問(wèn)題

書(shū)接上文點(diǎn)抽稀，在加載低層級(jí)瓦片時(shí)，發(fā)現(xiàn)瓦片體積增大，渲染壓力也比較大。

思路

在上文點(diǎn)抽稀的基礎(chǔ)上稍作改造，提取多邊形中心點(diǎn)如法炮制，抽稀的結(jié)果再和原多邊形匹配，返回抽稀后的多邊形即可

SQL

select 
  b.geom, 
  a.count, 
  b.name 
from 
  (
    select 
      --用于分組
      width_bucket(
        st_x(c.geom), 
        st_xmin(
          ST_TileEnvelope(Z, X, Y)
        ), 
        st_xmax(
          ST_TileEnvelope(Z, X, Y)
        ), 
        50
      ) as grid_x, 
      width_bucket(
        st_y(c.geom), 
        st_ymin(
          ST_TileEnvelope(Z, X, Y)
        ), 
        st_ymax(
          ST_TileEnvelope(Z, X, Y)
        ), 
        50
      ) as grid_y, 
      --集合&選點(diǎn)&統(tǒng)計(jì)
      ST_GeometryN(
        st_collect(c.geom), 
        1
      ) as geom, 
      count(c.geom) 
    from 
      (
        select 
          st_centroid(geom) as geom 
        from 
          buildings
      ) as c --中心點(diǎn)拿出來(lái)抽稀
    where 
      st_intersects(
        c.geom, 
        ST_TileEnvelope(Z, X, Y)
      ) 
    group by 
      grid_x, 
      grid_y
  ) a, 
  buildings b 
where 
  a.geom && st_centroid(b.geom); --重新匹配原有幾何

效果

bucket_width=500

bucket_width=100

bucket_width=50

bucket_width=20

后續(xù)

頁(yè)面加載效果待續(xù)