postgis矢量瓦片几个函数理解

1. 一个完整实例

with mvtgeom as(
    select
             st_asmvtgeom(
                   geom,
                   lsy_bboxxuz4490(218453,43497,18),
                   --st_tileenvelope(18,218453,43496),
                   4096,
                   256,
                   false
              ) as geom,
              id
       from
             yh_map_supplypipe
       where
              st_Intersects(
                    geom,
                    sy_bboxxuz4490(218453,43497,18),
               )
) 
select 
        st_asmvt(mvtgeom.*, 'layerName',4096,'geom') 
from mvtgeom; 

解析1：geometry ST_AsMVTGeom(geometry geom, box2d bounds, integer extent=4096, integer buffer=256, boolean clip_geom=true);

把空间数据按照瓦片坐标方式进行坐标重新编排，在lsy_bboxxuz4490(218453,43497,18)里面的都是 0-4096，超出的有负数有更大的数

解析2：ST_AsMVT聚合函数用于将基于MapBox VectorTile坐标空间的几何图形转换为MapBox VectorTile二进制矢量切片

解析3：两个图层压缩成一个瓦片图层

WITH yh_map_supplypipemvt AS (
    SELECT
        ST_AsMVTGeom (
            geom,
            lsy_bboxxyz4490 (218453, 43497, 18),
            --st_tileenvelope(18,218453, 43496),
            4096,
            256,
            FALSE
        ) AS geom,
        ID
    FROM
        yh_map_supplypipe
    WHERE
        ST_Intersects (
            geom,
            lsy_bboxxyz4490 (218453, 43497, 18)
        )
),
 yh_map_drainpipemvt AS (
    SELECT
        ST_AsMVTGeom (
            geom,
            lsy_bboxxyz4490 (218453, 43497, 18),
            --st_tileenvelope(18,218453, 43496),
            4096,
            256,
            FALSE
        ) AS geom,
        ID
    FROM
        yh_map_drainpipe
    WHERE
        ST_Intersects (
            geom,
            lsy_bboxxyz4490 (218453, 43497, 18)
        )
) SELECT
    (
        (
            SELECT
                ST_AsMVT (
                    yh_map_supplypipemvt.*, 'yh_map_supplypipemvt',
                    4096,
                    'geom'
                ) AS mvt
            FROM
                yh_map_supplypipemvt
        ) || (
            SELECT
                ST_AsMVT (
                    yh_map_supplypipemvt.*, 'yh_map_supplypipemvt',
                    4096,
                    'geom'
                ) AS mvt
            FROM
                yh_map_supplypipemvt
        )
    ) AS mvt