<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:times new roman, new york, times, serif;font-size:12pt"><DIV>Regina,</DIV>
<DIV>Thanks for taking the time to look at my question, the answer is yes to both of your assumpions:</DIV>
<DIV>1. Segments are cut at junctions.</DIV>
<DIV>2. I am trying to find contiguous segments from the intersection, but not for every intersection in the dataset, just for the intersection resulting from the streets that I specify, I'll use python to capture a pair of street names and generate the query dynamically.</DIV>
<DIV> </DIV>
<DIV>Thanks again,</DIV>
<DIV> </DIV>
<DIV>Andrew<BR></DIV>
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<B><SPAN style="FONT-WEIGHT: bold">From:</SPAN></B> "Obe, Regina" <robe.dnd@cityofboston.gov><BR><B><SPAN style="FONT-WEIGHT: bold">To:</SPAN></B> PostGIS Users Discussion <postgis-users@postgis.refractions.net><BR><B><SPAN style="FONT-WEIGHT: bold">Sent:</SPAN></B> Monday, December 15, 2008 8:58:30 AM<BR><B><SPAN style="FONT-WEIGHT: bold">Subject:</SPAN></B> RE: [postgis-users] Crossing roads<BR></FONT><BR>
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<DIV dir=ltr align=left><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2>Andrew,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2>Not sure I understand your question. Are you saying your street segments are cut such that they only connect at junctions. Kind of like tiger tlids.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2>And given each intersection, you are trying to find continguous segments from the intersection?</FONT></SPAN></DIV>
<DIV><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2>e.g.</FONT></SPAN></DIV>
<DIV><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=459435013-15122008>----------- ------------- --------------- <FONT face=Arial color=#0000ff size=2>Intersection -------------------------- ------------------------------- -----------------</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2> t3 t2 t1 s3 s4 sn</FONT></SPAN></DIV>
<DIV><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2> |a1</FONT></SPAN></DIV>
<DIV><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2> |a2</FONT></SPAN></DIV>
<DIV><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2> |an</FONT></SPAN></DIV>
<DIV><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2>So you would keep on collecting segments as long as they are connected to the previous ones?</FONT></SPAN></DIV>
<DIV><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2>Thanks,</FONT></SPAN></DIV>
<DIV><SPAN class=459435013-15122008><FONT face=Arial color=#0000ff size=2>Regina</FONT></SPAN></DIV>
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<FONT face=Tahoma size=2><B>From:</B> postgis-users-bounces@postgis.refractions.net [mailto:postgis-users-bounces@postgis.refractions.net] <B>On Behalf Of </B>Andrew Ross<BR><B>Sent:</B> Saturday, December 13, 2008 11:05 AM<BR><B>To:</B> postgis-users@postgis.refractions.net<BR><B>Subject:</B> [postgis-users] Crossing roads<BR></FONT><BR></DIV>
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<P><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Hi Everybody,</SPAN></FONT></P>
<P><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">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.<BR></SPAN></FONT></P>
<P><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><BR></SPAN></FONT></P>
<P><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">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, </SPAN></FONT><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">(street segments A, street segments B, street segments C and street segments D</SPAN></FONT><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">, as shown at the bottom</SPAN></FONT><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">)</SPAN></FONT><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY:
Arial">. </SPAN></FONT></P>
<P><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Can anybody give me a high level idea of what functions / methods can be used to achieve this? </SPAN></FONT></P>
<P><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">I¢ve gotten as far as identifying the 4 segments actually connected to the intersection using the ST_Intersection function. </SPAN></FONT></P>
<P><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">How would I get all other segments connected to these 4? </SPAN></FONT></P>
<P><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">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.</SPAN></FONT></P>
<P><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Thanks in advance,</SPAN></FONT></P>
<P><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Andrew</SPAN></FONT></P>
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