Insert data to a spatial database in postgis

Question

I have create a table which has 3 fields: id(integer), name(char) and surface(polygon). When i try to insert a new row in this table by executing:

INSERT INTO public."Area" ("ID", "Name", "Surface") VALUES(0, 'myArea', POLYGON((0 0, 1 0, 1 1, 0 1, 0 0)));

I get this error:

SQL Error [42601]: ERROR: syntax error at or near "0" Position: 84

I searched in the documentation of postgis etc but i didnt find out how to define this field (same for points and linestring).

I also tried something like this:

INSERT INTO public."Area" ("ID", "Name", "Surface") VALUES(1, 'myArea', ST_GeomFromText('POLYGON((8 4, 10.5 4, 10.5 1.5, 8 1.5, 8 4))'));

but the result was :

SQL Error [42804]: ERROR: column "Surface" is of type polygon but expression is of type geometry Hint: You will need to rewrite or cast the expression. Position: 76

Could you please help me to find out which is my mistake?

Thank you a lot for your time!

Answer 1

Try ST_PolygonFromText instead of ST_GeomFromText.

Or declare the column as generic GEOMETRY, rather than POLYGON type.

Answer 2

The error message tells the column is of type polygon , which is anative postgres type . What one can do with this type is very limited and if you are working with spatial data, using Postgis and its geometry type is indicated.

To create a column containing geometries of the type polygon, with the projection 4326 , you would do

CREATE TABLE test (my_poly geometry(polygon,4326));

You can then load data using ST_GeomFromText .

Since your column is of geometry type, there is an automatic cast from text to geometry , or you can force it. Unlike in your 1st query, note that the polygon definition must be enclosed between quotes.

insert into test values ('polygon((0 0, 0 1, 1 1, 1 0, 0 0))'::geometry)

At last, it is technically possible to create a Postgis geometry and to cast it to Postgres native polygon type ( SELECT ST_GeomFromText('POLYGON((0 0, 0 1, 1 1, 1 0, 0 0))')::polygon; ), but doing so brings very little benefit since you still won't have access to most of Postgis functions (compute distances, reproject, compute intersections etc)