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<p>Hi Darafei,</p>
<p>Thanks for the suggestion. <br>
</p>
<p>I must admit I have a bit of difficulty visualizing what this
exactly does, and had to look up that EPSG:4978 projection you
mention, but do I understand it right that the solution you
suggest should work for global data sets, and isn't influenced or
limited by the usual projection distortions?</p>
<p>I also understand this is not something I could easily run
myself, because this is experimental changes in underlying PostGIS
code? Or is there a set of PostGIS commands I need to run in
specific order to get such result, e.g. is it really as simple as
maybe:</p>
<p>"ST_ClusterDBSCAN(ST_Force3D(ST_Transform(<GEOMETRY_COLUMN>,4978)))"
??<br>
</p>
<p>Marco<br>
</p>
<div class="moz-cite-prefix">Op 21-12-2020 om 12:24 schreef Darafei
"Komяpa" Praliaskouski:<br>
</div>
<blockquote type="cite"
cite="mid:CAC8Q8tLRFvK5beM5PYKKya2=VwqVJhfa5jgr8K-pddNoUi1n3g@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="ltr">Hi,
<div><br>
</div>
<div>My last exercise in KMeans showed that it's enough to add
support for 3D distances instead of 2D distances in the code
and transform your geometry into EPSG:4978 (after Force3D).
That will cluster in a 3D XYZ coordinate system using straight
lines in 3D, which is usually good enough.</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Mon, Dec 21, 2020 at 2:15
PM Giuseppe Broccolo <<a
href="mailto:g.broccolo.7@gmail.com" moz-do-not-send="true">g.broccolo.7@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr">
<div dir="ltr">Hi Marco,<br>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">Il giorno dom 20 dic
2020 alle ore 10:03 Marco Boeringa <<a
href="mailto:marco@boeringa.demon.nl" target="_blank"
moz-do-not-send="true">marco@boeringa.demon.nl</a>>
ha scritto:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">Hi,<br>
<br>
Reading through the PostGIS documentation, I noticed the
<br>
"ST_ClusterDBSCAN" function takes a distance as one of
the inputs. Now <br>
the docs suggest the current algorithm only takes in
"geometry" type <br>
data. Is that true? Based on the distance input
variable, it would seem <br>
logical to have a "geography" variant as well, even if
that is a <br>
considerably slower variant considering the more complex
distance <br>
calculation.<br>
</blockquote>
<div><br>
</div>
<div>Yes, ST_ClusterDBSCAN takes just the geometry type in
input. This is because most of the algorithm</div>
<div>is implemented using utilities already existing in
GEOS for planar geometries.</div>
<div><br>
</div>
<div>Adding the support for the geography type would mean
to re-implement the algorithm specifically for</div>
<div>spherical objects, as you mentioned.</div>
<div><br>
</div>
<div>Regards,</div>
<div>Giuseppe.<br>
</div>
</div>
</div>
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<div><br>
</div>
-- <br>
<div dir="ltr" class="gmail_signature">
<div dir="ltr">Darafei "Komяpa" Praliaskouski<br>
OSM BY Team - <a href="http://openstreetmap.by/"
target="_blank" moz-do-not-send="true">http://openstreetmap.by/</a><br>
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