[postgis-users] Absolute Beginner

[Obe, Regina]

Bob,

Unfortunately I'm not too familiar with Delphi (aside from its some
Pascal derivative) and I guess no one is in this group since no one
responded to your question.

I guess it depends what Delphi is expecting for the Canvas - e.g. can it
use SVG maybe or most unlikely (WKT  or WKB representations).  At
anyrate I suspect you are more likely to find Delphi plugins for
rendering SVG than any other format output by PostGIS.

If you can find SVG plugins, there is an asSVG function in PostGIS that
may prove useful to you.

As far as storing the path, you could put it in your database as a
LINESTRING of the form

INSERT INTO temppath(fieldname)
	VALUES(ST_GeomFromText('LINESTRING(1 2,3 12)'))

You can ignore use of SRID since you don't care about Geography.

Then query it as SVG format with

SELECT AsSVG(fieldname)
FROM temppath

or expand it out to x and y with something like

SELECT somekeyfield, ST_x(the_geom) as x, ST_y(the_geom) as y
FROM 
	(SELECT somekeyfield, ST_PointN(fieldname, generate_series(1,
ST_numpoints(fieldname)) As the_geom
		FROM temppath)  as foo

That will give you the x and y coordinates of each point of the line
string (with all belonging to the same linestring having
the same somekeyfield

and then you can just plot the x and y on canvas.

Hope that helps,
Regina








-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Bob
Pawley
Sent: Monday, April 21, 2008 1:25 PM
To: PostGIS Users Discussion
Subject: [postgis-users] Absolute Beginner

I know that most, if not all, on this list are interested in the
geography
side of GIS.

However, I have a question on the geometry side.

I have a Delphi Canvas that I need to connect to a PostgreSQL database.

What is the minimum table structure that is needed to hold the vector
coordinates such as this path ((1,2), (3, 12)) so that it will draw the
line
in Delphi?

Perhaps the Delphi knowledgeable people can let me know if the following
query is any where near correct to accomplish this action.

Thanks in advance.

Bob
     PSQLQuery1.Close;
      PSQLQuery1.SQL.Clear;
      PSQLQuery1.SQL.Add ('Select * fieldname ');
      PSQLQuery1.SQL.Add ('FROM temppath');
      PSQLQuery1.Prepare;
      PSQLQuery1.Open;
      PSQLQuery1.First ;
      i2:= PSQLQuery1.FieldByName('fieldname').AsInteger ;
      testfrm:= IntToStr(i2); 

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