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// -----------------------------------------------------------------------------
//
// Gmsh C++ tutorial 13
//
// Remeshing an STL file without an underlying CAD model
//
// -----------------------------------------------------------------------------
#include <set>
#include <cmath>
#include <gmsh.h>
int main(int argc, char **argv)
{
gmsh::initialize();
auto createGeometryAndMesh = []()
{
gmsh::model::add("t13");
// Let's merge an STL mesh that we would like to remesh (from the parent
// directory):
try {
gmsh::merge("../t13_data.stl");
} catch(...) {
gmsh::logger::write("Could not load STL mesh: bye!");
return;
}
// We first classify ("color") the surfaces by splitting the original
// surface along sharp geometrical features. This will create new discrete
// surfaces, curves and points.
// Angle between two triangles above which an edge is considered as sharp,
// retrieved from the ONELAB database (see below):
std::vector<double> n;
gmsh::onelab::getNumber("Parameters/Angle for surface detection", n);
double angle = n[0];
// For complex geometries, patches can be too complex, too elongated or too
// large to be parametrized; setting the following option will force the
// creation of patches that are amenable to reparametrization:
gmsh::onelab::getNumber
("Parameters/Create surfaces guaranteed to be parametrizable", n);
bool forceParametrizablePatches = n[0] ? true : false;
// For open surfaces include the boundary edges in the classification process:
bool includeBoundary = true;
// Force curves to be split on given angle:
double curveAngle = 180;
gmsh::model::mesh::classifySurfaces(angle * M_PI / 180., includeBoundary,
forceParametrizablePatches,
curveAngle * M_PI / 180.);
// Create a geometry for all the discrete curves and surfaces in the mesh,
// by computing a parametrization for each one
gmsh::model::mesh::createGeometry();
// Note that if a CAD model (e.g. as a STEP file, see `t20.cpp') is
// available instead of an STL mesh, it is usually better to use that CAD
// model instead of the geometry created by reparametrizing the
// mesh. Indeed, CAD geometries will in general be more accurate, with
// smoother parametrizations, and will lead to more efficient and higher
// quality meshing. Discrete surface remeshing in Gmsh is optimized to
// handle dense STL meshes coming from e.g. imaging systems, where no CAD is
// available; it is less well suited for the poor quality STL triangulations
// (optimized for size, with e.g. very elongated triangles) that are usually
// generated by CAD tools for e.g. 3D printing.
// Create a volume from all the surfaces
std::vector<std::pair<int, int> > s;
gmsh::model::getEntities(s, 2);
std::vector<int> sl;
for(auto surf : s) sl.push_back(surf.second);
int l = gmsh::model::geo::addSurfaceLoop(sl);
gmsh::model::geo::addVolume({l});
gmsh::model::geo::synchronize();
// We specify element sizes imposed by a size field, just because we can :-)
int f = gmsh::model::mesh::field::add("MathEval");
gmsh::onelab::getNumber("Parameters/Apply funny mesh size field?", n);
if(n[0])
gmsh::model::mesh::field::setString(f, "F", "2*Sin((x+y)/5) + 3");
else
gmsh::model::mesh::field::setString(f, "F", "4");
gmsh::model::mesh::field::setAsBackgroundMesh(f);
gmsh::model::mesh::generate(3);
};
// Create ONELAB parameters with remeshing options:
gmsh::onelab::set(R"( [
{
"type":"number",
"name":"Parameters/Angle for surface detection",
"values":[40],
"min":20,
"max":120,
"step":1
},
{
"type":"number",
"name":"Parameters/Create surfaces guaranteed to be parametrizable",
"values":[0],
"choices":[0, 1]
},
{
"type":"number",
"name":"Parameters/Apply funny mesh size field?",
"values":[0],
"choices":[0, 1]
}
] )");
// Create the geometry and mesh it:
createGeometryAndMesh();
// Launch the GUI and handle the "check" event to recreate the geometry and mesh
// with new parameters if necessary:
auto checkForEvent = [=]() -> bool {
std::vector<std::string> action;
gmsh::onelab::getString("ONELAB/Action", action);
if(action.size() && action[0] == "check") {
gmsh::onelab::setString("ONELAB/Action", {""});
createGeometryAndMesh();
gmsh::graphics::draw();
}
return true;
};
std::set<std::string> args(argv, argv + argc);
if(!args.count("-nopopup")) {
gmsh::fltk::initialize();
while(gmsh::fltk::isAvailable() && checkForEvent())
gmsh::fltk::wait();
}
gmsh::finalize();
return 0;
}
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