ruby-on-rails - st_split 返回原始行

Question

我想用 postgis 分割线串。

我的功能:

  @distance_b_to_a = Track.find_by_sql(
  ["SELECT
    ST_Split(line, ST_Closestpoint(pta,line))  AS dst_line
    FROM (
      SELECT
        'SRID=4326;LINESTRING(1.391991 46.441430,1.506078 46.556788)'::geometry line,
        'SRID=4326;POINT(1.396636962890625 46.442352066959174)'::geometry pta,
    ) data"
  ])

还有我的节目:

  <p>Test : <%= @distance_b_to_a.first.dst_line %></p>

返回我原来的线串:

Test : GEOMETRYCOLLECTION (LINESTRING (1.391991 46.44143, 1.506078 46.556788))

怎么了？

Answer 1

ST_Split返回通过拆分几何图形产生的几何图形集合，所以恐怕这是预期的结果，因为您的 LineString 只有两个点。

考虑以下 LineString ...

LINESTRING(18.6435 42.5412,18.8440 42.5453,18.846 42.3994)

.. 并运行此查询，该查询使用上述 LineString 中的第二点应用 ST_Split:

WITH j AS (
SELECT 
    'SRID=4326;POINT(18.8440 42.5453)'::GEOMETRY AS pta,
    'SRID=4326;LINESTRING(18.6435 42.5412,18.8440 42.5453,18.846 42.3994)'::GEOMETRY AS line
)
SELECT 
  ST_AsText(
  ST_Split(line,
    ST_ClosestPoint(pta,line))) FROM j

...返回带有两个 LineStrings 的 GeometryCollection:

                                                st_astext                                                 
----------------------------------------------------------------------------------------------------------
 GEOMETRYCOLLECTION(LINESTRING(18.6435 42.5412,18.844 42.5453),LINESTRING(18.844 42.5453,18.846 42.3994))
(1 Zeile)