Question

我在Postgis中有很多行（在Geoserver中导入）。我需要为没有步长的固定长度（1km，100米）的每条线创建（在新表中）多边形（或缓冲区中计数点具有固定颜色的缓冲区）。如何创建查询Postgis或可能与Leaflet（Geojson来自geoserver）？

Answer 1

要剪切线条，您必须使用ST_LINE_Substring

SELECT id,ST_Line_Substring(line,
  CASE WHEN i=0 THEN 0 ELSE (i*100)/ST_Length(line) END,
  CASE WHEN (i+1)*100<ST_Length(line) THEN ((i+1)*100)/ST_Length(line) ELSE 1 END),50,'endcap=flat')
FROM line, 
  (SELECT generate_series(0,floor(ST_Length(line)/100)::int) as i FROM line) as q

如果你希望ST_Buffer在两端都是平坦的，那么将ST_DIFFERENCE变得容易，如果你想要原始线末端以外的其他东西，它会变得更加复杂。然后我们必须WITH line_frags AS ( SELECT l.id,i, ST_Line_Substring(l.line, CASE WHEN i=0 THEN 0 ELSE (i*100)/ST_Length(l.line) END, CASE WHEN (i+1)*100<ST_Length(l.line) THEN ((i+1)*100)/ST_Length(l.line) ELSE 1 END) as frag, CASE WHEN (i+1)*100>ST_Length(l.line) THEN true ELSE false END as the_end FROM line AS l JOIN (SELECT id,generate_series(0,floor(ST_Length(l.line)/100)::int) as i FROM line AS l) as q ON q.id=l.id) SELECT CASE WHEN f1.i=0 AND f2.i IS NULL THEN ST_Buffer(f1.frag,50,'endcap=round') WHEN f2.i IS NOT NULL THEN ST_DIFFERENCE(ST_Buffer(f1.frag,50,'endcap=round'),ST_BUFFER(f2.frag,50,'endcap=flat')) ELSE ST_Buffer(f1.frag,50,'endcap=flat') END as buf FROM line_frags AS f1 LEFT JOIN line_frags AS f2 ON f1.id=f2.id AND (f1.i=0 and f2.i=1 OR f1.the_end AND f2.i=f1.i-1);然后缓冲下一个/前一个元素的缓冲区，不要忘记只有一个片段的情况

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如何在Postgis查询或Leaflet（geojson）上沿固定长度的线创建多边形？

1 个答案: