插入WKT后，PostGIS会自动转换吗?

问题描述

我对PostGIS还是很陌生，所以请多多包涵.

I'm quite new to PostGIS so bear with me.

假设我有一个定义如下的表:

Suppose I have a table defined as follows:

CREATE TABLE gtest (name varchar, geom geometry);

首先，要插入的内容是:

At first, to insert, I was doing something like:

INSERT INTO gtest
VALUES (
    'Polygon',
    ST_GeomFromText('POLYGON((0 0,1 0,1 1,0 1,0 0))',4326)
);

然后我发现仅通过执行以下操作仍可以工作:

I then discovered that it still works by only doing this:

INSERT INTO gtest
VALUES (
    'Polygon',
    'SRID=4326;POLYGON((0 0,1 0,1 1,0 1,0 0))'
);

当我执行查询时未将geom值转换回WKT时，它们均已正确编码.如果我将该列转换为EWKT，则同样，一切都将正确显示.

When I do a query without converting the geom values back into WKT, they are both encoded properly. Same if I convert the column to EWKT, everything displays properly.

幕后是否正在进行转换?如果我不调用ST_GeomFromText()进行插入，使用该列的所有其他功能是否可以正常工作?

Is there a conversion going on behind the scenes? And if I insert without calling ST_GeomFromText(), will all other functions using the column work fine?

谢谢

推荐答案

有几种自动转换为geometry类型的类型.

There are several automatic cast to and from the geometry type.

您可以在PostgreSQL中键入\dC，您将看到所有可用的演员表，包括:

You can type \dC in PostgreSQL and you will see all available casts, including:

                                     List of casts
     Source type         |         Target type         |      Function      |   Implicit?
-------------------------+-----------------------------+--------------------+---------------
text                     | geometry                    | geometry           | yes

doc 或此教程.

由于强制转换是隐式的，这意味着您无需指定即可使用它.请注意，您可以使用::geometry:

Since the cast in implicit, it means you don't have to specify it to use it. Note that you can "force" it using ::geometry:

select st_asText('SRID=4326;POLYGON((0 0,1 0,1 1,0 1,0 0))'::geometry);
           st_astext
--------------------------------
 POLYGON((0 0,1 0,1 1,0 1,0 0))
(1 row)

关于列的可用性，该列的类型为geometry，因此该列中的任何内容均为geometry，并且可由需要geometry的任何函数使用.数据如何到达那里(自动转换，转换，从其他几何图形中提取等)不再重要.

Regarding the column usability, the column is of type geometry so anything that is in this column is a geometry and can be used by any function requiring a geometry. How the data got there (automatic cast, conversion, extraction from another geometry etc) is not relevant anymore.

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