polymerge(1)

NAME

polymerge - merge coincident vertices, collinear edges,

coplanar faces in an OOGL OFF object

SYNOPSIS

polymerge   [-v   vertex_thresh]   [-e   edge_thresh]  [-f
face_thresh] [-V] [-E] [-F] [-d] [-b] [inputfile.off]

DESCRIPTION

Polymerge eliminates redundancies from polyhedral objects

in OOGL's OFF format, and writes another OFF object to its stan

dard output. (Optionally it can produce instead an input file

for Brakke's Evolver.) Specifically, it combines nearly-coinci

dent vertices, nearly-collinear edges, and nearly-coplanar faces.

Vertices which aren't used on any face are deleted, as are faces

with less than three vertices. Thresholds for approximate equal

ity are adjustable from the command line. Options are:

-v vertex_thresh

Merge vertices when they're closer than

vertex_thresh apart; the default is .00001.

-V Don't attempt to merge vertices.

-e edge_thresh

Merge edges where |sin(vertex_angle)| <

edge_thresh; the default is When edges are merged, the corre

sponding vertex is removed.

-E Don't attempt to merge edges. (4OFF edges are nev

er merged.)

-f face_thresh

Merge faces sharing an edge where the faces are

nearly coplanar: when |sin(angle_between_face_normal_vectors)| <

face_thresh. The default is .03, or about two degrees. Note

that merging can create faces which are concave polygons.

-F Don't attempt to merge faces. (4OFF faces are never

merged.)

-b Produce an output file in .fe format for Brakke's

Surface Evolver, instead of a new OFF file.

-d Include debugging information as comments in the

new OFF object. The comments indicate which vertices and faces

in the original object correspond to which in the new one. Mes

sages include:

# Vtx nnn->mmm

Merged vertices nnn and mmm (both indices in the

original object).

# Merged face nnn into mmm (vertices vvv www) n1.n2 s

Faces nnn and mmm in the original object were

merged; their common edge joined original vertices vvv and www.

The cosine of the angle between the face normals was s.

vertex coordinates # newvertno [order] # oldvertno

Each vertex written appears with its new index, its

order (number of edges touching that vertex), and its old index

(index of a corresponding vertex in the original object).

face description # oldvertno ...

For each new face, with N vertices after reduction,

the comment indicates N corresponding vertices in the original

object.

AUTHOR

Stuart Levy, Geometry Center, University of Minnesota

SEE ALSO

anytooff(1), offconsol(1)

BUGS

Coplanar faces are merged even if they were assigned dif

ferent colors. Should be able to handle binary OFF objects, but

this hasn't been tested.

Geometry Center 25 July 1993

POLYMERGE(1)