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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Hi Rodrigo, <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>That worked perfectly. Now I’ve
tried to take it a step further and I’m stuck. The ultimate reason I’m
trying to get the intersection is to select a segment of road using
line_substring given three road names. For example, a user specifies Twp 480
from Rge 20 to Rge 30. I want to extract that segment of road as a geometry.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Once you showed me how to select the
intersection, it seemed like it should be easy to add that to a line_locate_point
query and save another step, but I’m stuck.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>This is the query I tried:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='margin-left:36.0pt'><i><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy;
font-style:italic'>SELECT line_locate_point(road_geom,IntersectionPoint) AS
start FROM (SELECT road1.geom FROM (SELECT * FROM roads WHERE name = 'Twp 480')
AS road1 JOIN (SELECT * FROM roads WHERE name = 'Rge 20') AS road2 ON
road1.geom && road2.geom AND Intersects(road1.geom,road2.geom)) AS
road_geom, (SELECT Centroid(Intersection(road1.geom,road2.geom)) FROM (SELECT *
FROM roads WHERE name = 'Twp 480') AS road1 JOIN (SELECT * FROM roads WHERE
name = 'Rge 20') AS road2 ON road1.geom && road2.geom AND Intersects(road1.geom,road2.geom))
AS IntersectionPoint;<o:p></o:p></span></font></i></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>The error message I get is:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='margin-left:36.0pt'><i><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy;
font-style:italic'>ERROR: function line_locate_point(record, record) does not
exist<o:p></o:p></span></font></i></p>
<p class=MsoNormal style='margin-left:36.0pt'><i><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy;
font-style:italic'>SQL state: 42883<o:p></o:p></span></font></i></p>
<p class=MsoNormal style='margin-left:36.0pt'><i><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy;
font-style:italic'>Hint: No function matches the given name and argument types.
You may need to add explicit type casts.<o:p></o:p></span></font></i></p>
<p class=MsoNormal style='margin-left:36.0pt'><i><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy;
font-style:italic'>Character: 8<o:p></o:p></span></font></i></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>I’m assuming the error is related to
how I am selected the road geometry for the line_locate_point function. If I
break it into three stages, and select the road geometry, and then select the
point using the sql you showed me, and then select the line_locate_point
function, it works fine.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>If I can get this working, I’m
hoping to go another step further and wind up with a sql statement something
like:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='margin-left:36.0pt'><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy'>SELECT
line_substring(road_geom, start_measure, end_measure) FROM ( … sql to
select road geometry …, sql to select line_locate_point for start point as
above, sql to select line_locate_point for end point as above).<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>My other question is, is this the best way
to go about this?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Thanks in advance,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Rob<o:p></o:p></span></font></p>
<div>
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face="Times New Roman"><span style='font-size:12.0pt'>
<hr size=2 width="100%" align=center tabindex=-1>
</span></font></div>
<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
postgis-users-bounces@postgis.refractions.net
[mailto:postgis-users-bounces@postgis.refractions.net] <b><span
style='font-weight:bold'>On Behalf Of </span></b>Rodrigo Martín LÓPEZ GREGORIO<br>
<b><span style='font-weight:bold'>Sent:</span></b> Wednesday, August 08, 2007
1:00 PM<br>
<b><span style='font-weight:bold'>To:</span></b> PostGIS Users Discussion<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [postgis-users] SQL
Help selecting intersections</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>Hi Rob.<br>
<br>
You can make something like this:<o:p></o:p></span></font></p>
<div style='margin-left:30.0pt'>
<p class=MsoNormal><i><font size=3 face="Times New Roman"><span
style='font-size:12.0pt;font-style:italic'>SELECT *,
Centroid(Intersection(road1.the_geom,road2.the_geom)) AS intersectionPoint FROM
<br>
(SELECT * FROM roads WHERE name LIKE 'Township Road 524') AS road1<br>
JOIN <br>
(SELECT * FROM roads WHERE name LIKE 'Range Road 20') AS road2<br>
ON</span></font></i> <i><span style='font-style:italic'><br>
road1.the_geom && road2.the_geom AND
Intersects(road1.the_geom,road2.the_geom)</span></i><o:p></o:p></p>
</div>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'><br>
Obviously you can select just the columns you want o get extra info like X and
Y coordinates of the intersectionPoint doing something like: <o:p></o:p></span></font></p>
<div style='margin-left:30.0pt'>
<p class=MsoNormal><i><font size=3 face="Times New Roman"><span
style='font-size:12.0pt;font-style:italic'>SELECT *,
X(Centroid(Intersection(road1.the_geom,road2.the_geom))) AS xcoord,
Y(Centroid(Intersection(road1.the_geom,road2.the_geom))) AS Ycoord FROM <br>
(SELECT * FROM roads WHERE name LIKE 'Township Road 524') AS road1<br>
JOIN <br>
(SELECT * FROM roads WHERE name LIKE 'Range Road 20') AS road2<br>
ON</span></font></i> <i><span style='font-style:italic'><br>
road1.the_geom && road2.the_geom AND
Intersects(road1.the_geom,road2.the_geom)</span></i><o:p></o:p></p>
</div>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'><br>
You can also modify the WHERE condition in the search of each individual road
like using ILIKE instead of LIKE to make the search case insensitive, use % in
the LIKE condition to search with just part of the road name, etc. <br>
<br>
(This is just a simple solution, you can get better results doing more complex
things like having a separated table with road names and road id, making the
search in this table and getting the ids of the matched roads and then, having
a index on your road table by road_id, accessing just the roads that have
matched the previous search, etc.) <br>
<br>
If you have any question, ask me again.<br>
<br>
Rodrigo.<o:p></o:p></span></font></p>
<div>
<p class=MsoNormal><span class=gmailquote><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>On 8/8/07, <b><span style='font-weight:bold'>Rob
McCulley</span></b> <<a href="mailto:RMcCulley@county24.com">RMcCulley@county24.com
</a>> wrote:</span></font></span><o:p></o:p></p>
<div link=blue vlink=purple>
<div>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>Hi
there, </span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> </span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>I'm
looking for a little help with some SQL. I've got a table of roads with
names. I need to be able to get the intersection of two roads given the
two names of the roads. The problem I have is, most of my roads have
multiple segments with the same name.</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> </span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>Currently
I'm doing this in essentially three steps. For example, lets say I'm
looking for the intersection of Township Road 524 and Range Road 20. I
just took a look at my database, and there are two segments for Twp Rd 524 and
there are 5 segments for Rge Rd 20. My current solution is:</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> </span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>Step
1: Select all segments of Twp Rd 524.</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>Step
2: Iterate through each segment of Twp Rd 524 and select any segment of Rge Rd
20 that intersects it. After I'm finished the iteration, I have two
geometries that intersect, one from Twp Rd 524 and one from Rge Rd 20.</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>Step
3: Select the intersection of the two geometries to get a point geometry.</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> </span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>This
seems like a bit of a brute force method of doing things. In the example
case, I end up making four separate queries to the database. In some
cases it could be quite a few more. I'm sure there is a more elegant
solution, but I can't quite get my head around how to do it. Is it
possible to get the intersection of the roads given the names in a single SQL
statement?</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> </span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>Thank
You,</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>Rob
McCulley</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>County
of <st1:place w:st="on"><st1:PlaceName w:st="on">Vermilion</st1:PlaceName> <st1:PlaceType
w:st="on">River</st1:PlaceType></st1:place></span></font><o:p></o:p></p>
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