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База данных: MySQL


ST_Buffer(g, d[, strategy1[, strategy2[, strategy3]]])

Returns a geometry that represents all points whose distance from the
geometry value g is less than or equal to a distance of d.

If the geometry argument is empty, ST_Buffer() returns an empty

If the distance is 0, ST_Buffer() returns the geometry argument

mysql> SET @pt = ST_GeomFromText('POINT(0 0)');
mysql> SELECT ST_AsText(ST_Buffer(@pt, 0));
| ST_AsText(ST_Buffer(@pt, 0)) |
| POINT(0 0) |

ST_Buffer() supports negative distances for Polygon and MultiPolygon
values, and for geometry collections containing Polygon or MultiPolygon
values. The result may be an empty geometry.

ST_Buffer() permits up to three optional strategy arguments following
the distance argument. Strategies influence buffer computation. These
arguments are byte string values produced by the ST_Buffer_Strategy()
function, to be used for point, join, and end strategies:

o Point strategies apply to Point and MultiPoint geometries. If no
point strategy is specified, the default is
ST_Buffer_Strategy('point_circle', 32).

o Join strategies apply to LineString, MultiLineString, Polygon, and
MultiPolygon geometries. If no join strategy is specified, the
default is ST_Buffer_Strategy('join_round', 32).

o End strategies apply to LineString and MultiLineString geometries. If
no end strategy is specified, the default is
ST_Buffer_Strategy('end_round', 32).

Up to one strategy of each type may be specified, and they may be given
in any order.

ST_Buffer() handles its arguments as described in the introduction to
this section, with these exceptions:

o For a negative distance for Point, MultiPoint, LineString, and
MultiLineString values, and for geometry collections not containing
any Polygon or MultiPolygon values, an ER_WRONG_ARGUMENTS
.html#error_er_wrong_arguments) error occurs.

o If multiple strategies of a given type are specified, an
.html#error_er_wrong_arguments) error occurs.



mysql> SET @pt = ST_GeomFromText('POINT(0 0)');
mysql> SET @pt_strategy = ST_Buffer_Strategy('point_square');
mysql> SELECT ST_AsText(ST_Buffer(@pt, 2, @pt_strategy));
| ST_AsText(ST_Buffer(@pt, 2, @pt_strategy)) |
| POLYGON((-2 -2,2 -2,2 2,-2 2,-2 -2)) |

mysql> SET @ls = ST_GeomFromText('LINESTRING(0 0,0 5,5 5)');
mysql> SET @end_strategy = ST_Buffer_Strategy('end_flat');
mysql> SET @join_strategy = ST_Buffer_Strategy('join_round', 10);
mysql> SELECT ST_AsText(ST_Buffer(@ls, 5, @end_strategy, @join_strategy))
| ST_AsText(ST_Buffer(@ls, 5, @end_strategy, @join_strategy)) |
| POLYGON((5 5,5 10,0 10,-3.5355339059327373 8.535533905932738, |
| -5 5,-5 0,0 0,5 0,5 5)) |

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