[postgis-users] Crossing roads

[Andrew Ross]

Hi Everybody,
I hope I'm posting to the right location (I just subscribed to this list).  I have sent this question before but have not seen it listed anywhere yet.


In any case, I have a road network in which all of the street segments are snapped together.  I need to group all of the line segments of two streets that cross each other (street 1 and street 2 as shown below) into 4 groups of segments defined as all of those located on either side of the intersection, (street segments A, street segments B, street segments C and street segments D, as shown at the bottom).  
 
Can anybody give me a high level idea of what functions / methods can be used to achieve this?  
 
I’ve gotten as far as identifying the 4 segments actually connected to the intersection using the ST_Intersection function.  
 
How would I get all other segments connected to these 4?  
 
Do I have to write a recursive function using ST_Touches ?  I’d rather not if there is a more elegant way of doing this.
 
Thanks in advance,
Andrew
 
 
 
                                    1
                                    1
                                    1
                                    1
            222222222222 X 22222222222222
                                    1
                                    1
                                    1
                                    1
 
 
 
                                    A
                                    A
                                    A
                                    A
            BBBBBBBBBBXCCCCCCCCCCC
                                    D
                                    D
                                    D
                                    D
 
 

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