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# Structured grid example

An example of how to generate a structured grid dataset using numpy arrays. Also shown is a way to visualize this data with the mayavi2 application.

The script can be run like so:

    $ mayavi2 -x structured_grid.py

Alternatively, it can be run as:

    $ python structured_grid.py

Source code: structured_grid.py

    # Authors: Eric Jones <eric at enthought dot com>
    #          Prabhu Ramachandran <prabhu at aero dot iitb dot ac dot in>
    # Copyright (c) 2007, Enthought, Inc.
    # License: BSD style.

    import numpy as np
    from numpy import cos, sin, pi
    from enthought.tvtk.api import tvtk
    from enthought.mayavi.scripts import mayavi2

    def generate_annulus(r=None, theta=None, z=None):
        """ Generate points for structured grid for a cylindrical annular
            volume.  This method is useful for generating a structured
            cylindrical mesh for VTK (and perhaps other tools).

            Parameters
            ----------
            r : array : The radial values of the grid points.
                        It defaults to linspace(1.0, 2.0, 11).

            theta : array : The angular values of the x axis for the grid
                            points. It defaults to linspace(0,2*pi,11).

            z: array : The values along the z axis of the grid points.
                       It defaults to linspace(0,0,1.0, 11).

            Return
            ------
            points : array
                Nx3 array of points that make up the volume of the annulus.
                They are organized in planes starting with the first value
                of z and with the inside "ring" of the plane as the first
                set of points.  The default point array will be 1331x3.
        """
        # Default values for the annular grid.
        if r is None: r = np.linspace(1.0, 2.0, 11)
        if theta is None: theta = np.linspace(0, 2*pi, 11)
        if z is None: z = np.linspace(0.0, 1.0, 11)

        # Find the x values and y values for each plane.
        x_plane = (cos(theta)*r[:,None]).ravel()
        y_plane = (sin(theta)*r[:,None]).ravel()

        # Allocate an array for all the points.  We'll have len(x_plane)
        # points on each plane, and we have a plane for each z value, so
        # we need len(x_plane)*len(z) points.
        points = np.empty([len(x_plane)*len(z),3])

        # Loop through the points for each plane and fill them with the
        # correct x,y,z values.
        start = 0
        for z_plane in z:
            end = start + len(x_plane)
            # slice out a plane of the output points and fill it
            # with the x,y, and z values for this plane.  The x,y
            # values are the same for every plane.  The z value
            # is set to the current z
            plane_points = points[start:end]
            plane_points[:,0] = x_plane
            plane_points[:,1] = y_plane
            plane_points[:,2] = z_plane
            start = end

        return points

    # Make the data.
    dims = (51, 25, 25)
    # Note here that the 'x' axis corresponds to 'theta'
    theta = np.linspace(0, 2*np.pi, dims[0])
    # 'y' corresponds to varying 'r'
    r = np.linspace(1, 10, dims[1])
    z = np.linspace(0, 5, dims[2])
    pts = generate_annulus(r, theta, z)
    # Uncomment the following if you want to add some noise to the data.
    #pts += np.random.randn(dims[0]*dims[1]*dims[2], 3)*0.04
    sgrid = tvtk.StructuredGrid(dimensions=dims)
    sgrid.points = pts
    s = np.sqrt(pts[:,0]**2 + pts[:,1]**2 + pts[:,2]**2)
    sgrid.point_data.scalars = np.ravel(s.copy())
    sgrid.point_data.scalars.name = 'scalars'

    # Uncomment the next two lines to save the dataset to a VTK XML file.
    #w = tvtk.XMLStructuredGridWriter(input=sgrid, file_name='sgrid.vts')
    #w.write()

    # View the data.
    @mayavi2.standalone
    def view():
        from enthought.mayavi.sources.vtk_data_source import VTKDataSource
        from enthought.mayavi.modules.api import Outline, GridPlane

        mayavi.new_scene()
        src = VTKDataSource(data=sgrid)
        mayavi.add_source(src)
        mayavi.add_module(Outline())
        g = GridPlane()
        g.grid_plane.axis = 'x'
        mayavi.add_module(g)
        g = GridPlane()
        g.grid_plane.axis = 'y'
        mayavi.add_module(g)
        g = GridPlane()
        g.grid_plane.axis = 'z'
        mayavi.add_module(g)

    if __name__ == '__main__':
        view()

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