ST_Buffer
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名称

ST_Buffer — 计算覆盖距几何体给定距离内所有点的几何体。

大纲

geometry ST_Buffer(geometry g1, float radius_of_buffer, text buffer_style_parameters = '');

geometry ST_Buffer(geometry g1, float radius_of_buffer, integer num_seg_quarter_circle);

geography ST_Buffer(geography g1, float radius_of_buffer, text buffer_style_parameters);

geography ST_Buffer(geography g1, float radius_of_buffer, integer num_seg_quarter_circle);

描述

计算表示与几何/地理距离小于或等于给定距离的所有点的 POLYGON 或 MULTIPOLYGON。 负距离会缩小几何图形而不是扩展它。 负距离可能会完全缩小多边形，在这种情况下返回 POLYGON EMPTY。 对于点和线，负距离始终返回空结果。

对于几何体，距离以几何体的空间参考系的单位指定。 对于地理，距离以米为单位指定。

可选的第三个参数控制缓冲区的精度和样式。 缓冲区中圆弧的精度指定为用于近似四分之一圆的线段数（默认值为 8）。 可以通过提供空白分隔的键=值对列表来指定缓冲区样式，如下所示：

  • 'quad_segs=#' ：用于近似四分之一圆的线段数（默认为 8）。

  • 'endcap=round|flat|square' ：endcap 样式（默认为“round”）。 “butt”被认为是“flat”的同义词。

  • 'join=round|mitre|bevel' ：连接样式（默认为“round”）。 “mitre”被认为是“mitre”的同义词。

  • 'mitre_limit=#.#' ：斜接比率限制（仅影响斜接连接样式）。 “miter_limit”被接受为“mitre_limit”的同义词。

  • 'side=both|left|right' :默认是 both。left 或 right 会对 geometry 做单侧缓冲，缓冲方向以线的走向为参照。此选项仅适用于 LINESTRING，对 POINT 或 POLYGON 无效。当指定 left 或 right 时，线段末端默认使用方形端帽。

[注意]

对于地理数据，这是对几何数据实现的一个轻量级封装。 它确定最适合地理对象边界框的平面空间参考系统（尝试 UTM、兰伯特方位角等积 (LAEA) 北/南极，最后是墨卡托）。 缓冲区在平面空间中计算，然后转换回 WGS84。 如果输入对象远大于 UTM 区域或跨越日期变更线，这可能不会产生所需的行为

[注意]

缓冲区操作可处理无效输入，并始终生成有效的多边形几何对象。以距离 0 进行缓冲常被用作修复无效多边形的一种方法。但对于此类修复操作，ST_MakeValid 更为适合，因为它能处理多面体MultiPolygon类型。

[注意]

缓冲有时用于执行近距离搜索。 对于此用例，使用ST_DWithin效率更高。
[注意]

此函数忽略 Z 维度。 即使在 3D 几何体上使用时，它也始终给出 2D 结果。

增强：2.5.0 - ST_Buffer的几何感知版本已得到增强，允许您指定要缓冲的一侧。side=both|left|right。

可用性：1.5 - ST_Buffer 已得到增强，以适应各种端接和接缝。 例如，您可能希望将道路线串转换为街道面，并希望将端点视为平面或正方形而不是圆。 添加了地理的薄包装器。

这个函数是由 GEOS 模块执行的。

此方法实现了 SQL 1.1 的 OGC 简单功能规范。 s2.1.1.3

该方法实现了SQL/MM规范。 SQL-MM IEC 13249-3: 5.1.30

示例

The textual results are rounded to whole coordinate units for readability. Each result remains available as text, while the manual initially favors the shared input/output figure.

quad_segs=8 (默认)

Code
SELECT ST_Buffer(
  ST_GeomFromText('POINT(100 90)'),
  50, 'quad_segs=8');
栅格输出
POLYGON((150 90,149 80,146 71,142 62,135 55,128 48,119 44,110 41,100 40,90 41,81 44,72 48,65 55,58 62,54 71,51 80,50 90,51 100,54 109,58 118,65 125,72 132,81 136,90 139,100 140,110 139,119 136,128 132,135 125,142 118,146 109,149 100,150 90))
Figure
Geometry figure for st-buffer-example-01

quad_segs=2

Code
SELECT ST_Buffer(
  ST_GeomFromText('POINT(100 90)'),
  50, 'quad_segs=2');
栅格输出
POLYGON((150 90,135 55,100 40,65 55,50 90,65 125,100 140,135 125,150 90))
Figure
Geometry figure for st-buffer-example-02

endcap=round join=round (默认)

Code
SELECT ST_Buffer(
  ST_GeomFromText('LINESTRING(50 50,150 150,150 50)'),
  10, 'endcap=round join=round');
栅格输出
POLYGON((143 157,144 158,146 159,148 160,150 160,152 160,154 159,156 158,157 157,158 156,159 154,160 152,160 150,160 50,160 48,159 46,158 44,157 43,156 42,154 41,152 40,150 40,148 40,146 41,144 42,143 43,142 44,141 46,140 48,140 50,140 126,57 43,56 42,54 41,52 40,50 40,48 40,46 41,44 42,43 43,42 44,41 46,40 48,40 50,40 52,41 54,42 56,43 57,143 157))
Figure
Geometry figure for st-buffer-example-03

endcap=square

Code
SELECT ST_Buffer(
  ST_GeomFromText('LINESTRING(50 50,150 150,150 50)'),
  10, 'endcap=square join=round');
栅格输出
POLYGON((143 157,144 158,146 159,148 160,150 160,152 160,154 159,156 158,157 157,158 156,159 154,160 152,160 150,160 50,160 40,140 40,140 126,57 43,50 36,36 50,143 157))
Figure
Geometry figure for st-buffer-example-04

endcap=flat

Code
SELECT ST_Buffer(
  ST_GeomFromText('LINESTRING(50 50,150 150,150 50)'),
  10, 'endcap=flat join=round');
栅格输出
POLYGON((143 157,144 158,146 159,148 160,150 160,152 160,154 159,156 158,157 157,158 156,159 154,160 152,160 150,160 50,140 50,140 126,57 43,43 57,143 157))
Figure
Geometry figure for st-buffer-example-05

join=bevel

Code
SELECT ST_Buffer(
  ST_GeomFromText('LINESTRING(50 50,150 150,150 50)'),
  10, 'join=bevel');
栅格输出
POLYGON((143 157,160 150,160 50,160 48,159 46,158 44,157 43,156 42,154 41,152 40,150 40,148 40,146 41,144 42,143 43,142 44,141 46,140 48,140 50,140 126,57 43,56 42,54 41,52 40,50 40,48 40,46 41,44 42,43 43,42 44,41 46,40 48,40 50,40 52,41 54,42 56,43 57,143 157))
Figure
Geometry figure for st-buffer-example-06

join=mitre mitre_limit=5.0 (默认最大斜接比率)

Code
SELECT ST_Buffer(
  ST_GeomFromText('LINESTRING(50 50,150 150,150 50)'),
  10, 'join=mitre mitre_limit=5.0');
栅格输出
POLYGON((160 174,160 50,160 48,159 46,158 44,157 43,156 42,154 41,152 40,150 40,148 40,146 41,144 42,143 43,142 44,141 46,140 48,140 50,140 126,57 43,56 42,54 41,52 40,50 40,48 40,46 41,44 42,43 43,42 44,41 46,40 48,40 50,40 52,41 54,42 56,43 57,160 174))
Figure
Geometry figure for st-buffer-example-07

join=mitre mitre_limit=1

Code
SELECT ST_Buffer(
  ST_GeomFromText('LINESTRING(50 50,150 150,150 50)'),
  10, 'join=mitre mitre_limit=1.0');
栅格输出
POLYGON((148 162,160 157,160 50,160 48,159 46,158 44,157 43,156 42,154 41,152 40,150 40,148 40,146 41,144 42,143 43,142 44,141 46,140 48,140 50,140 126,57 43,56 42,54 41,52 40,50 40,48 40,46 41,44 42,43 43,42 44,41 46,40 48,40 50,40 52,41 54,42 56,43 57,148 162))
Figure
Geometry figure for st-buffer-example-08

side=left

Code
SELECT ST_Buffer(
  ST_GeomFromText('LINESTRING(50 50,150 150,150 50)'),
  10, 'side=left');
栅格输出
POLYGON((150 50,150 150,50 50,43 57,143 157,144 158,146 159,148 160,150 160,152 160,154 159,156 158,157 157,158 156,159 154,160 152,160 150,160 50,150 50))
Figure
Geometry figure for st-buffer-example-09

side=right

Code
SELECT ST_Buffer(
  ST_GeomFromText('LINESTRING(50 50,150 150,150 50)'),
  10, 'side=right');
栅格输出
POLYGON((50 50,150 150,150 50,140 50,140 126,57 43,50 50))
Figure
Geometry figure for st-buffer-example-10

side=left join=mitre

Code
SELECT ST_Buffer(
  ST_GeomFromText('LINESTRING(50 50,150 150,150 50)'),
  10, 'side=left join=mitre');
栅格输出
POLYGON((150 50,150 150,50 50,43 57,160 174,160 50,150 50))
Figure
Geometry figure for st-buffer-example-11

right-hand winding, polygon boundary side=left

Code
SELECT ST_Buffer(
  ST_ForceRHR(ST_Boundary(ST_GeomFromText(
    'POLYGON ((50 50,50 150,150 150,150 50,50 50))'))),
  20, 'side=left');
栅格输出
POLYGON((50 50,50 150,150 150,150 50,50 50))
Figure
Geometry figure for st-buffer-example-12

right-hand winding, polygon boundary side=right

Code
SELECT ST_Buffer(
  ST_ForceRHR(ST_Boundary(ST_GeomFromText(
    'POLYGON ((50 50,50 150,150 150,150 50,50 50))'))),
  20, 'side=right');
栅格输出
POLYGON((50 50,50 70,50 150,150 150,150 50,70 50,50 50),(70 70,130 70,130 130,70 130,70 70))
Figure
Geometry figure for st-buffer-example-13
  

A buffered point approximates a circle. A buffered point forcing approximation of (see diagram) 2 points per quarter circle is poly with 8 sides (see diagram)

Code
SELECT ST_NPoints(ST_Buffer('POINT(100 90)'::geometry, 50)) As promisingcircle_pcount,
ST_NPoints(ST_Buffer('POINT(100 90)'::geometry, 50, 2)) As lamecircle_pcount;
栅格输出
promisingcircle_pcount | lamecircle_pcount
------------------------+-------------------
             33 |                9

A lighter, less smooth circle using only 2 points per quarter circle is an octagon.

The following example creates a 100 meter octagon in NAD83 longitude/latitude by transforming to the Massachusetts state plane meter projection and then buffering. The figure shows the input and output in separate panels because the coordinates are in different SRIDs.

Code
WITH input AS (
  SELECT ST_SetSRID(ST_Point(-71.063526, 42.35785), 4269) AS point_4269
), projected AS (
  SELECT point_4269,
         ST_Transform(point_4269, 26986) AS point_26986
  FROM input
)
SELECT point_4269 AS input_point_4269,
       ST_Buffer(point_26986, 100, 2) AS octagon_26986
FROM projected;
栅格输出
SRID=4269;POINT(-71.063526 42.35785) | SRID=26986;POLYGON((236057.5905746494 900908.7599186979,236028.30125276805 900838.0492405792,235957.5905746494 900808.7599186979,235886.87989653074 900838.0492405792,235857.5905746494 900908.7599186979,235886.87989653074 900979.4705968165,235957.5905746494 901008.7599186979,236028.30125276805 900979.4705968165,236057.5905746494 900908.7599186979))
Figure
Geometry figure for visual-st-buffer-15

Buffering a polygon by a positive distance and then by the same negative distance is a morphological closing operation. It can be useful for smoothing noisy boundaries, such as simplifying a coastline by removing narrow inlets and bays. The result intentionally changes the shape and area of the input, and the distance must be chosen in the units of the input SRS. For data in a geographic SRS, transform to a projected SRS suited to the operation first; for cartographic visualization in Web Mercator, using that display SRS can be appropriate.

Smooth a coastline using a 1 km closing operation, then simplify the result. The example uses Massachusetts State Plane meter units for the operation.

Code
WITH projected AS (
  SELECT id, ST_Transform(geom, 26986) AS geom
  FROM coast
),
closed AS (
  SELECT id, ST_Buffer(ST_Buffer(geom, 1000), -1000) AS geom
  FROM projected
)
SELECT id, ST_Transform(ST_SimplifyPreserveTopology(geom, 50), 4326) AS geom
FROM closed;

The same technique is described in Paul Ramsey's Removing Complexities. The final simplification step is optional; use ST_SimplifyPreserveTopology when polygonal validity matters, and check the result against the cartographic or analytical tolerance required by the application.

A small negative buffer can also be used as a heuristic to find narrow polygon spikes. The query below compares how much area and perimeter remain after erosion. A large erosion_index indicates that the perimeter dropped proportionally more than the area. This is only a preselection aid; the threshold and buffer distance must be chosen for the data units and the kind of spike being checked.

Code
WITH sample(id, geom) AS (
  VALUES
    ('plain', 'POLYGON((0 0,10 0,10 10,0 10,0 0))'::geometry),
    ('spike', 'POLYGON((0 0,10 0,10 10,5.2 10,5 16,4.8 10,0 10,0 0))'::geometry)
),
eroded AS (
  SELECT id, geom, ST_Buffer(geom, -0.5) AS eroded_geom
  FROM sample
),
scored AS (
  SELECT id,
         round((
           ST_Area(eroded_geom) / ST_Area(geom) /
           NULLIF(ST_Perimeter(eroded_geom) / ST_Perimeter(geom), 0)
         )::numeric, 3) AS erosion_index
  FROM eroded
  WHERE NOT ST_IsEmpty(eroded_geom)
)
SELECT id, erosion_index, erosion_index > 1.1 AS possible_spike
FROM scored
ORDER BY id;
栅格输出
id   | erosion_index | possible_spike
-------+---------------+----------------
 plain |         0.900 | f
 spike |         1.147 | t
Figure
Geometry figure for visual-st-buffer-16

A variable-distance buffer can be approximated by buffering each vertex of a line by a distance interpolated along the line, building the convex hull for each consecutive pair of vertex buffers, and unioning the segment hulls. As with any geometry buffer, distances are in the units of the input SRS.

Taper a line buffer from 5 to 25 units along the line.

Code
WITH line AS (
  SELECT 'LINESTRING(0 0, 100 0, 160 40)'::geometry AS geom
),
vertices AS (
  SELECT (dump).path[1] AS n,
         (dump).geom AS geom,
         line.geom AS line_geom
  FROM line
  CROSS JOIN LATERAL ST_DumpPoints(line.geom) AS dump
),
radii AS (
  SELECT n,
         geom,
         5 + (25 - 5) * ST_LineLocatePoint(line_geom, geom) AS radius
  FROM vertices
),
segments AS (
  SELECT n,
         geom,
         radius,
         lead(geom) OVER (ORDER BY n) AS next_geom,
         lead(radius) OVER (ORDER BY n) AS next_radius
  FROM radii
)
SELECT ST_Union(
         ST_ConvexHull(
           ST_Collect(
             ST_Buffer(geom, radius),
             ST_Buffer(next_geom, next_radius)
           )
         )
       ) AS tapered_buffer
FROM segments
WHERE next_geom IS NOT NULL;
栅格输出
POLYGON((96.758 -16.301,-0.975 -4.904,-1.913 -4.619,-2.778 -4.157,-3.536 -3.536,-4.157 -2.778,-4.619 -1.913,-4.904 -0.975,-5 0,-4.904 0.975,-4.619 1.913,-4.157 2.778,-3.536 3.536,-2.778 4.157,-1.913 4.619,-0.975 4.904,93.101 15.875,142.322 57.678,146.111 60.787,150.433 63.097,155.123 64.52,160 65,164.877 64.52,169.567 63.097,173.889 60.787,177.678 57.678,180.787 53.889,183.097 49.567,184.52 44.877,185 40,184.52 35.123,183.097 30.433,180.787 26.111,177.678 22.322,173.889 19.213,169.567 16.903,106.36 -15.355,103.242 -16.301,100 -16.62,96.758 -16.301))
Figure
Geometry figure for visual-st-buffer-17