_SetEffectiveArea, ST_Simplify, ST_SimplifyPreserveTopology, ST_CoverageSimplify, Topologi ST_Simplify