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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Several years ago, I wrote some Python code to roughly georeference air photos. As part of that, I needed to come up with the best approximation of the heading
of the airplane. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">What worked pretty well was to do a really simple line fitting based on the points. My samples were points from an airplane that was attempting to fly in a
straight line, with vertices generated by a camera taking pictures at regular intervals, so that helped.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I simply split the vertices of the line into three groups by dividing the total number of points by 3. I averaged the x and y values in each group and then
created a line from the average coord from group1 to the average coord from group3.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Street data will likely be more variable (curved), but you may want to explore something like this. Of course, you would likely want to calculate these label
angles using pre-processing to speed up rendering time.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">David.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext"> mapserver-users-bounces@lists.osgeo.org [mailto:mapserver-users-bounces@lists.osgeo.org]
<b>On Behalf Of </b>Jan Hartmann<br>
<b>Sent:</b> Tuesday, February 21, 2012 11:18 AM<br>
<b>To:</b> Fawcett, David (MPCA)<br>
<b>Cc:</b> mapserver-users@lists.osgeo.org<br>
<b>Subject:</b> Re: [mapserver-users] Aligning labels within a polygon<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Going a step further:<br>
<br>
st_longestline(st_collect(the_geom),st_collect(the_geom))<br>
<br>
gives the longest line segment that can be drawn within the cluster of street address points. Works for non-curved streets. I'm still looking for a more intelligent way to thin out a polygon to a (multi)line.<br>
<br>
Jan<br>
<br>
On 02/21/2012 05:27 PM, Fawcett, David (MPCA) wrote: <o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">If you are storing the data in PostGIS, you could possibly take advantage of ST_Azimuth().
<a href="http://www.postgis.org/docs/ST_Azimuth.html">http://www.postgis.org/docs/ST_Azimuth.html</a></span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">It takes two point objects as the args, but you could potentially use the start and end points of your linestring.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">David.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">
<a href="mailto:mapserver-users-bounces@lists.osgeo.org">mapserver-users-bounces@lists.osgeo.org</a> [<a href="mailto:mapserver-users-bounces@lists.osgeo.org">mailto:mapserver-users-bounces@lists.osgeo.org</a>]
<b>On Behalf Of </b>Jan Hartmann<br>
<b>Sent:</b> Tuesday, February 21, 2012 10:23 AM<br>
<b>To:</b> <a href="mailto:mapserver-users@lists.osgeo.org">mapserver-users@lists.osgeo.org</a><br>
<b>Subject:</b> [mapserver-users] Aligning labels within a polygon</span><o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">Hi,<br>
<br>
I'm inputting lots of street address points in PostGIS, and try to generate labels for the streets. The convex hull of the points of a street approximate the course of the street, and I would like to position the streetname in the middle of the convex hull
polygon, aligned to its dominant angle (the polygons are generally quite narrow). Is there a way of doing this with MapServer? Perhaps by thinning out the polygon to a line, for then I can use "angle follow".<br>
<br>
Jan <o:p></o:p></p>
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