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List:       postgis-devel
Subject:    Re: [postgis-devel] Is there a reason we don't have an ST_Intersection aggregate function
From:       Komяpa <me () komzpa ! net>
Date:       2014-09-02 11:59:45
Message-ID: CAC8Q8tKpk2-+C1Ppnoc8axwYNVWRqNxUSETUBraHzpvtT_7=Rg () mail ! gmail ! com
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There's another thing with ST_Intersection/ST_Difference: sometimes you
have to make ST_Difference(geom, (select ST_Union(..,) where ...)) while
second operand evaluates to NULL (you shouldn't crop geometry). Currently
that leads to ST_Difference pushing out NULL. for my use case, that's not
desired semantics - can it be changed?


2014-09-01 4:16 GMT+03:00 Paragon Corporation <lr@pcorp.us>:

> I wasn't sure if we just thought there wasn't much utility in it or if
> there
> was a technical obstacle.
>
> I would think that would be easier to build than the other aggregates since
> as you add more geometries it shrinks and the current aggregate state is
> always the result of the previous state plus new geometry (so no need for
> an
> accumulation function or a final state function) and if you ever end up
> with
> a  geometry collection, you short-circuit out.
>
> Thanks,
> Regina
>
>
> _______________________________________________
> postgis-devel mailing list
> postgis-devel@lists.osgeo.org
> http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-devel
>



-- 
Darafei "Komяpa" Praliaskouski
OSM BY Team - http://openstreetmap.by/
xmpp:me@komzpa.net mailto:me@komzpa.net

[Attachment #5 (text/html)]

<div dir="ltr">There&#39;s another thing with ST_Intersection/ST_Difference: \
sometimes you have to make ST_Difference(geom, (select ST_Union(..,) where ...)) \
while second operand evaluates to NULL (you shouldn&#39;t crop geometry). Currently \
that leads to ST_Difference pushing out NULL. for my use case, that&#39;s not desired \
semantics - can it be changed?<br>

</div><div class="gmail_extra"><br><br><div class="gmail_quote">2014-09-01 4:16 \
GMT+03:00 Paragon Corporation <span dir="ltr">&lt;<a href="mailto:lr@pcorp.us" \
target="_blank">lr@pcorp.us</a>&gt;</span>:<br><blockquote class="gmail_quote" \
style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">

I wasn&#39;t sure if we just thought there wasn&#39;t much utility in it or if \
there<br> was a technical obstacle.<br>
<br>
I would think that would be easier to build than the other aggregates since<br>
as you add more geometries it shrinks and the current aggregate state is<br>
always the result of the previous state plus new geometry (so no need for an<br>
accumulation function or a final state function) and if you ever end up with<br>
a   geometry collection, you short-circuit out.<br>
<br>
Thanks,<br>
Regina<br>
<br>
<br>
_______________________________________________<br>
postgis-devel mailing list<br>
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<a href="http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-devel" \
target="_blank">http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-devel</a><br> \
</blockquote></div><br><br clear="all"><br>-- <br>Darafei &quot;Komяpa&quot; \
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>



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