<div dir="ltr">Thank you all for your help! Graeme and Nicholas were on the same track I think, and Micha - I knew this would likely be very simple (and already a tool) in PostGIS, but it's not my go-to approach, so I'm actually going to try this out bc it will solve my problem AND give me a bit more experience with postgreSQL and PostGIS. Additionally, I received a handy function for completing this task in R. So many ways to tackle the same problem, and I've very grateful that all of you took the time to respond. I have the concept down of what to do now, and that's really what I needed. You guys are the best!<div><br></div><div>Thank you again!</div><div>Tina</div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Sun, Jul 10, 2016 at 2:37 AM, Micha Silver <span dir="ltr"><<a href="mailto:micha@arava.co.il" target="_blank">micha@arava.co.il</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="direction:ltr" bgcolor="#FFFFFF" text="#000000">
<font size="+1"><font face="Arial">This can be achieved using the
PostGIS function ST_MinimumBoundingCircle(). If you can import
your subplots point layer into a PostGIS database, then
(assuming the points have an attribute "subplot_id", and
geometry column "the_geom") you could do something like:<br>
<br>
</font></font><font size="+1"><tt>SELECT s.subplot_id,
ST_MinimumBoundingCircle(ST_Collect(s.the</tt><tt>_geom)</tt><tt>)
as the_geom</tt><tt><br>
</tt><tt> FROM subplots AS s</tt><tt><br>
</tt><tt> GROUP BY s.subplot_id;</tt></font><font size="+1"><font face="Arial"><br>
<br>
(Based on the example from
<a href="http://postgis.net/docs/ST_MinimumBoundingCircle.html" target="_blank">http://postgis.net/docs/ST_MinimumBoundingCircle.html</a>)<br>
<br>
<br>
I would also point out that there's a concept "Standard
Deviational Ellipse" for encircling points by an ellipse at a
certain stdev distance from the "center of gravity" of the
points. If this is of interest, you can implement it in
GRASS-GIS with the </font></font><font size="+1"><tt>v.ellipse</tt></font><font size="+1"><font face="Arial"> addon. <br>
<br>
</font></font><div><div class="h5"><br>
<div>On 08/07/2016 16:49, Tina Cormier
wrote:<br>
</div>
</div></div><blockquote type="cite"><div><div class="h5">
<div dir="ltr">Hi all,
<div><br>
</div>
<div>Looking for help aggregating some field data subplots to
the plot level. In the attached screenshot, you can see
clusters of 4 points (4 subplots = 1 plot). I'd like to create
a circle around each cluster that is the smallest circle that
would encompass all 4 points. Sort of like a convex hull, but
a circle (convex hull, in this case, would give me a
triangle). Is there a tool or a series of steps to accomplish
this without doing it manually? In the attribute table, I have
a unique ID for each plot/cluster. So for each plot ID (in
this case, consisting of 4 subplots), I'd like to build a
circle around all of the subplots.</div>
<div><br>
</div>
<div>I should also mention that it's not always 4 points
(subplots), and they aren't always covering the same size area
on the ground.</div>
<div><br>
</div>
<div>I have QGIS 2.14.2 as well as one of the nightly builds
from a few weeks ago (can download the newest one if
necessary).</div>
<div><br>
</div>
<div>Thanks in advance for any ideas/insights! Google has not
helped me so much yet with this one!</div>
<div>Tina</div>
<div><br>
</div>
<div><br>
</div>
<div><img src="cid:part1.B783CD59.C8CC032B@arava.co.il" alt="Inline image 2" height="496" width="544"><br>
</div>
</div>
<br>
<fieldset></fieldset>
<br>
</div></div><pre>_______________________________________________
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</font></span></blockquote><span class="HOEnZb"><font color="#888888">
<br>
<pre cols="72">--
Micha Silver
Arava Drainage Authority
+972-523-665918</pre>
</font></span></div>
</blockquote></div><br></div>