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41 results

t12.py

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  • x5.py 3.63 KiB
    # -----------------------------------------------------------------------------
    #
    #  Gmsh Python extended tutorial 5
    #
    #  Additional geometrical data: parametrizations, normals, curvatures
    #
    # -----------------------------------------------------------------------------
    
    import gmsh
    import sys
    import math
    
    gmsh.initialize(sys.argv)
    
    # The API provides access to geometrical data in a CAD kernel agnostic manner.
    
    # Let's create a simple CAD model by fusing a sphere and a cube, then mesh the
    # surfaces:
    gmsh.model.add("x5")
    s = gmsh.model.occ.addSphere(0, 0, 0, 1)
    b = gmsh.model.occ.addBox(0.5, 0, 0, 1.3, 2, 3)
    gmsh.model.occ.fuse([(3, s)], [(3, b)])
    gmsh.model.occ.synchronize()
    gmsh.model.mesh.generate(2)
    
    # We can for example retrieve the exact normals and the curvature at all the
    # mesh nodes (i.e. not normals and curvatures computed from the mesh, but
    # directly evaluated on the geometry), by querying the CAD kernels at the
    # corresponding parametric coordinates.
    normals = []
    curvatures = []
    
    # For each surface in the model:
    for e in gmsh.model.getEntities(2):
        # Retrieve the surface tag
        s = e[1]
    
        # Get the mesh nodes on the surface, including those on the boundary
        # (contrary to internal nodes, which store their parametric coordinates,
        # boundary nodes will be reparametrized on the surface in order to compute
        # their parametric coordinates, the result being different when
        # reparametrized on another adjacent surface)
        tags, coord, param = gmsh.model.mesh.getNodes(2, s, True)
    
        # Get the surface normals on all the points on the surface corresponding to
        # the parametric coordinates of the nodes
        norm = gmsh.model.getNormal(s, param)
    
        # In the same way, get the curvature
        curv = gmsh.model.getCurvature(2, s, param)
    
        # Store the normals and the curvatures so that we can display them as
        # list-based post-processing views
        for i in range(0, len(coord), 3):
            normals.append(coord[i])
            normals.append(coord[i + 1])
            normals.append(coord[i + 2])
            normals.append(norm[i])
            normals.append(norm[i + 1])
            normals.append(norm[i + 2])
            curvatures.append(coord[i])
            curvatures.append(coord[i + 1])
            curvatures.append(coord[i + 2])
            curvatures.append(curv[i // 3])
    
    # Create a list-based vector view on points to display the normals, and a scalar
    # view on points to display the curvatures
    vn = gmsh.view.add("normals")
    gmsh.view.addListData(vn, "VP", len(normals) // 6, normals)
    gmsh.view.option.setNumber(vn, 'ShowScale', 0)
    gmsh.view.option.setNumber(vn, 'ArrowSizeMax', 30)
    gmsh.view.option.setNumber(vn, 'ColormapNumber', 19)
    vc = gmsh.view.add("curvatures")
    gmsh.view.addListData(vc, "SP", len(curvatures) // 4, curvatures)
    gmsh.view.option.setNumber(vc, 'ShowScale', 0)
    
    # We can also retrieve the parametrization bounds of model entities, e.g. of
    # curve 5, and evaluate the parametrization for several parameter values:
    bounds = gmsh.model.getParametrizationBounds(1, 5)
    N = 20
    t = [bounds[0][0] + i * (bounds[1][0] - bounds[0][0]) / N for i in range(N)]
    xyz1 = gmsh.model.getValue(1, 5, t)
    
    # We can also reparametrize curve 5 on surface 1, and evaluate the points in the
    # parametric plane of the surface:
    uv = gmsh.model.reparametrizeOnSurface(1, 5, t, 1)
    xyz2 = gmsh.model.getValue(2, 1, uv)
    
    # Hopefully we get the same x, y, z coordinates!
    if max([abs(a - b) for (a, b) in zip(xyz1, xyz2)]) < 1e-12:
        gmsh.logger.write('Evaluation on curve and surface match!')
    else:
        gmsh.logger.write('Evaluation on curve and surface do not match!', 'error')
    
    # Launch the GUI to see the results:
    if '-nopopup' not in sys.argv:
        gmsh.fltk.run()
    
    gmsh.finalize()