<div dir="ltr">Hello,<div><br></div><div>you can apply ST_ForceRHR, break your polygons into segments and sum length of the ones that go from right to left, that is, where ST_X(ST_StartPoint(geom)) < ST_X(ST_StartPoint(geom)).</div><div><br></div><div>That's basically visibility problem, been there somewhere around <a href="https://github.com/Komzpa/Mapnik-Sheets/blob/master/3d-buildings/3dbuil.xml#L95">https://github.com/Komzpa/Mapnik-Sheets/blob/master/3d-buildings/3dbuil.xml#L95</a><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">2015-06-17 18:12 GMT+03:00 Paolo Crosato <span dir="ltr"><<a href="mailto:paolo.crosato@targaubiest.com" target="_blank">paolo.crosato@targaubiest.com</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi,<br>
<br>
I have a set of 2d polygons representing buildings. For each one, I have to find the lenght of the edges that look towards north.<br>
<br>
Here <a href="http://imgur.com/HgpO2yH" rel="noreferrer" target="_blank">http://imgur.com/HgpO2yH</a> there is a small picture with a test case, I have to compute the lenght of the red edges.<br>
<br>
Has anybody any suggestion on how to do this in postgis?<br>
<br>
Thanks for any input,<br>
<br>
Regards<span class="HOEnZb"><font color="#888888"><br>
<br>
-- <br>
Paolo Crosato<br>
Software engineer/Custom Solutions<br>
e-mail: <a href="mailto:paolo.crosato@targaubiest.com" target="_blank">paolo.crosato@targaubiest.com</a><br>
<br>
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</font></span></blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature">Darafei "Komяpa" Praliaskouski<br>OSM BY Team - <a href="http://openstreetmap.by/" target="_blank">http://openstreetmap.by/</a><br><a href="mailto:xmpp%3Ame@komzpa.net" target="_blank">xmpp:me@komzpa.net</a> mailto:<a href="mailto:me@komzpa.net" target="_blank">me@komzpa.net</a><br></div>
</div>