<html><body><div style="color:#000; background-color:#fff; font-family:times new roman, new york, times, serif;font-size:12pt"><div></div><div><span><br></span></div><br><div class="yui_3_7_2_150_1386664103448_60" style="font-family: times new roman, new york, times, serif; font-size: 12pt;"><div class="yui_3_7_2_150_1386664103448_64" style="font-family: times new roman, new york, times, serif; font-size: 12pt;">Hi,<br><br>I
have a dataset with start & end points that we are represtnting as
linestrings. Many records do not have endpoints - so we are takimg the
median bearling for comparable startpoints & creating an arbitrary
endpoint.<br><br>While it is easy to get a bearing for a known endpoint
with ST_Azimuth(), is there a simple way in Postgis to get the point at a
defined distance & bearing? I've perused the docs & nothing
jumped out as an obvious solution.</div></div><div><br></div><div><br></div><div style="color: rgb(0, 0, 0); font-size: 16px; font-family: times new roman,new york,times,serif; background-color: transparent; font-style: normal;">Thanks,</div><div style="color: rgb(0, 0, 0); font-size: 16px; font-family: times new roman,new york,times,serif; background-color: transparent; font-style: normal;"><br></div><div style="color: rgb(0, 0, 0); font-size: 16px; font-family: times new roman,new york,times,serif; background-color: transparent; font-style: normal;"> Brent Wood<br></div> <div style="font-family: times new roman, new york, times, serif; font-size: 12pt;"> <div style="font-family: times new roman, new york, times, serif; font-size: 12pt;"> <div dir="ltr"> <hr size="1"> <font face="Arial" size="2"> <b><span style="font-weight:bold;">From:</span></b> Simon Greener <simon@spatialdbadvisor.com><br> <b><span style="font-weight:
bold;">To:</span></b> PostGIS Users Discussion <postgis-users@lists.osgeo.org> <br> <b><span style="font-weight: bold;">Sent:</span></b> Thursday, April 11, 2013 6:57 PM<br> <b><span style="font-weight: bold;">Subject:</span></b> Re: [postgis-users] Finding closet intersect point along direction of line<br> </font> </div> <div class="y_msg_container"><br><div id="yiv2930287765">
<style type="text/css">#yiv2930287765 body {font-family:'Times New Roman';font-size:13px;}</style>
<div><div>Adrian,</div><div><br>That's excellent.</div><div><br></div><div>regards</div><div>Simon</div><div><br></div><div>On Thu, 11 Apr 2013 16:51:14 +1000, <adrian.kitchingman@dse.vic.gov.au> wrote:<br></div><br><blockquote style="margin:0 0 0.80ex;border-left:#0000FF 2px solid;padding-left:1ex;"><font face="sans-serif" size="2">Thanks for the code Simon. After a few
tweaks I got it working perfectly in PostGIS2.</font><br><br><font face="sans-serif" size="2">Here's the updated code.</font><br><br><font face="sans-serif" size="2">Adrian</font><br><br><font face="sans-serif" size="2">CREATE OR REPLACE FUNCTION ST_Extend(eje_
geometry, bound_ geometry)</font><br><font face="sans-serif" size="2">RETURNS geometry</font><br><font face="sans-serif" size="2">AS $$</font><br><font face="sans-serif" size="2">-- Use Case: I need to "extend"
a linestring in another one. The new linestring must be</font><br><font face="sans-serif" size="2">-- obtained such as their new extremes
are the intersection of it with a</font><br><font face="sans-serif" size="2">-- polygon that contains it. The original
linestring is composed of only a</font><br><font face="sans-serif" size="2">-- linear segment.</font><br><font face="sans-serif" size="2">-- version: alfa , by Julio A. Galindo,
April 17, 2007: juliogalindoq at gmail.com</font><br><font face="sans-serif" size="2">DECLARE</font><br><font face="sans-serif" size="2"> b_ geometry = st_boundary(bound_);</font><br><font face="sans-serif" size="2"> dist float;</font><br><font face="sans-serif" size="2"> max_dist float
= 0;</font><br><font face="sans-serif" size="2"> n_points int;</font><br><font face="sans-serif" size="2"> pto_1 geometry;</font><br><font face="sans-serif" size="2"> pto_2 geometry;</font><br><font face="sans-serif" size="2"> first_pto geometry;</font><br><font face="sans-serif" size="2"> last_pto geometry;</font><br><font face="sans-serif" size="2"> u_1 float;</font><br><font face="sans-serif" size="2"> u_2 float;</font><br><font face="sans-serif" size="2"> norm float;</font><br><font face="sans-serif" size="2"> result text = 'LINESTRING(';</font><br><font face="sans-serif" size="2">BEGIN</font><br><font face="sans-serif" size="2"> IF st_GeometryType(eje_)
NOT LIKE 'ST_LineString' OR</font><br><font face="sans-serif" size="2"> st_GeometryType(bound_)
NOT LIKE 'ST_Polygon' THEN</font><br><font face="sans-serif" size="2"> RETURN
NULL;</font><br><font face="sans-serif" size="2"> END IF;</font><br><font face="sans-serif" size="2"> -- First Search
how far is the boundary: (worst case)</font><br><font face="sans-serif" size="2"> pto_1 := st_StartPoint(eje_);</font><br><font face="sans-serif" size="2"> pto_2 := st_EndPoint(eje_);</font><br><font face="sans-serif" size="2"> FOR i IN 1..st_NumPoints(b_)-1
LOOP</font><br><font face="sans-serif" size="2"> dist
:= st_distance(st_PointN(b_,i),pto_1);</font><br><font face="sans-serif" size="2"> IF
dist > max_dist THEN max_dist := dist; --END IF;</font><br><font face="sans-serif" size="2">
max_dist := dist;</font><br><font face="sans-serif" size="2"> END
IF;</font><br><font face="sans-serif" size="2"> dist
:= st_distance(st_PointN(b_,i),pto_2);</font><br><font face="sans-serif" size="2"> IF
dist > max_dist THEN max_dist := dist; --END IF;</font><br><font face="sans-serif" size="2">
max_dist := dist;</font><br><font face="sans-serif" size="2"> END
IF;</font><br><font face="sans-serif" size="2"> END LOOP;</font><br><font face="sans-serif" size="2"> -- Now extent the
linestring:</font><br><font face="sans-serif" size="2"> pto_2 := st_PointN(eje_,2);</font><br><font face="sans-serif" size="2"> u_1 := st_X(pto_2)-st_X(pto_1);</font><br><font face="sans-serif" size="2"> u_2 := st_Y(pto_2)-st_Y(pto_1);</font><br><font face="sans-serif" size="2"> norm := sqrt(u_1^2
+ u_2^2);</font><br><font face="sans-serif" size="2"> first_pto := st_MakePoint(st_X(pto_1)-u_1/norm*dist,st_Y(pto_1)-u_2/norm*dist);</font><br><font face="sans-serif" size="2"> n_points := st_nPoints(eje_);</font><br><font face="sans-serif" size="2"> IF n_points >
2 THEN</font><br><font face="sans-serif" size="2"> pto_1
:= st_PointN(eje_,n_points-1);</font><br><font face="sans-serif" size="2"> pto_2
:= st_PointN(eje_,n_points);</font><br><font face="sans-serif" size="2"> u_1
:= st_X(pto_2)-st_X(pto_1);</font><br><font face="sans-serif" size="2"> u_2
:= st_Y(pto_2)-st_Y(pto_1);</font><br><font face="sans-serif" size="2"> norm
:= sqrt(u_1^2 + u_2^2);</font><br><font face="sans-serif" size="2"> END IF;</font><br><font face="sans-serif" size="2"> last_pto := st_MakePoint(st_X(pto_2)+u_1/norm*dist,st_Y(pto_2)+u_2/norm*dist);</font><br><font face="sans-serif" size="2"> result :=
result || st_X(first_pto) || ' ' || st_Y(first_pto) || ',';</font><br><font face="sans-serif" size="2"> FOR i IN 1..st_NumPoints(eje_)
LOOP</font><br><font face="sans-serif" size="2"> result
:= result || st_X(st_PointN(eje_,i)) || ' ' || st_Y(st_PointN(eje_,i))
|| ',';</font><br><font face="sans-serif" size="2"> END LOOP;</font><br><font face="sans-serif" size="2"> result := result
|| st_X(last_pto) || ' ' || st_Y(last_pto) || ')';</font><br><font face="sans-serif" size="2"> -- Find the final
Linestring:</font><br><font face="sans-serif" size="2"> b_ := st_intersection(st_GeomFromText(result,st_SRID(eje_)),bound_);</font><br><font face="sans-serif" size="2"> RETURN b_;</font><br><font face="sans-serif" size="2"> END $$</font><br><font face="sans-serif" size="2"> LANGUAGE plpgsql</font><br><font face="sans-serif" size="2"> STABLE</font><br><font face="sans-serif" size="2"> RETURNS NULL ON NULL INPUT;</font><br><font size="3"><br></font><font face="Verdana" size="1"><br></font><br>
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</blockquote><br><br><br><div id="yiv2930287765M2Signature"><div>-- </div><div>Holder of "2011 Oracle Spatial Excellence Award for Education and Research."<br>SpatialDB Advice and Design, Solutions Architecture and Programming,<br>Oracle Database 10g Administrator Certified Associate; Oracle Database 10g SQL Certified Professional<br>Oracle Spatial, SQL Server, PostGIS, MySQL, ArcSDE, Manifold GIS, FME, Radius Topology and Studio Specialist.<br>39 Cliff View Drive, Allens Rivulet, 7150, Tasmania, Australia.<br>Website: www.spatialdbadvisor.com<br> Email: simon@spatialdbadvisor.com<br> Voice: +61 362 396397<br>Mobile: +61 418 396391<br>Skype: sggreener<br>Longitude: 147.20515 (147° 12' 18" E)<br>Latitude: -43.01530 (43° 00' 55" S)<br>GeoHash: r22em9r98wg<br>NAC:W80CK 7SWP3</div></div></div></div><br>_______________________________________________<br>postgis-users mailing list<br><a ymailto="mailto:postgis-users@lists.osgeo.org"
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