Hi Facundo,
In PostgreSQL, you can use database VIEWS to see tables with X and Y
coordinates. This view would be defined using the st_x and st_y functions.
CREATE OR REPLACE VIEW my_view AS
SELECT gid, identifier, st_x(geometry) AS x, st_y(geometry) AS y
FROM my_table;
Now you can view this table MS Access and other programs, and the st_x()
and st_y() functions are hidden to the end-user. (This table is
"read-only", but to make this table editable so you can modify the x,y
coordinates directly, a few more steps are required).
Using the GEOMETRY type to store point locations has endless
applications, such as being able to use spatial SQL queries (find all
the red dots in the green polygons), reprojection into different
coordinate systems, and you can visualize and edit the data in GIS
applications (uDig, QGIS, AutoCAD Map3D, etc.). It is a worthwhile
investment if your work relies on anything spatial.
-Mike
Facundo Ciccioli wrote:
Hi. Here at work we are thinking of using PostGIS to store points
indicating locations (in the future we'll need polygons as well). I
was wondering if there is a way to, once I get the Point object stored
in the database (with something like "SELECT my_point_field FROM
my_table;"), query the data returned to obtain the x and y
coordinates. I read the "Simple features" defined by OpenGIS, and if I
understood correctly, it should NOT be possible what I want to do. The
standard states that the Geometry object's attributes should only be
accessed via SQL (in my case it would go "SELECT st_x(my_point_field),
st_y(my_point_field) FROM my_table;"). But as I said: *if I understood
correctly* :P.
So, is there a way to do this? I guess that what I'm
looking for is a library or something with the functions that access
the internal format of the points as stored in the database, or the
specifications of such format so that we could write a library like
that.
Thanks in advance.
FaQ
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