[postgis-users] Creating a linestring from two points

[Per-Olof Norén]

Hi Dave,
Sorry for the delay. I managed to figure somthing similar out before you 
could answer it.

Anyway, I used the function x(point1) instead of  xmin though. Isn´t a 
point´s bounding box the point itself?
or is a point´s bounding box  point+1 unit in every direction? Need 
update using your suggestion?

My query:
update lank set lank_geom = 
GeometryFromText('LINESTRING(' || x(parent.nod_geom) || ' ' || 
y(parent.nod_geom)
 || ',' || x(child.nod_geom) || ' ' || y(child.nod_geom) || ')', 30800)
from    lank l,
        nod parent,
        nod child
where   lank.parent_nod_id = parent.nod_id
        and lank.child_nod_id = child.nod_id
        and l.parent_nod_id = l.parent_nod_id


Thanx in advance,
Per-Olof


David Blasby wrote:

>Per-Olof,
>
>Unfortunately OGC didnt define any constructors for geometries.  I should
>really add a few functions to do this - perhaps I'll get some time in the
>next little while.
>
>If you want to construct a line from 2 points, I suggest you build up a WKT
>string:
>
>Lets look at a simple example - a table with 3 geometry columns called
>'point1','point2','line'.  The point1 and point2 column have points in them.
>
>The function xmin(geometry) returns the xmin of the geometry's bounding
>box.  For a point, the points X value is the same as the bounding box's X
>value.  The '||' operator concatenates 2 strings.
>
>UPDATE <table>  SET line =
>    geometryFromText(
>       'LINESTRING('|| xmin(point1)||' ' || ymin(point1) ||','||
>xmin(point2) || ' '||  ymin(point2) || ')'
>    );
>
>dave
>
>
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