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:
SELECT s.subplot_id,
ST_MinimumBoundingCircle(ST_Collect(s.the_geom))
as the_geom
FROM subplots AS s
GROUP BY s.subplot_id;
(Based on the example from
http://postgis.net/docs/ST_MinimumBoundingCircle.html)
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 v.ellipse addon.
On 08/07/2016 16:49, Tina Cormier
wrote:
Hi all,
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.
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.
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).
Thanks in advance for any ideas/insights! Google has not
helped me so much yet with this one!
Tina
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--
Micha Silver
Arava Drainage Authority
+972-523-665918
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