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<TITLE>RE: postgis-users] a line' s direction</TITLE>
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<P><FONT SIZE=2 FACE="Arial">Ahmet,</FONT>
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<P><FONT SIZE=2 FACE="Arial">You would use a query like the following, which returns the azimuth from the start point to the end point of a simple line(string):</FONT></P>
<P><FONT SIZE=2 FACE="Arial">SELECT azimuth(pointn(the_geom, 1), </FONT>
<BR><FONT SIZE=2 FACE="Arial">pointn(the_geom, npoints(the_geom))) as azimuth</FONT>
<BR><FONT SIZE=2 FACE="Arial">FROM rivers;</FONT>
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<P><FONT SIZE=2 FACE="Arial">If you need to deal with multi geometries, it would get a bit more complicated. For example, the azimuth from the start point to the end point of the first geometry:</FONT></P>
<P><FONT SIZE=2 FACE="Arial">SELECT azimuth(pointn(geometryn(the_geom, 1), 1), </FONT>
<BR><FONT SIZE=2 FACE="Arial">pointn(geometryn(the_geom, 1), npoints(the_geom))) as azimuth</FONT>
<BR><FONT SIZE=2 FACE="Arial">FROM rivers;</FONT>
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<P><FONT SIZE=2 FACE="Arial">Cheers,</FONT>
<BR><FONT SIZE=2 FACE="Arial">Hartmut</FONT>
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<P><FONT SIZE=2 FACE="Arial">Hartmut Tschauner</FONT>
<BR><FONT SIZE=2 FACE="Arial">Department of Archaeology</FONT>
<BR><FONT SIZE=2 FACE="Arial">Seoul National University</FONT>
<BR><FONT SIZE=2 FACE="Arial">Gwanak-Gu Sillim 9-dong San 56-1</FONT>
<BR><FONT SIZE=2 FACE="Arial">Seoul, 151-742</FONT>
<BR><FONT SIZE=2 FACE="Arial">Korea</FONT>
<BR><FONT SIZE=2 FACE="Arial">ph. +82 (2) 880-9260</FONT>
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<P><FONT FACE="Times New Roman">>thank you for your help about line direction. I tested: bzk=> select astext(wkb_geometry) from bartin_fay limit 1; astext >----------------------------------------------------------- LINESTRING(458329.385 4604735.295,458326.082 4604735.287) (1 row) bzk=> select public.azimuth('point(458329.385 4604735.295)', 'point(458326.082 4604735.287)'); azimuth ------------------ 269.861227562345 (1 row) >~~~~~~~~~~~~~~~~~~ which function can I use to get end points of lines to input function ? I have a huge dataset containing linestring geometric data. kind regards </FONT></P>
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