Thomas Preuth wrote:

> -----------------------------------------------------------------------------------------------------------------

> Hello,

>

> I have two questions concerning postgis.

> The issue is:

>

> The column the_geom includes lines (multilinestring) as geometries, which

> define their position by two coordinates. A symbol should be placed at

> first coordinate. The base of the symbol should be perpendicular to the

> line. Therefore I need the tilt angle of the multilinestring.

> So my questions:

> 1.)How can I extract the first coordinate of the multilinestring with a

> sql statement?

> 2.)How can I get the tilt angle of the multilinestring (to the horizontal)

> with a sql statement?

1.

SELECT startpoint(geometryN(the_geom,1)) FROM <table>

2.

I'm not sure what you exactly you mean by "tilt angle", but you

can extract the (x,y) coordinates from a linestring like this:

x( pointN( geometryN( the_geom,1), 1))

y( pointN( geometryN( the_geom,1), 1))

x( pointN( geometryN( the_geom,1), 2))

y( pointN( geometryN( the_geom,1), 2))

Postgresql supports all the trigonometry functions, so it should be

easy to compute the "tilt angle".

dave