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// offn.cmd
// Surface Evolver command to print Geomview OFF file with virtual vertices to
// separate films meeting at triple lines, permitting
// local normal calculation for smoothing.
// Usage: offn >>> "filename.off"
// Algorithm: Goes through facets, and for each vertex on a facet
// compares the facet normal to existing virtual vertex normal. If
// none is close enough, a new virtual vertex is created.
// Limits: Assumes no more than 6 virtual vertices are needed at a vertex.
define vertex attribute vircount integer // number of virtual vertices at vertex
define vertex attribute virlist real[6] // ID's of virtual vertices
define vertex attribute virnorm real[18] // virtual normals
define facet attribute virvertex integer[3]
cosine_cutoff := 0.8 // criterion for matching normals
makevir := {
local nx,ny,nz,norm,kk,vn,cosang;
offn_virnum := 0;
set vertex vircount 0;
foreach facet ff where show and color >= 0 do
{ nx := ff.x; ny := ff.y; nz := ff.z;
norm := sqrt(nx^2 + ny^2 + nz^2);
nx := nx/norm; ny := ny/norm; nz := nz/norm;
kk := 1; // which facet vertex
foreach ff.vertex vv do
{ vn := 1;
while ( vn <= vv.vircount ) do
{ cosang := nx*vv.virnorm[3*vn-2] + ny*vv.virnorm[3*vn-1]
+ nz*vv.virnorm[3*vn];
if ( abs(cosang) >= cosine_cutoff ) then break;
vn := vn+1;
};
if ( vn > vv.vircount ) then
{ vv.vircount := vv.vircount + 1;
if ( vv.vircount > 6 ) then
{ printf"Too many virtual vertices at vertex %g facet %g\n",vv.id,ff.id;
return;
};
vv.virlist[vv.vircount] := offn_virnum;
ff.virvertex[kk] := offn_virnum;
offn_virnum := offn_virnum + 1;
vv.virnorm[3*vn-2] := nx;
vv.virnorm[3*vn-1] := ny;
vv.virnorm[3*vn] := nz;
}
else ff.virvertex[kk] := vv.virlist[vn];
kk := kk+1;
}
}
}
flist := {
foreach facet ff where show and color >= 0 do
{ printf "3 %g %g %g\n",ff.virvertex[1],ff.virvertex[2],ff.virvertex[3];
}
}
printvir := {
local vn;
offn_virnum := 0;
foreach facet ff do
{ foreach ff.vertex vv do
{ vn := 1;
while ( vn <= vv.vircount ) do
{ if ( offn_virnum == vv.virlist[vn] ) then
{ printf "%f %f %f\n",vv.x,vv.y,vv.z; // add to output vertex list
offn_virnum := offn_virnum + 1;
break;
};
vn := vn+1;
};
}
}
}
offn := { makevir;
printf "OFF\n%g %g %g\n",offn_virnum,
sum(facet,show and color >= 0),
sum(edge,show and color >= 0);
printvir;
flist
}
/* Usage:
Set cosine_cutoff (default 0.8) for detection of ridges.
Set facet "show" criterion, if desired. Then
offn >>> "filename.off"
*/
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