[postgis-users] Need some help

[Zamil Murji]

What if the line is not a straight line but a diagonal one, then the Y will not be the same. 
Your example will work for lines like so: | but doesn't work for lines like so: / or \
For such lines, i do need an angle.

Thanks
Zamil

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net]On Behalf Of strk
Sent: Thursday, August 05, 2004 11:46 AM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] Need some help


On Thu, Aug 05, 2004 at 11:38:52AM -0600, Zamil Murji wrote:
> That's where I'm stuck, I have no clue on how to build that line. I know how to get the X/Y values from the line, but thats where I get lost.
> 
> Even some pseudo code would be nice...I know I have to use angles, but my knowledge is pretty limited in this domain. I should have paid more attention during some linear algebra classes.

To get a T you need no angle. Your line will have same Y as your
upper point Y for both point and X-(length/2) X+(length/2) for the
X of left-right points, where lenght is the lenght of your line.

--strk;

> 
> Thanks
> Zamil
> 
> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net
> [mailto:postgis-users-bounces at postgis.refractions.net]On Behalf Of strk
> Sent: Thursday, August 05, 2004 11:15 AM
> To: PostGIS Users Discussion
> Subject: Re: [postgis-users] Need some help
> 
> 
> On Thu, Aug 05, 2004 at 11:09:44AM -0600, Zamil Murji wrote:
> > I'm open to using pl/pgsql...any sample code to do it with that?
> 
> If you give it a try and report your code, I'm open to review it.
> Basically you'll need to construct a WKT representation of the
> line you need... see postgis manual on how to extract X/Y values
> from your points.
> --strk;
> 
> > 
> > Thanks
> > Zamil
> > 
> > -----Original Message-----
> > From: postgis-users-bounces at postgis.refractions.net
> > [mailto:postgis-users-bounces at postgis.refractions.net]On Behalf Of strk
> > Sent: Thursday, August 05, 2004 11:01 AM
> > To: PostGIS Users Discussion
> > Subject: Re: [postgis-users] Need some help
> > 
> > 
> > On Thu, Aug 05, 2004 at 10:53:06AM -0600, Zamil Murji wrote:
> > > Hello list,
> > > 
> > > I have a column in a table defined as a LINESTRING, the lines display just fine using mapserver. Now I want to create a line that is perpendicular to that line, but I want to do it with SQL. I can get the end point of the line, but I'm at a loss of what to do next. My goal is to create a T with the line that is already stored in the db. What is the quickest way to do something like this.
> > > 
> > > Thanks in advance,
> > > Zamil
> > 
> > Postgis does not currently support creating geometries with SQL.
> > You need pl/pgsql for that. 
> > 
> > --strk;
> > 
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