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<div class="moz-cite-prefix">Thank you very much! I'll try with this
approach.<br>
<br>
Regards,<br>
<br>
Paolo<br>
<br>
Il 17/06/2015 18:24, Rémi Cura ha scritto:<br>
</div>
<blockquote
cite="mid:CAJvUf_uOJfLRnpuADdJz9Ukv9P19x=9QEJg8TqxL1W8DkZBknA@mail.gmail.com"
type="cite">
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<div class="gmail_default"
style="font-family:monospace,monospace">Hm,<br>
</div>
<div class="gmail_default"
style="font-family:monospace,monospace">quite easy normally
(method proposed above won't work).<br>
</div>
<div class="gmail_default"
style="font-family:monospace,monospace">First break your
polygon into segment, for instance with <br>
<a moz-do-not-send="true"
href="https://github.com/Remi-C/PPPP_utilities/blob/master/postgis/rc_DumpSegments.sql">https://github.com/Remi-C/PPPP_utilities/blob/master/postgis/rc_DumpSegments.sql</a><br>
</div>
<div class="gmail_default"
style="font-family:monospace,monospace">Then, for each
segment, compute the angle between first and last point, using
<code class=""><span class="">ST_Azimuth, and st_pointN.<br>
<br>
</span></code></div>
<div class="gmail_default"
style="font-family:monospace,monospace"><code class=""><span
class="">Now, keep the segment where the abs(angle) is
between pi/2<br>
-tolerancy and pi/2+tolerancy<br>
( you should add a tolerancy , nobody will be facing
exactly north)</span><b class="">.<br>
</b></code></div>
<div class="gmail_default"
style="font-family:monospace,monospace"><code class=""><b
class="">Now simply sum the st_length of found segments.<br>
<br>
</b></code></div>
<div class="gmail_default"
style="font-family:monospace,monospace"><code class=""><b
class="">Cheers,<br>
</b></code></div>
<div class="gmail_default"
style="font-family:monospace,monospace"><code class=""><b
class="">Rémi-C<br>
</b></code></div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">2015-06-17 17:40 GMT+02:00 Komяpa <span
dir="ltr"><<a moz-do-not-send="true"
href="mailto:me@komzpa.net" target="_blank">me@komzpa.net</a>></span>:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<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 moz-do-not-send="true"
href="https://github.com/Komzpa/Mapnik-Sheets/blob/master/3d-buildings/3dbuil.xml#L95"
target="_blank">https://github.com/Komzpa/Mapnik-Sheets/blob/master/3d-buildings/3dbuil.xml#L95</a><br>
</div>
</div>
<div class="gmail_extra">
<div>
<div class="h5"><br>
<div class="gmail_quote">2015-06-17 18:12 GMT+03:00
Paolo Crosato <span dir="ltr"><<a
moz-do-not-send="true"
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 moz-do-not-send="true"
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><font color="#888888"><br>
<br>
-- <br>
Paolo Crosato<br>
Software engineer/Custom Solutions<br>
e-mail: <a moz-do-not-send="true"
href="mailto:paolo.crosato@targaubiest.com"
target="_blank">paolo.crosato@targaubiest.com</a><br>
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<span class="HOEnZb"><font color="#888888">-- <br>
<div>Darafei "Komяpa" Praliaskouski<br>
OSM BY Team - <a moz-do-not-send="true"
href="http://openstreetmap.by/" target="_blank">http://openstreetmap.by/</a><br>
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href="mailto:xmpp%3Ame@komzpa.net" target="_blank">xmpp:me@komzpa.net</a>
mailto:<a moz-do-not-send="true"
href="mailto:me@komzpa.net" target="_blank">me@komzpa.net</a><br>
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<pre class="moz-signature" cols="72">--
Paolo Crosato
Software engineer/Custom Solutions
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