# ------------------------------------------------------------------------------ # # Gmsh Python tutorial 2 # # Transformations, extruded geometries, volumes # # ------------------------------------------------------------------------------ import gmsh import sys import math # If sys.argv is passed to gmsh.initialize(), Gmsh will parse the command line # in the same way as the standalone Gmsh app: gmsh.initialize(sys.argv) gmsh.model.add("t2") # Copied from `t1.py'... lc = 1e-2 gmsh.model.geo.addPoint(0, 0, 0, lc, 1) gmsh.model.geo.addPoint(.1, 0, 0, lc, 2) gmsh.model.geo.addPoint(.1, .3, 0, lc, 3) gmsh.model.geo.addPoint(0, .3, 0, lc, 4) gmsh.model.geo.addLine(1, 2, 1) gmsh.model.geo.addLine(3, 2, 2) gmsh.model.geo.addLine(3, 4, 3) gmsh.model.geo.addLine(4, 1, 4) gmsh.model.geo.addCurveLoop([4, 1, -2, 3], 1) gmsh.model.geo.addPlaneSurface([1], 1) gmsh.model.geo.synchronize() gmsh.model.addPhysicalGroup(1, [1, 2, 4], 5) gmsh.model.addPhysicalGroup(2, [1], name="My surface") # We can then add new points and curves in the same way as we did in `t1.py': gmsh.model.geo.addPoint(0, .4, 0, lc, 5) gmsh.model.geo.addLine(4, 5, 5) # But Gmsh also provides tools to transform (translate, rotate, etc.) # elementary entities or copies of elementary entities. Geometrical # transformations take a vector of pairs of integers as first argument, which # contains the list of entities, represented by (dimension, tag) pairs. For # example, the point 5 (dimension=0, tag=5) can be moved by 0.02 to the left # (dx=-0.02, dy=0, dz=0) with gmsh.model.geo.translate([(0, 5)], -0.02, 0, 0) # And it can be further rotated by -Pi/4 around (0, 0.3, 0) (with the rotation # along the z axis) with: gmsh.model.geo.rotate([(0, 5)], 0, 0.3, 0, 0, 0, 1, -math.pi / 4) # Note that there are no units in Gmsh: coordinates are just numbers - it's # up to the user to associate a meaning to them. # Point 3 can be duplicated and translated by 0.05 along the y axis by using the # copy() function, which takes a vector of (dim, tag) pairs as input, and # returns another vector of (dim, tag) pairs: ov = gmsh.model.geo.copy([(0, 3)]) gmsh.model.geo.translate(ov, 0, 0.05, 0) # The new point tag is available in ov[0][1], and can be used to create new # lines: gmsh.model.geo.addLine(3, ov[0][1], 7) gmsh.model.geo.addLine(ov[0][1], 5, 8) gmsh.model.geo.addCurveLoop([5, -8, -7, 3], 10) gmsh.model.geo.addPlaneSurface([10], 11) # In the same way, we can translate copies of the two surfaces 1 and 11 to the # right with the following command: ov = gmsh.model.geo.copy([(2, 1), (2, 11)]) gmsh.model.geo.translate(ov, 0.12, 0, 0) print("New surfaces " + str(ov[0][1]) + " and " + str(ov[1][1])) # Volumes are the fourth type of elementary entities in Gmsh. In the same way # one defines curve loops to build surfaces, one has to define surface loops # (i.e. `shells') to build volumes. The following volume does not have holes and # thus consists of a single surface loop: gmsh.model.geo.addPoint(0., 0.3, 0.12, lc, 100) gmsh.model.geo.addPoint(0.1, 0.3, 0.12, lc, 101) gmsh.model.geo.addPoint(0.1, 0.35, 0.12, lc, 102) # We would like to retrieve the coordinates of point 5 to create point 103, so # we synchronize the model, and use `getValue()' gmsh.model.geo.synchronize() xyz = gmsh.model.getValue(0, 5, []) gmsh.model.geo.addPoint(xyz[0], xyz[1], 0.12, lc, 103) gmsh.model.geo.addLine(4, 100, 110) gmsh.model.geo.addLine(3, 101, 111) gmsh.model.geo.addLine(6, 102, 112) gmsh.model.geo.addLine(5, 103, 113) gmsh.model.geo.addLine(103, 100, 114) gmsh.model.geo.addLine(100, 101, 115) gmsh.model.geo.addLine(101, 102, 116) gmsh.model.geo.addLine(102, 103, 117) gmsh.model.geo.addCurveLoop([115, -111, 3, 110], 118) gmsh.model.geo.addPlaneSurface([118], 119) gmsh.model.geo.addCurveLoop([111, 116, -112, -7], 120) gmsh.model.geo.addPlaneSurface([120], 121) gmsh.model.geo.addCurveLoop([112, 117, -113, -8], 122) gmsh.model.geo.addPlaneSurface([122], 123) gmsh.model.geo.addCurveLoop([114, -110, 5, 113], 124) gmsh.model.geo.addPlaneSurface([124], 125) gmsh.model.geo.addCurveLoop([115, 116, 117, 114], 126) gmsh.model.geo.addPlaneSurface([126], 127) gmsh.model.geo.addSurfaceLoop([127, 119, 121, 123, 125, 11], 128) gmsh.model.geo.addVolume([128], 129) # When a volume can be extruded from a surface, it is usually easier to use the # `extrude()' function directly instead of creating all the points, curves and # surfaces by hand. For example, the following command extrudes the surface 11 # along the z axis and automatically creates a new volume (as well as all the # needed points, curves and surfaces). As expected, the function takes a vector # of (dim, tag) pairs as input as well as the translation vector, and returns a # vector of (dim, tag) pairs as output: ov2 = gmsh.model.geo.extrude([ov[1]], 0, 0, 0.12) # Mesh sizes associated to geometrical points can be set by passing a vector of # (dim, tag) pairs for the corresponding points: gmsh.model.geo.mesh.setSize([(0, 103), (0, 105), (0, 109), (0, 102), (0, 28), (0, 24), (0, 6), (0, 5)], lc * 3) # We finish by synchronizing the data from the built-in CAD kernel with the Gmsh # model: gmsh.model.geo.synchronize() # We group volumes 129 and 130 in a single physical group with tag `1' and name # "The volume": gmsh.model.addPhysicalGroup(3, [129, 130], 1, "The volume") # We finally generate and save the mesh: gmsh.model.mesh.generate(3) gmsh.write("t2.msh") # Note that, if the transformation tools are handy to create complex geometries, # it is also sometimes useful to generate the `flat' geometry, with an explicit # representation of all the elementary entities. # # With the built-in CAD kernel, this can be achieved by saving the model in the # `Gmsh Unrolled GEO' format: # # gmsh.write("t2.geo_unrolled"); # # With the OpenCASCADE CAD kernel, unrolling the geometry can be achieved by # exporting in the `OpenCASCADE BRep' format: # # gmsh.write("t2.brep"); # # (OpenCASCADE geometries can also be exported as STEP files.) # It is important to note that Gmsh never translates geometry data into a common # representation: all the operations on a geometrical entity are performed # natively with the associated CAD kernel. Consequently, one cannot export a # geometry constructed with the built-in kernel as an OpenCASCADE BRep file; or # export an OpenCASCADE model as an Unrolled GEO file. # Launch the GUI to see the results: if '-nopopup' not in sys.argv: gmsh.fltk.run() gmsh.finalize()