[postgis-users] Checking the point location against a line

[Pedro Doria Meunier]

Hey G. Lu,

 

This is best accomplished programmatically (at least from where I stand :])

 

LatLon is your friend here
. (coords are returned as (+-)99.999999)

 

To determine if the point is above the line I’ve already shown you


 

About up, down, left, right
.

 

You can extract a single point from the line with pointn(geometry,1) 

(points start at 1 in line segs)

(should you want to debug—visually confirm cords—use :
astext(pointn(geometry,1))

 

The flux for it is loosely this:

 

If (pointLon> Linepoint[1].Lon) then RIGHT;

Elseif (pointLon<Linepoint[1]Lon) then LEFT;

Elseif (pointLat>Linepoint[1].Lat) then UP;

Elseif (pointLat<Linepoint[1].Lat) then DOWN;

Else FREAKISH_CASE!:]

 

<Gurus>

There’s probably a more elegant way to do this in PL/SQL


</Gurus>

 

 

HTH,

Pedro.

 

From: ray at codemeit.com [mailto:ray at codemeit.com] On Behalf Of Ray G. Lu
Sent: sábado, 7 de Abril de 2007 3:05
To: Pedro Doria Meunier; postgis-users at postgis.refractions.net
Subject: Re: [postgis-users] Checking the point location against a line

 

Hello Pedro ,

 

Thanks for your reply,

 

What I meant was how to determine P(x0,y0) 

is above the line or LEFT side of the line, 

or P(x2,y2) is below the line or RIGHT side of the line.

 

 

################################################

                                          P(x0,y0)  Above the line 
               
This is line
-------------------------------o------------------------------------- 
                                P(x1,y1) On the line

                                       P(x2,y2) Below the line 
################################################

 

Thanks,

 

G. LU
 

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