PostGIS之路——线性参考

1、ST_Line_Interpolate_Point

      返回一个点内插入一条线。第一个参数必须是 一个LINESTRING类型几何对象，第二个参数是一个float8类型，在0和1之间代表总长度一部分的，这个点将被定位。

geometryST_Line_Interpolate_Point(geometry a_linestring, float a_fraction);

可参考：http://hi.baidu.com/zhwtteng/item/9a6fcb3f79fe12cb1a96966c

示例SQL:

SELECT ST_AsEWKT(ST_Line_Interpolate_Point(the_line, 0.5))
FROM (SELECT ST_GeomFromEWKT('LINESTRING(1 2 3, 4 5 6, 6 7 8)') as the_line) As foo;

SELECT ST_AsText(ST_Line_Interpolate_Point(foo.the_line, ST_Line_Locate_Point(foo.the_line, ST_GeomFromText('POINT(4 3)'))))
FROM (SELECT ST_GeomFromText('LINESTRING(1 2, 4 5, 6 7)') As the_line) As foo;

2、ST_Line_Locate_Point

      返回a_point离a_linestring在上最近的点位置（这个位置表示为一个0到1浮点数）。点具体的位置我们可以使用前面介绍的ST_Line_Interpolate_Point取出。

floatST_Line_Locate_Point(geometry a_linestring, geometry a_point);

示例SQL：

SELECT ST_AsText(house_loc) As as_text_house_loc,startstreet_num +
CAST( (endstreet_num - startstreet_num)*ST_Line_Locate_Point(street_line, house_loc) As integer) As street_num
FROM (SELECT ST_GeomFromText('LINESTRING(1 2, 3 4)') As street_line,ST_MakePoint(x*1.01,y*1.03) As house_loc, 10 As startstreet_num,
20 As endstreet_num FROM generate_series(1,3) x CROSS JOIN generate_series(2,4) As y)
As foo WHERE ST_DWithin(street_line, house_loc, 0.2);

3、ST_Line_Substring

       返回一个线对象，作为一个的子字符串输入开始和结束在二维总长度的分数。第二个和第三个参数是 0和1之间的浮点数。

geometryST_Line_Substring(geometry a_linestring, float startfraction, float endfraction);

示例SQL：

SELECT ST_AsText(ST_Line_SubString(ST_GeomFromText('LINESTRING(25 50, 100 125, 150 190)'), 0.333, 0.666));

4、ST_LocateAlong

     返回一个根据指定的测量值与元素相匹配的导出几何对象。不支持面元素。

geometryST_LocateAlong(geometry ageom_with_measure, float a_measure, float offset);

示例SQL：

SELECT ST_AsText(the_geom) FROM (SELECT ST_LocateAlong(
ST_GeomFromText('MULTILINESTRINGM((1 2 3, 3 4 2, 9 4 3),
(1 2 3, 5 4 5))'),3) As the_geom) As foo;

5、ST_LocateBetween (2.0.0版本叫 ST_Locate_Between_Measures)

       根据量测值获得几何对象.

geometryST_LocateBetween(geometry geomA, float measure_start, float measure_end, float offset);

示例SQL:

SELECT ST_AsText(the_geom)
FROM
(SELECT ST_LocateBetween(
ST_GeomFromText('MULTILINESTRING M ((1 2 3, 3 4 2, 9 4 3),
(1 2 3, 5 4 5))'),1.5, 3) As the_geom) As foo;

 6、ST_LocateBetweenElevations

        根据量测值返回一个几何对象集合，这个只支持3D, 4D LINESTRINGS and MULTILINESTRINGS。

 geometryST_LocateBetweenElevations(geometry geom_mline, float elevation_start, float elevation_end);

示例SQL：

--Geometry collections are difficult animals so dump them
--to make them more digestable
SELECT ST_AsEWKT((ST_Dump(the_geom)).geom)
FROM
(SELECT ST_LocateBetweenElevations(
ST_GeomFromEWKT('LINESTRING(1 2 6, 4 5 -1, 7 8 9)'),6,9)As the_geom) As foo

7、ST_InterpolatePoint

       返回几何点闭合提供的点的测量维度值。

floatST_InterpolatePoint(geometry line, geometry point);

示例SQL：

SELECT ST_InterpolatePoint('LINESTRING M (0 0 0, 10 0 20)', 'POINT(5 5)');

8、ST_AddMeasure

      返回一个导出几何对象在开始和结束点之间线性内插一些元素。如果几何没有测量尺寸,添加一个。如果几何形状有一个测量维度,它超出写入一个新值。只支持LINESTRINGS 和 MULTILINESTRINGS。

geometryST_AddMeasure(geometry geom_mline, float measure_start, float measure_end);

示例SQL：
SELECT ST_AsText(ST_AddMeasure(
ST_GeomFromEWKT('MULTILINESTRINGM((1 0 4, 2 0 4, 4 0 4),(1 0 4, 2 0 4, 4 0 4))'),10,70)) As ewelev;