描述

返回栅格的凸包几何，包括 NoDataBandValue 波段像素。对于规则形状且未倾斜的栅格，这与 ST_Envelope 给出的结果或多或少相同，因此仅对不规则形状或倾斜的栅格有用。

	ST_Envelope 对坐标取整，因此在栅格周围添加了一个小缓冲区，所以答案与不取整的 ST_ConvexHull 略有不同。

示例

请参阅 PostGIS 栅格规范 以获取此图。

-- Note envelope and convexhull are more or less the same
SELECT ST_AsText(ST_ConvexHull(rast)) As convhull,
    ST_AsText(ST_Envelope(rast)) As env
FROM dummy_rast WHERE rid=1;

                        convhull                        |                env
--------------------------------------------------------+------------------------------------
 POLYGON((0.5 0.5,20.5 0.5,20.5 60.5,0.5 60.5,0.5 0.5)) | POLYGON((0 0,20 0,20 60,0 60,0 0))
                

-- now we skew the raster
-- note how the convex hull and envelope are now different
SELECT ST_AsText(ST_ConvexHull(rast)) As convhull,
    ST_AsText(ST_Envelope(rast)) As env
FROM (SELECT ST_SetRotation(rast, 0.1, 0.1) As rast
    FROM dummy_rast WHERE rid=1) As foo;

                        convhull                        |                env
--------------------------------------------------------+------------------------------------
 POLYGON((0.5 0.5,20.5 1.5,22.5 61.5,2.5 60.5,0.5 0.5)) | POLYGON((0 0,22 0,22 61,0 61,0 0))
                    

另请参见

ST_Envelope，ST_MinConvexHull，ST_ConvexHull，ST_AsText