I'll try starting from this.<div><br></div><div>Thank you very much<br><br><div class="gmail_quote">On Sat, Mar 10, 2012 at 3:51 PM, Stephen Woodbridge <span dir="ltr"><<a href="mailto:woodbri@swoodbridge.com">woodbri@swoodbridge.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="im">On 3/10/2012 2:20 AM, Aurélien FILEZ wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi,<br>
<br>
This table is build with lines I decompose in segments of 2 points.<br>
<br>
Maybe it is better to act from these full lines, searching points used<br>
by more than one line ?<br>
</blockquote>
<br></div>
Yes, but the question that I am trying to answer is How are you going to do the efficiently?<br>
<br>
I just noticed that you already have v1 and v2 assigned, so you can do something like this:<br>
<br>
create table vertices_tmp as<br>
select id, count(*) as cnt from<br>
(select v1 as id from edge union all select v2 as id from edge) as foo group by id;<br>
<br>
Now to find all the the nodes where cnt=2<br>
<br>
select id from vertices_tmp where cnt=2;<br>
<br>
And you write a stored procedure to merge the two edges.<br>
<br>
-Steve<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="im">
Thanks,<br>
Kin<br>
<br>
On Fri, Mar 9, 2012 at 5:48 PM, Stephen Woodbridge<br></div><div><div></div><div class="h5">
<<a href="mailto:woodbri@swoodbridge.com" target="_blank">woodbri@swoodbridge.com</a> <mailto:<a href="mailto:woodbri@swoodbridge.com" target="_blank">woodbri@swoodbridge.<u></u>com</a>>> wrote:<br>
<br>
On 3/9/2012 11:39 AM, Aurélien FILEZ wrote:<br>
<br>
Hi all,<br>
<br>
My edge table has some useless nodes. For example :<br>
<br>
edge_id v1 v2 the_geom<br>
1 1 2 LINESTRING(x1 y1, x2 y2)<br>
2 2 3 LINESTRING(x2 y2, x3 y3)<br>
<br>
But the vertex 2 is no used in any other edge.<br>
<br>
So I would like reduce my graph to transforme this previous<br>
example to :<br>
edge_id v1 v2 the_geom<br>
1 1 3 LINESTRING(x1 y1, x2 y2, x3 y3)<br>
<br>
Is there is a way to do that ?<br>
<br>
Thank you all :)<br>
<br>
<br>
There is no automatic way to do this. I have done a lot of graph<br>
analysis by adding a cnt column to the vertices_tmp column and then<br>
updating it to the count of edges connected to that vertex.<br>
<br>
Then you can do things like look for:<br>
<br>
deadends - cnt=1<br>
connected lines - cnt=2<br>
<br>
You could write a stored procedure to that the connected lines, join<br>
them together, and update the relevant tables to reflect the new<br>
topology.<br>
<br>
-Steve<br>
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