PostGIS 通过SQL语句实现空间分析【入门级】

　　PostGIS是对象关系型数据库系统PostgreSQL的一个扩展，PostGIS提供如下空间信息服务功能:空间对象、空间索引、空间操作函数和空间操作符。同时，PostGIS遵循OpenGIS的规范。

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刚开始学习了一些SQL语句，尝试实现要素图层的空间分析：

--读取要素的几何信息（按照WKT描述）
select ST_AsText(geom) from dzzg where bsm=2715;
select ST_AsText(geom) from ckyd where bsm=420;
--求出dzzg.bsm为2715的要素和cykd.bsm为420的要素的相交部分
select ST_Intersection(ST_GeomFromText(ST_astext(a.geom)),ST_GeomFromText(ST_astext(b.geom)))
FROM dzzg a INNER JOIN ckyd b on ST_Intersects(ST_GeomFromText(ST_astext(a.geom)),ST_GeomFromText(ST_astext(b.geom)))
where a.bsm=2715 and b.bsm=420
 
//ST_Intersection表示求交
 
//红色部分表示判断相交 on ST_Intersects

--success
--选出dzzg和ckyd两个图层的相交部分
--只选择前5个 不然需要很多时间
SELECT b.bsm As bbsm, p.bsm As pbsm,
        ST_Intersection(ST_GeomFromText(ST_AsText(b.geom)), ST_GeomFromText(ST_AsText(p.geom))) As intersect_bp
    FROM dzzg b INNER JOIN ckyd p ON ST_Intersects(ST_GeomFromText(ST_AsText(b.geom)),ST_GeomFromText(ST_AsText(p.geom)))
    --WHERE ST_Overlaps(ST_GeomFromText(ST_AsText(b.geom)),ST_GeomFromText(ST_AsText(p.geom)))
    LIMIT 5
--从dzzg层中选出满足以下条件的要素，并显示相交部分
--1、标识码大于2000 [感觉有部分的geom值有问题，所以限定一下搜索范围]
--2、与ckyd中标识码为420的面相交
select  a.bsm,
st_astext(st_intersection(st_geomfromtext(st_astext(a.geom)),st_geomfromtext(st_astext(b.geom)))) as intersection
from dzzg a inner join ckyd b ON ST_Intersects(ST_GeomFromText(ST_AsText(a.geom)),ST_GeomFromText(ST_AsText(b.geom)))
where b.bsm=420 and a.bsm>2000
--查询与已知面相交的图形
SELECT bsm FROM dzzg where
ST_Intersects(
ST_GeomFromText('POLYGON((102.463 24.873,102.465 24.872,102.463 24.872,102.463 24.873))'), ST_GeomFromText(ST_AsText(geom))) and bsm>2700
--创建表
create table test(id1 int4,id2 int4);
select addgeometrycolumn('public','test','shape',4610,'POLYGON',2); //添加几何字段，4610表示坐标系，2表示二维要素
SELECT b.bsm As bbsm, p.bsm As pbsm,
        ST_AsText(ST_Intersection(ST_GeomFromText(ST_AsText(b.geom)), ST_GeomFromText(ST_AsText(p.geom)))) As intersect_bp
    FROM dzzg b INNER JOIN ckyd p ON ST_Intersects(ST_GeomFromText(ST_AsText(b.geom)),ST_GeomFromText(ST_AsText(p.geom)))
    LIMIT 3
--插入记录
--函数st_geomfromtext 表示从“WKT描述”构建几何图形
 
insert into test(id1,id2,shape)

values(
    21,699,st_geomfromtext('POLYGON((102.481862440151 24.9381407958162,
    102.480064171822 24.9380431117968,102.480009386288 24.9381143096393,
    102.481862440151 24.9381407958162))',4610)
);--删除已知表
drop table ckyd 

初步学习，持续更新......

参考：http://blog.sina.com.cn/s/blog_722b6a020102v5m9.html

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