# inst/rcode/createpolyeders.r In dti: Analysis of Diffusion Weighted Imaging (DWI) Data

```#
#  This code was used to create structures defining the polyeders/
#  triangulations used in 3D visualization
#
phi <- (1+sqrt(5))/2
icosa0 <- list(vertices=matrix(c(0,1,phi,
0,-1,phi,
0,1,-phi,
0,-1,-phi,
1,phi,0,
1,-phi,0,
-1,phi,0,
-1,-phi,0,
phi,0,1,
phi,0,-1,
-phi,0,1,
-phi,0,-1),3,12)/sqrt((5+sqrt(5))/2),
indices=c(1,2,9,
1,2,11,
1,5,7,
1,5,9,
1,7,11,
2,6,8,
2,6,9,
2,8,11,
3,4,10,
3,4,12,
3,5,7,
3,5,10,
3,7,12,
4,6,8,
4,6,10,
4,8,12,
5,9,10,
6,9,10,
7,11,12,
8,11,12),
edges=matrix(c(1,2,
1,5,
1,7,
1,9,
1,11,
2,6,
2,8,
2,9,
2,11,
3,4,
3,5,
3,7,
3,10,
3,12,
4,6,
4,8,
4,10,
4,12,
5,7,
5,9,
5,10,
6,8,
6,9,
6,10,
7,11,
7,12,
8,11,
8,12,
9,10,
11,12),2,30),
nv=12,
ni=20,
ne=30)
refine.polyeder <- function(polyeder){
norm <- function(x) sqrt(sum(x^2))
ni <- polyeder\$ni
nv <- polyeder\$nv
ne <- polyeder\$ne
vertices <- polyeder\$vertices
indices <- matrix(polyeder\$indices,3,ni)
edges <- polyeder\$edges
nnv <- nv+ne
nni <- 4*ni
nne <- nnv+nni-2# ne+ne+3*ni
nvertices <- matrix(0,3,nnv)
nindices <- array(0,c(3,4*ni))
nedges <- matrix(0,2,nne)
nvertices[,1:nv] <- vertices
vorigin <- matrix(0,2,ne)
for(i in 1:ne){
vert <- apply(vertices[,edges[,i]],1,mean)
e1 <- edges[,i]
v1 <- i+nv
nedges[,2*i-1] <- c(e1[1],i+nv)
nedges[,2*i] <- c(e1[2],i+nv)
vorigin[,i] <- e1
nvertices[,nv+i] <- vert/norm(vert)
}
ne2 <- 2*ne
ne22 <- ne2-2
ne21 <- ne2-1
for(i in 1:ni){
i4 <- 4*i
i3 <- 3*i
ind0 <- indices[,i]
e1 <- ind0[1:2]
e2 <- ind0[c(1,3)]
e3 <- ind0[2:3]
v1 <- (1:ne)[apply((vorigin-e1)==0,2,all)]+nv
v2 <- (1:ne)[apply((vorigin-e2)==0,2,all)]+nv
v3 <- (1:ne)[apply((vorigin-e3)==0,2,all)]+nv
vsort <- sort(c(v1,v2,v3))
v1 <- vsort[1]
v2 <- vsort[2]
v3 <- vsort[3]
nindices[,i4-3] <- c(ind0[1],v1,v2)
nindices[,i4-2] <- c(ind0[2],v1,v3)
nindices[,i4-1] <- c(ind0[3],v2,v3)
nindices[,i4] <- c(v1,v2,v3)
nedges[,ne22+i3] <- c(v1,v2)
nedges[,ne21+i3] <- c(v1,v3)
nedges[,ne2+i3] <- c(v2,v3)
}
list(vertices=nvertices,indices=as.vector(nindices),edges=nedges,nv=nnv,ni=nni,ne=nne)
}
icosa1 <- refine.polyeder(icosa0)
icosa2 <- refine.polyeder(icosa1)
icosa3 <- refine.polyeder(icosa2)
icosa4 <- refine.polyeder(icosa3)
icosa5 <- refine.polyeder(icosa4)
save(icosa0,icosa1,icosa2,icosa3,icosa4,icosa5,file="polyeders.rda",compress = TRUE)
#
#  the file "polyeders.rda" needs to be copied to dti/data/
#
```

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dti documentation built on May 29, 2017, 3:50 p.m.