[R] Visualization of a Convex Hull in R (Possibly with RGL)

Lorenzo Isella
Tue, 26 Jul 2016 10:26:47 -0000

Dear All,
I am not an expert about the calculation and visualization of convex
hulls, but I am trying to do something relatively simple.
Please consider the snippet at the end of the email.
The array pts  represents the position of (the centres of) a set of
spheres in 3D (whose radius is 0.5).
I found the geometry package which provides bindings to the qhull
(http://www.qhull.org/) library and allows me to calculate the convex
hull of pts and some interesting properties, like the area and the
volume of the convex hull.
That is all fine, but I would like to represent the results in 3D.
I would like to see a set of spheres with the given position in pts
and the radius R=0.5 and the convex hull going based on the
coordinates of pts.
Does anybody know how to achieve that?
Many thanks

Lorenzo



####################################################################


library(geometry)


pts <- structure(list(x = c(0.145138112090815, 0.880429452229448,
-1.66682740805663,
-0.955356943224252, 1.09396798448412, -2.63620653885452,
0.190270563436841,
2.77638842095489, -0.0914977922901252, -0.484087722062158,
0.674992784754569,
1.02571108118502, 2.78789154912298, -0.146882388586427,
-1.71507089246001,
-1.87886026272455, 6.61540228778138, 7.46818822627362,
4.80777628045963,
6.35487269602107, 4.70026626314108, 3.44366671298125,
2.92460648354883,
5.07053866161192, 7.2164343710271, 6.93292242981006, 7.84238243682145,
7.4321237311656, 9.59692827237335, 8.3454086671306, 6.574251622581,
6.93340304175759), y = c(-0.189309482569001, 1.67057595730283,
-0.995542605143325, 2.31599069771684, 1.79876139786291,
0.165886909346058,
2.70740725397259, 1.70535678189514, -0.819087329147786,
0.967935667739331,
-2.53860079551206, -1.60932884056828, -1.42050583991613,
-2.36883245674979,
0.191848867151458, -1.58255618338079, 1.98324724741419,
3.0095048680572,
1.97159273200079, 2.26459561200295, 0.4461804374566, 1.87939977307282,
1.98510457359889, -0.103495422088799, -1.32050185858493,
0.584580736435273,
-2.97562362406436, 0.106204178143333, -2.0843758994948,
-1.1492729389287,
-2.13797391772643, -4.45916649729404), z = c(-1.44428170702261,
-1.45742688370091, -1.70267889327056, -1.93637881287001,
-3.4452409532781,
-3.02436538816822, 0.114790290814684, -2.10208878117278,
2.07425243689128,
1.26652602551291, 1.39914827137784, -0.345006925422662,
0.596828021941431,
3.351773622867, 2.68408561840144, 3.97006405709929, 0.82767367646934,
-0.662142231346811, 1.68344957582882, 2.92819854377685,
0.386683699222387,
-0.220305098209874, 2.37510769001993, -1.51041233970289,
-0.707073219742548,
-1.24585080403725, -1.63914669343685, 0.683153891726357,
-1.26623658129696,
1.95073173465968, -2.94804638502708, -0.635785458903106)), .Names
c("x",
"y", "z"), class = "data.frame", row.names = c(NA,
-32L))

res<-convhulln(pts, options = "FA")