surf.tri: Find surface triangles from tetrahedral mesh

Description

Find surface triangles from tetrahedral mesh typically obtained with delaunayn.

Usage

surf.tri(p, t)

Arguments

An n-by-3 matrix. The rows of p represent n points in dim-dimensional space.

Matrix with 4 columns, interpreted as output of delaunayn.

Value

An m-by-3 index matrix of which each row defines a triangle. The indices refer to the rows in p.

Details

surf.tri and convhulln serve a similar purpose in 3D, but surf.tri also works for non-convex meshes obtained e.g. with distmeshnd. It also does not produce currently unavoidable diagnostic output on the console as convhulln does at the Rterm console--i.e., surf.tri is silent.

Examples

Run this code

# NOT RUN {
# }
# NOT RUN {
# more extensive example of surf.tri

# url's of publically available data:
data1.url = "http://neuroimage.usc.edu/USCPhantom/mesh_data.bin"
data2.url = "http://neuroimage.usc.edu/USCPhantom/CT_PCS_trans.bin"

meshdata = R.matlab::readMat(url(data1.url))
elec = R.matlab::readMat(url(data2.url))$eeg.ct2pcs/1000
brain = meshdata$mesh.brain[,c(1,3,2)]
scalp = meshdata$mesh.scalp[,c(1,3,2)]
skull = meshdata$mesh.skull[,c(1,3,2)]
tbr = t(surf.tri(brain, delaunayn(brain)))
tsk = t(surf.tri(skull, delaunayn(skull)))
tsc = t(surf.tri(scalp, delaunayn(scalp)))
rgl::rgl.triangles(brain[tbr,1], brain[tbr,2], brain[tbr,3],col="gray")
rgl::rgl.triangles(skull[tsk,1], skull[tsk,2], skull[tsk,3],col="white", alpha=0.3)
rgl::rgl.triangles(scalp[tsc,1], scalp[tsc,2], scalp[tsc,3],col="#a53900", alpha=0.6)
rgl::rgl.viewpoint(-40,30,.4,zoom=.03)
lx = c(-.025,.025); ly = -c(.02,.02);
rgl::rgl.spheres(elec[,1],elec[,3],elec[,2],radius=.0025,col='gray')
rgl::rgl.spheres( lx, ly,.11,radius=.015,col="white")
rgl::rgl.spheres( lx, ly,.116,radius=.015*.7,col="brown")
rgl::rgl.spheres( lx, ly,.124,radius=.015*.25,col="black")
# }
# NOT RUN {
# }

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