Geometry package: Difference between revisions

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octavesvg = svg ("octave.svg").normalize();

ids      = octavesvg.pathid();

P        = octavesvg.path2polygon (ids{1}, 12)(1:end-1,:);

P        = bsxfun (@minus, P, centroid (P));

Now we have our SVG as a polygon compatible with the Geometry package format. You can plot the polygon using the function {{Codeline|drawPolygon}}.  

drawPolygon (P, "-o");

As you can see the polygon has lots of points. We need to simplify the polygon in order to obtain a mesh of reasonable size. Otherwise gmsh will have problems meshing and the result could be huge (or a segmentation fault :( ). The package geometry comes with a simplification function but as of version 1.4.0, this function is very naïve and wont fix this problem. If you know how to simplify polygons you can contribute!

We are going to reduce the amount of points of the polygon in a drastic and destructive way (i.e. the shape may be considerably damaged). The codes to do so follows, in the future a better procedure will be published here.

Ps = P;  

n  = 1e6;

whos P Ps

P  = Ps;  

The next step is to mesh the interior of the polygon. To do this we could just call {{Codeline|delaunay}} on the polygon and be done with it, but in general such mesh wont be so nice (you will need to add interior points). A very effective way of generating a good mesh is to use the package {{Forge|msh}}, which requires [http://geuz.org/gmsh/ Gmsh] installed in your system. The function {{Codeline|data2geo}} in the Geometry package makes our work very easy:

pkg load msh

filename = tmpnam ();

data2geo (P, meshsize, "output", [filename ".geo"]);

T        = msh2m_gmsh (filename);

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After this code finishes, the structure T contains our mesh. To plot the generated mesh we use the function {{Codeline|pdemesh}} from the {{Forge|fpl}} package. In general is a good idea to use the openGL render (called ''fltk'') to plot meshes.

pkg load fpl  

graphics_toolkit ('fltk')

axis tight

axis equal

The output should look something like this