gmsh.1

.\" $Id: gmsh.1,v 1.46 2003-03-06 23:01:17 geuzaine Exp $
.TH Gmsh 1 "12 November 2001" "Gmsh > 1.30" "Gmsh Manual Pages"
.UC 4
.\" ********************************************************************
.SH NAME
Gmsh \- an automatic three-dimensional finite element mesh generator
with built-in pre- and post-processing facilities
.\" ********************************************************************
.SH SYNOPSIS
.B gmsh [file(s)] [option(s)]
.\" ********************************************************************
.SH DESCRIPTION
\fIGmsh\fR is an automatic three-dimensional finite element mesh
generator, primarily Delaunay, with built-in pre- and post-processing
facilities. Its primal design goal is to provide a simple meshing tool
for academic test cases with parametric input and up to date
visualization capabilities. One of the strengths of \fIGmsh\fR is its
ability to respect a characteristic length field for the generation of
adapted meshes on lines, surfaces and volumes. These adapted meshes
can be mixed with simple structured (transfinite, elliptic, etc.)
meshes in order to augment the flexibility.
.SS Geometrical entity definition
Parameterized geometries are created by successively defining points,
oriented curves (segments, circles, ellipsis, splines, etc.), oriented
surfaces (plane surfaces, ruled surfaces, etc.)  and volumes. Compound
groups of geometrical entities can be defined, based on these elementary
parameterized and scriptable geometric entities.
.SS Mesh generation
A finite element mesh is a tessellation of a given subset of R^3 by
elementary geometrical elements of various shapes (in this case lines,
triangles, quadrangles, tetrahedra, prisms and hexahedra), arranged in
such a way that two of them intersect, if they do, along a common
face, edge or node, and never otherwise. All the finite element meshes
produced by \fIGmsh\fR as unstructured, even if they were generated in
a structured way. This implies that the elementary geometrical
elements are defined only by an ordered list of their vertices (which
allows the orientation of all their lower order geometrical entities)
but no predefined relation is assumed between any two elementary
elements.
.PP
The procedure follows the same order as for the geometry creation:
curves are discretized first; the mesh of the curves is then used to
mesh the surfaces; then the mesh of the surfaces is used to mesh the
volumes. This automatically assures the continuity of the mesh when,
for example, two surfaces share a common curve. Every meshing step is
constrained by the characteristic length field, which can be uniform,
specified by characteristic length associated to elementary
geometrical entities, or associated to another mesh (the background
mesh).
.PP
For each meshing step (i.e. the discretization of lines, surfaces and
volumes), all structured mesh directives are executed first, and serve
as additional constraints for the unstructured parts. The implemented
Delaunay algorithm is subdivided in the following five steps for
surface/volume discretization:
.TP 4
.B 1.
trivial meshing of a box including the convex polygon/polyhedron
defined by the boundary nodes resulting from the discretization of the
curves/surfaces; 
.TP 4
.B 2.
creation of the initial mesh by insertion of all the nodes on the
curves/surfaces thanks to the Bowyer algorithm; 
.TP 4
.B 3.
boundary restoration to force all the edges/faces of the
curves/surfaces to be present in the initial mesh;
.TP 4
.B 4.
suppression of all the unwanted triangles/tetrahedra (in
particular those containing the nodes of the initial box); 
.TP 4
.B 5.
insertion of new nodes by the Bowyer algorithm until the
characteristic size of each simplex is lower or equal to the
characteristic length field evaluated at the center of its
circumscribed circle/sphere.
.SS External solver interface
External solvers can be interfaced with Gmsh through a socket
mechanism, which permits to easily launch computations either locally
or on remote computers, and to collect and exploit the simulation
results within Gmsh.
.SS Scalar, vector and tensor field visualization
Multiple post-processing scalar or vector maps can be loaded and
manipulated (globally or individually) along with the geometry and the
mesh. Scalar fields are represented by iso-value curves or color maps
and vector fields by three-dimensional arrows or displacement
maps. Post-processor functions include offsets, elevation, interactive
color map modification, range clamping, interactive animation, vector
postscript output, etc. All post-processing options can be accessed
either interactively or through the input ascii files.
.\" ********************************************************************
.SH GEOMETRY OPTIONS
.TP 4
.B \-0
parse all input files, output unrolled geometry, and exit. 
.\" ********************************************************************
.SH MESH OPTIONS
.TP 4
.B \-1
perform the one-dimensional mesh, i.e. discretize all the curves in
the geometry.
.TP 4
.B \-2
perform the two-dimensional mesh, i.e. discretize all the surfaces in
the geometry.
.TP 4
.B \-3
perform the three-dimensional mesh, i.e. discretize all the volumes in
the geometry.
.TP 4
.B \-saveall
save all elements (and discard all physical group definitions).
.TP 4
.B \-o file
specify mesh output file name.
.TP 4
.B \-format msh|unv|gref
set output mesh format (default: msh).
.TP 4
.B \-algo iso|tri|aniso
select the two-dimensional mesh algorithm (default: iso).
.TP 4
.B \-smooth int
set the number of smoothing steps (default value is 0).
.\"   .TP 4
.\"   .B \-degree int
.\"   set the degree of the generated elements (default value is 1).
.TP 4
.B \-scale float
apply a global scaling factor to the model (default value is 1.0).
.TP 4
.B \-meshscale float
apply a global scaling factor to the mesh output (default value is 1.0).
.TP 4
.B \-clscale float
apply a global scaling factor to the mesh characteristic lengths in the
model (default value is 1.0).
.TP 4
.B \-rand float
set random perturbation factor (default: 1.e-4).
.TP 4
.B \-bgm file
load the post-processing view in file as the current background mesh.
.TP 4
.B \-constrain
constrain the background mesh with the characteristic lengths of the
model.
.TP 4
.B \-histogram
print mesh quality histogram.
.TP 4
.B \-interactive
display the 2D mesh construction interactively if the anisotropic mesh
algorithm is selected.
.TP 4
.B \-extrude
use the old extrusion mesh generator.
.TP 4
.B \-recombine
recombine meshes from the old extrusion mesh generator.
.\" ********************************************************************
.SH POST-PROCESSING OPTIONS
.TP 4
.B \-dl
enable OpenGL display lists.
.TP 4
.B \-noview
hide all views at startup.
.TP 4
.B \-link int
choose link mode between post-processing views (default: 0).
.TP 4
.B \-smoothview
smooth views at startup.
.TP 4
.B \-convert file file
convert an ascii view into a binary one.
.\" ********************************************************************
.SH DISPLAY OPTIONS
.TP 4
.B \-nodb
suppress the double buffer. Use this options if you use \fIGmsh\fR on
a remote host without GLX.
.TP 4
.B \-alpha
enable alpha blending.
.TP 4
.B \-notrack
don't use trackball mode for rotations.
.TP 4
.B \-display disp
specify display.
.TP 4
.B \-perspective
use perspective instead of orthographic projection.
.\" ********************************************************************
.SH OTHER OPTIONS
.TP 4
.B \-a, \-g, \-m, \-s, \-p
start in automatic, geometry, mesh, solver or post-processing mode
(default: automatic).
.TP 4
.B \-string string
parse string before project file.
.TP 4
.B \-option file
parse option file before GUI creation.
.TP 4
.B \-v int
set verbosity level (default: 2).
.TP 4
.B \-version
show version number.
.TP 4
.B \-info
show detailed version information.
.TP 4
.B \-help
show help message.
.\" ********************************************************************
.SH AUTHORS
Christophe Geuzaine (geuzaine@acm.caltech.edu) and Jean-Francois
Remacle (Remacle@scorec.rpi.edu). 
.\" ********************************************************************
.SH SEE ALSO
.BR getdp (1),
.br
Gmsh examples (\fI/usr/doc/gmsh-*/\fR),
.br
Gmsh homepage (\fIhttp://www.geuz.org/gmsh/\fR).