# Tips and Tricks

Below are a few tips and tricks that you may find useful when you use Mayavi2.

## Using Mayavi in Jupyter notebooks

There are three different ways in which one can embed Mayavi visualizations in a Jupyter notebook. The best way is to use the `'ipy'` backend (which is the default). This backend was first introduced in Mayavi 4.7.0. This backend requires that the ipywidgets and ipyevents packages be installed. It behaves almost exactly like a normal Mayavi UI window and supports any Mayavi/VTK visualization and is fully interactive. This backend relies on VTK’s off screen support and depending on how your VTK is configured may require a windowing system.

There are two other backends, the simplest one is the `'png'` backend which produces images that can be embedded in the notebook. These are static and not interactive.

In between these two extremes is the `'x3d'` backend which displays X3D elements on the notebook. The X3D output produces a fully interactive 3D scene, however, this will not support VTK’s interactive widgets. It does not support transparency and other advanced visualizations either. For information on how to interact with the X3D scene, see here: http://www.x3dom.org/documentation/interaction/

Mayavi ships with some javascript files that can be installed as:

    $ jupyter nbextension install --py mayavi --user

This will install the x3dom Javascript and CSS files locally. Note that you do not need to “enable” the extension or anything after you run the above. For more instructions and options see the Installation of Jupyter Extensions. Doing this allows one to view X3D files without a network connection.

To view Mayavi visualizations on the notebook one should first do:

    from mayavi import mlab
    mlab.init_notebook()

Subequently, one may simply do:

    s = mlab.test_plot3d()
    s

When the `init_notebook` method is called it configures the Mayavi objects so they can be rendered on the Jupyter notebook.

Note

One can call `init_notebook` multiple times if one wishes to change the backend between `ipy`, `png`, and `x3d` for some reason.

There are several optional arguments to `init_notebook`.

- The first is the backend which defaults to `'ipy'`, and can also be set to `'x3d'` or `'png'`.

- One can set the pixel width and height of the figure to create (as integers) (for example `mlab.init_notebook('x3d', 800, 800)`). This only applies to the `x3d` backend. For the `ipy` backend this can be set when creating a new `figure` with the `size` keyword argument.

- The last keyword argument `local` defaults to `True`. When `local=True` it uses javascript files that are distributed along with Mayavi otherwise will require an internet connection to use the x3dom files online. If for some reason the installation of the jupyter nbextension is not working, using `local=False` with an internet connection should work on a modern browser that supports WebGL.

The X3D data is embedded in the notebook and can be shared but if the scenes have a lot of polygons, these files can be large. With the PNG backend, the PNG’s are also embedded and these are smaller files. The PNG backend relies on offscreen rendering working correctly on your platform.

## Off screen rendering

### Avoiding the rendering window

Often you write Mayavi scripts to render a whole batch of images to make an animation or so and find that each time you save an image, Mayavi “raises” the window to make it the active window thus disrupting your work. This is needed since VTK internally grabs the window to make a picture. Occluding the window will also produce either blank or incorrect images.

If you already have a Python script, say `script.py` that sets up your visualization that you run likes so:

    $ mayavi2 -x script.py

Then it is very easy to have this script run offscreen. Simply run it like so:

    $ mayavi2 -x script.py -o

This will run the script in an offscreen, standalone window. On Linux, this works best with VTK-5.2 and above. For more details on the command line arguments supported by the `mayavi2` application, see the Command line arguments section.

When using `mlab` you will want to do this:

    mlab.options.offscreen = True

before you create a figure and it will use an offscreen window for the rendering.

Another option for offscreen rendering would be to click on the scene and set the “Off screen rendering” option on. Or from a script:

    mayavi.engine.current_scene.scene.off_screen_rendering = True

This will stop raising the window. However, this may not be enough. Please see below on the situation on different platforms.

### Platform Summary

- Windows: If you are using win32 then off screen rendering should work well out of the box. All you will need to do is what is given above.

- Linux and the Mac: there are several options to get this working correctly and some major issues to consider:

  If you have VTK-5.2 the offscreen rendering option should let you generate the pictures without worrying about occluding the window. However, you will need VTK-5.2 to get this working properly. There are also situations when this does not always work – try it and if you get blank windows, you have a problem. For example:

      from mayavi import mlab
      mlab.options.offscreen = True
      mlab.test_contour3d()
      mlab.savefig('example.png')

  If this produces a clean image (even if you switch desktops or cover any windows produced), you should be golden. If not you should consider either using a virtual framebuffer or building VTK with Mesa + OSMesa to give you a pure software rendering approach.

### Rendering using the virtual framebuffer

VTK uses openGL for all its rendering. Under any conventional Unix (including Linux), you need an Xserver running to open a GL context (especially if you want hardware acceleration). This might be a problem when rendering on a headless server. As mentioned in the above paragraph, on a desktop, using the default server may also be a problem as it interferes with your ongoing work.

A good workaround is to use the virtual framebuffer X server for X11 like so:

> - Make sure you have the `Xvfb` package installed. For example under Debian and derivatives this is called the `xvfb` package.

> - Create the virtual framebuffer X server like so:

>       Xvfb :1 -screen 0 1280x1024x24 -auth localhost

>   This creates the display “:1” and creates a screen of size 1280x1024 with 24 bpp (the 24bpp is important). For more options check your `Xvfb` man page.

> - Export display to :1 like so (on bash):

>       $ export DISPLAY=:1

> - Now run your Mayavi script. It should run uninterrupted on this X server and produce your saved images.

This probably will have to be fine tuned to suit your taste.

If you want to do this in python. You can use pyvirtualdisplay

    from pyvirtualdisplay import Display
    import os
    display = Display(visible=0, size=(1280, 1024))
    display.start()

Many Linux systems (including Ubuntu and Debian) ship with a helper script xvfb-run for running headless. The following command can run a Python script with Mayavi2 visualizations headless:

    xvfb-run --server-args="-screen 0 1024x768x24" python my_script.py

Beware that you shouldn’t call mlab.show or start the mainloop in the script, elsewhere the script will run endlessly, waiting for interaction in a hidden window.

Note

If you want to use Mayavi without the envisage UI or even a traits UI (i.e. with a pure TVTK window) and do off screen rendering with Python scripts you may be interested in the Offscreen example. This simple example shows how you can use Mayavi without using Envisage or the Mayavi envisage application and still do off screen rendering.

If you are using mlab, outside of the Mayavi2 application, simply set:

    mlab.options.offscreen = True

### Using VTK with Mesa for pure software rendering

Sometimes you might want to run Mayavi/VTK completely headless on a machine with no X server at all and are interested in pure offscreen rendering (for example for usage on the Sage notebook interface). In these cases one could use Mesa’s OSMesa library to render offscreen. The downside is that you will not get any hardware acceleration in this case. Here are brief instructions on how to build VTK to do this.

> - Build a recent version of mesa. 7.0.4 (as of this time) should work as would 7.2. We assume you download MesaLib-7.0.4.tar.bz2.

> - Untar, and change directory to the new directory created. We call this directory `$MESA` henceforth.

> - Run `make configs/linux-x86`, change file as per your configuration. Run `make` to see list of options. Note: 7.2 has a `./configure` script that you can run.

> - Get VTK-5.2 or later (CVS will also work)..

> - Run `ccmake path/to/VTK`.

>   - Now select advanced options ‘t’.

>   - Set `VTK_OPENGL_HAS_OSMESA ON`

>   - Configure: press ‘c’

>   - Set the `OSMESA_INCLUDE_DIR` to the `$MESA/include dir`

>   - Set `OSMESA_LIBRARY` to `$MESA/lib/libOSMesa.so`

>   - Similarly set the `OPENGL_INCLUDE_DIR`, `OPENGL_gl_LIBRARY=$MESA/lib/libGL.so`, `OPENGL_glu_LIBRARY`, and `OPENGL_xmesa_INCLUDE_DIR`.

>   - Set `VTK_USE_OFFSCREEN` to `ON` if you want offscreen all the time, this will never produce an actual mapped VTK window since the default value of the render window’s offscreen rendering ivar will be set to True in this case.

>   - Any other settings like `VTK_USE_GL2PS, USE_RPATH` etc.

>   - Configure again (press ‘c’) and then generate ‘g’.

>   - Note that if you do not want to use `ccmake` and would like to do this from the command line you may also do (for example):

>         cmake \
>         -DVTK_OPENGL_HAS_OSMESA=ON \
>         -DVTK_USE_OFFSCREEN=ON \
>         -DCMAKE_INSTALL_PREFIX=/path/to/vtk-offscreen \
>         -DVTK_WRAP_PYTHON=ON \
>         -DPYTHON_EXECUTABLE=/usr/bin/python2.5 \
>         -DPYTHON_LIBRARY=/usr/lib/libpython2.5.so \
>         -DBUILD_SHARED_LIBS=ON \
>         -DVTK_USE_GL2PS=ON \
>         -DOSMESA_INCLUDE_DIR=/path/to/Mesa-7.2/include/ \
>         -DOSMESA_LIBRARY=/home/path/to/Mesa-7.2/lib64/libOSMesa.so \
>         -DOPENGL_INCLUDE_DIR=/path/to/Mesa-7.2/include \
>         -DOPENGL_gl_LIBRARY=/path/to/Mesa-7.2/lib64/libGL.so \
>         -DOPENGL_glu_LIBRARY=/path/to/Mesa-7.2/lib64/libGLU.so \
>         path/to/VTK/

> - Run `make` and wait till VTK has built. Let us say the build is in `$VTK_BUILD`.

> - Now install VTK or set the `PYTHONPATH` and `LD_LIBRARY_PATH` suitably. Also ensure that `LD_LIBRARY_PATH` points to `$MESA/lib` (if the mesa libs are not installed on the system) this ensures that VTK links to the right GL libs. For example:

>       $ export PYTHONPATH=$VTK_BUILD/bin:$VTK_BUILD/Wrapping/Python``
>       $ export LD_LIBRARY_PATH=$VTK_BUILD/bin:$MESA/lib

>   Now, you should be all set.

Once this is done you should be able to run mlab examples offscreen. This will work without an X display even.

With such a VTK built and running, one could simply build and install mayavi2. To use it in a Sage notebook for example you’d want to set `ETS_TOOLKIT='null'` and set `mlab.options.offscreen = True`. Thats it. Everything should now work offscreen.

Note that if you set `VTK_USE_OFFSCREEN` to `ON` then you’ll by default only get offscreen contexts. If you do want a UI you will want to explicitly set the render window’s `off_screen_rendering` ivar to `False` to force a mapped window. For this reason if you might need to popup a full UI, it might be better to not set `VTK_USE_OFFSCREEN=ON`.

## Extending Mayavi with customizations

A developer may wish to customize Mayavi by adding new sources, filters or modules. These can be done by writing the respective filters and exposing them via a `user_mayavi.py` or a `site_mayavi.py` as described in Customizing Mayavi2. A more flexible and reusable mechanism for doing this is to create a full fledged Mayavi contrib package in the following manner.

> 1. Create a Python package, let’s call it `mv_iitb` (for IIT Bombay specific extensions/customizations). The directory structure of this package can be something like so:

>        mv_iitb/
>                __init__.py
>                user_mayavi.py
>                sources/
>                        ...
>                filters/
>                        ...
>                modules/
>                        ...
>                docs/
>                    ...

>    The two key points to note in the above are the fact that `mv_iitb` is a proper Python package (notice the `__init__.py`) and the `user_mayavi.py` is the file that adds whatever new sources/filters/modules etc. to Mayavi. The other part of the structure is really up to the developer. At the moment these packages can add new sources, filters, modules and contribute any Envisage plugins that the `mayavi2` application will load.

> 2. This package should then be installed somewhere on `sys.path`. Once this is done, users can find these packages and enable them from the Tools->Preferences (the UI will automatically detect the package). The `user_mayavi.py` of each selected package will then be imported next time Mayavi is started, note that this will be usable even from `mlab`.

Any number of such packages may be created and distributed. If they are installed, users can choose to enable them. Internally, the list of selected packages is stored as the `mayavi.contrib_packages` preference option. The following code shows how this may be accessed from a Python script:

    >>> from mayavi.preferences.api import preference_manager
    >>> print preference_manager.root.contrib_packages
    []
    >>> preference_manager.configure_traits() # Pop up a UI.

For more details on how best to write `user_mayavi.py` files and what you can do in them, please refer to the examples/mayavi/user_mayavi.py example. Please pay particular attention to the warnings in that file. It is a very good idea to ensure that the `user_mayavi.py` does not implement any sources/modules/filters and only registers the metadata. This will avoid issues with circular imports.

## Customizing Mayavi2

There are three ways a user can customize Mayavi:

> 1. Via Mayavi contributions installed on the system. This may be done by enabling any found contributions from the Tools->Preferences menu on the Mayavi component, look for the “contribution settings”. Any selected contributions will be imported the next time Mayavi starts. For more details see the Extending Mayavi with customizations section.

> 2. At a global, system wide level via a `site_mayavi.py`. This file is to be placed anywhere on `sys.path`.

> 3. At a local, user level. This is achieved by placing a `user_mayavi.py` in the users `~/.mayavi2/` directory. If a `~/.mayavi2/user_mayavi.py` is found, the directory is placed in `sys.path`.

The files are similar in their content. Two things may be done in this file:

> 1. Registering new sources, modules or filters in the Mayavi registry (`mayavi.core.registry.registry`). This is done by registering metadata for the new class in the registry. See `examples/mayavi/user_mayavi.py` to see an example.

> 2. Adding additional envisage plugins to the mayavi2 application. This is done by defining a function called `get_plugins()` that returns a list of plugins that you wish to add to the mayavi2 application.

The `examples/mayavi/user_mayavi.py` example documents and shows how this can be done. To see it, copy the file to the `~/.mayavi2` directory. If you are unsure where `~` is on your platform, just run the example and it should print out the directory.

Warning

In the `user_mayavi.py` or `site_mayavi.py`, avoid Mayavi imports like `from mayavi.modules.outline import Outline` etc. This is because `user_mayavi` is imported at a time when many of the imports are not complete and this will cause hard-to-debug circular import problems. The `registry` is given only metadata mostly in the form of strings and this will cause no problem. Therefore to define new modules, we strongly recommend that the modules be defined in another module or be defined in a factory function as done in the example `user_mayavi.py` provided.

## Scripting Mayavi without using Envisage

The Standalone example demonstrates how one can use the core Mayavi API without using Envisage. This is useful when you want to minimize dependencies. Offscreen example demonstrates how to use Mayavi without the envisage UI or even a traits UI (i.e. with a pure TVTK window) and do off screen rendering.

## Computing in a thread

Compute in thread example demonstrates how to visualize a 2D numpy array and visualize it as image data using a few modules. It also shows how one can do a computation in another thread and update the Mayavi pipeline once the computation is done. This allows a user to interact with the user interface when the computation is performed in another thread.

## Polling a file and auto-updating Mayavi

Sometimes you have a separate computational process that generates data suitable for visualization. You’d like Mayavi to visualize the data but automatically update the data when the data file is updated by the computation. This is easily achieved by polling the data file and checking if it has been modified. The Poll file example demonstrates this. To see it in action will require that you edit the scalar data in the `examples/data/heart.vtk` data file.

## Serving Mayavi on the network

Say you have a little visualization script and you’d like to run some kind of server where you can script the running Mayavi UI from a TCP/UDP connection. It turns out there is a simple way to do this if you have Twisted installed. Here is a trivial example:

    from mayavi import mlab
    from mayavi.tools import server
    mlab.test_plot3d()
    server.serve_tcp()

There is no need to call `mlab.show()` in the above. The TCP server will listen on port 8007 by default in the above (this can be changed with suitable arguments to `serve_tcp()`). Any data sent to the server is simply exec’d, meaning you can do pretty much anything you want. The names `engine`, `scene`, `camera` and `mlab` are all available and can be scripted with Python code. For example after running the above you can do this:

    $ telnet localhost 8007
    Trying 127.0.0.1...
    Connected to localhost.
    Escape character is '^]'.
    scene.camera.azimuth(45)
    mlab.clf()
    mlab.test_contour3d()
    scene.camera.zoom(1.5)

The nice thing about this is that you do not loose any interactivity of the application and can continue to use its UI as before, any network commands will be simply run on top of this. To serve on a UDP port use the `serve_udp()` function. For more details on the `server` module please look at the source code – it is thoroughly documented.

Warning

While this is very powerful it is also a huge security hole since the remote user can do pretty much anything they want once connected to the server.

### TCP server: the serve_tcp function

### UDP server: the serve_udp function

## Animating a timeseries

If a file that mayavi can load has the form `some_name[0-9]*.ext`, then it is treated as part of a timeseries. For example let us say you have the following files:

    $ ls
    data_01.vti data_02.vti ... data_10.vti

If one loads the file using Mayavi, a slider will show up on the file reader object which can be used to choose an appropriate timestep. There are also buttons to automatically change the timestep. To do this, select the play checkbox. This can also be done programmatically as follows:

    from mayavi import mlab
    src = mlab.pipeline.open('data_01.vti')
    src.play = True

Selecting the “loop” checkbox will loop over the files continuously. If you have multiple files that are part of a timeseries, you can choose the “sync timestep” option. This will sync all the timesteps of the other files that have the same number of timesteps as the current reader. The “Rescan files” button will rescan the files on the disc to find newer ones that are part of the timeseries.

## Animating a visualization

Often users like to animate visualization without affecting the interactive capabilities of the view. For example you may want to rotate the camera continuously, take a snapshot while continuing to interact with the Mayavi UI. To do this one can use the very convenient `animate()` decorator provided with Mayavi. Here is a simple example:

    from mayavi import mlab
    @mlab.animate
    def anim():
        f = mlab.gcf()
        while 1:
            f.scene.camera.azimuth(10)
            f.scene.render()
            yield

    a = anim() # Starts the animation.

Notice the use of `yield` in the above, this is very crucial to this working. This example will continuously rotate the camera without affecting the UI’s interactivity. It also pops up a little UI that lets you start and stop the animation and change the time interval between calls to your function. For more specialized use you can pass arguments to the decorator:

    from mayavi import mlab
    @mlab.animate(delay=500, ui=False)
    def anim():
        # ...

    a = anim() # Starts the animation without a UI.

If you don’t want to import all of `mlab`, the animate decorator is available from:

    from mayavi.tools.animator import animate

Note that to start the event loop, i.e. to get the animation running, you will need to call `show()` if you do not already have a GUI environment running.

Here is another example illustrating the use of the decorator:

    import numpy as np
    from mayavi import mlab

    @mlab.animate(delay = 100)
    def updateAnimation():
        t = 0.0
        while True:
            ball.mlab_source.set(x = np.cos(t), y = np.sin(t), z = 0)
            t += 0.1
            yield

    ball = mlab.points3d(np.array(1.), np.array(0.), np.array(0.))

    updateAnimation()
    mlab.show()

For more details check the documentation of the `animate()` decorator available in the MLab reference. For an example using it, alongside with the visual handy for object-movement animation, see Mlab visual example.

Note

If you want to change the data of an object in an animation, see Animating the data

### Creating a movie from an animation

It is easy to create a movie from either an animation or by playing a timeseries. To do this on the UI, select the Mayavi Scene and navigate to the Movie tab and select the record checkbox. After this, if one animates a timestep via the “play” checkbox referred to in Animating a timeseries, then a stack of images will be created in the directory specified in the movie UI. This will also happen if one runs an animation as discussed in Animating a visualization.

This can also be scripted with mlab for example as follows:

    from mayavi import mlab
    f = mlab.figure()
    f.scene.movie_maker.record = True
    mlab.test_mesh_sphere_anim()

This will create a set of images, one for each step of the animation. The `movie_maker` instance is available on each created scene.

### Animating a series of images

Let’s say you have a stack of PNG or JPEG files that are numbered serially that you want to animate on a Mayavi scene. Here is a simple script (called `img_movie.py`):

    # img_movie.py
    from pyface.timer.api import Timer

    def animate(src, N=10):
        for j in range(N):
            for i in range(len(src.file_list)):
                src.timestep = i
                yield

    if __name__ == '__main__':
        src = mayavi.engine.scenes[0].children[0]
        animator = animate(src)
        t = Timer(250, animator.next)

The `Timer` class lets you call a function without blocking the running user interface. The first argument is the time after which the function is to be called again in milliseconds. The `animate` function is a generator and changes the timestep of the source. This script will animate the stack of images 10 times. The script animates the first data source by default. This may be changed easily.

To use this script do this:

    $ mayavi2 -d your_image000.png -m ImageActor -x img_movie.py

### Making movies from a stack of images

This isn’t really related to Mayavi but is a useful trick nonetheless. Let’s say you generate a stack of images using Mayavi say of the form `anim%03d.png` (i.e. `anim000.png`, `anim001.png` and so on), you can make this into a movie. If you have `mencoder` installed try this:

    $ mencoder "mf://anim%03d.png" -mf fps=10 -o anim.avi \
      -ovc lavc -lavcopts vcodec=msmpeg4v2:vbitrate=500

If you have ffmpeg installed you may try this:

    $ ffmpeg -f image2 -r 10 -i anim%03d.png -sameq anim.mov -pass 2

## Scripting from the command line

The Mayavi application allows for very powerful Command line arguments that lets you build a complex visualization from your shell. What follow is a bunch of simple examples illustrating these.

The following example creates a `ParametricSurface` source and then visualizes glyphs on its surface colored red:

    $ mayavi2 -d ParametricSurface -m Glyph \
    -s"glyph.glyph.scale_factor=0.1" \
    -s"glyph.color_mode='no_coloring'" \
    -s"actor.property.color = (1,0,0)"

Note that `-s"string"` applies the string on the last object (also available as `last_obj`), which is the glyph.

This example turns off coloring of the glyph and changes the glyph to display:

    $ mayavi2 -d ParametricSurface -m Glyph\
    -s"glyph.glyph.scale_factor=0.1" \
    -s"glyph.color_mode='no_coloring'" \
    -s"glyph.glyph_source.glyph_source = last_obj.glyph.glyph_source.glyph_list[-1]"

Note the use of `last_obj` in the above.

## Texture mapping actors

Here is a simple example showing how to texture map an iso-surface with the data that ships with the Mayavi sources (the data files are in the examples directory):

    $ mayavi2 -d examples/tvtk/images/masonry.jpg \
     -d examples/mayavi/data/heart.vti \
     -m IsoSurface \
     -s"actor.mapper.scalar_visibility=False" \
     -s"actor.enable_texture=True"\
     -s"actor.tcoord_generator_mode='cylinder'"\
     -s"actor.texture_source_object=script.engine.current_scene.children[0]"

It should be relatively straightforward to change this example to use a `ParametricSurface` instead and any other image of your choice. Notice how the texture image (`masonry.jpg`) is set in the last line of the above. The image reader is the first child of the current scene and we set it as the `texture_source_object` of the isosurface actor.

## Shifting data and plotting

Sometimes you need to shift/transform your input data in space and visualize that in addition to the original data. This is useful when you’d like to do different things to the same data and see them on the same plot. This can be done with Mayavi using the `TransformData` filter for `StructuredGrid`, `PolyData` and `UnstructuredGrid` datasets. Here is an example using the `ParametricSurface` data source:

    $ mayavi2 -d ParametricSurface \
      -m Outline -m Surface \
      -f TransformData -s "transform.translate(1,1,1)" \
      -s "widget.set_transform(last_obj.transform)" \
      -m Outline -m Surface

If you have an `ImageData` dataset then you can change the origin, spacing and extents alone by using the `ImageChangeInformation` filter. Here is a simple example with the standard Mayavi image data:

    $ mayavi2 -d examples/mayavi/data/heart.vti -m Outline \
    -m ImagePlaneWidget \
    -f ImageChangeInformation \
    -s "filter.origin_translation=(20,20,20)" \
    -m Outline -m ImagePlaneWidget

## Using the `UserDefined` filter

The `UserDefined` filter in Mayavi lets you wrap around existing VTK filters easily. Here are a few examples:

    $ mayavi2 -d ParametricSurface -s "function='dini'" \
    -f UserDefined:GeometryFilter \
    -s "filter.extent_clipping=True" \
    -s "filter.extent = [-1,1,-1,1,0,5]" \
    -f UserDefined:CleanPolyData \
    -m Surface \
    -s "actor.property.representation = 'p'" \
    -s "actor.property.point_size=2"

This one uses a `tvtk.GeometryFilter` to perform extent based clipping of the parametric surface generated. Note the specification of the `-f UserDefined:GeometryFilter`. This data is then cleaned using the `tvtk.CleanPolyData` filter.

Under mlab, the Userdefined can be used to wrap eg a GeometryFilter VTK filter with:

    filtered_obj = mlab.pipeline.user_defined(obj, filter='GeometryFilter')

With mlab, the user_defined function can either take as a filter argument the name of the VTK filter to be used, or an already-instanciated instance of the filter.

Note

With the UserDefined filter, as with most Mayavi filter, the raw TVTK object can be accessed as the filter attribute of the Mayavi filter object.

The Image cursor filter example gives a full example of using the UserDefined filter. The Tvtk segmentation example is a full example of building a complex VTK pipeline with a heavy use of the UserDefined filter.

## Sharing the same data between scenes

If you want to display different views of the same data on different, you will have to create different Mayavi data sources, as a data source can belong on to one scene. However, this does not mean that you need to copy the data, or recreate the source from scratch. The trick is to create a second Mayavi data source pointing to the same underlying VTK dataset, and attach it to another scene (see Data representation in Mayavi for the difference between a Mayavi source and a VTK dataset).

### Using mlab

Every visualization object returned by mlab has a mlab_source attribute, which exposes the VTK dataset as dataset. In addition, the mlab pipeline functions for adding modules know how to use raw VTK datasets. Thus exposing the dataset in a new figure can simply by done by feeding the mlab_source.dataset attribute of a visualization object created by mlab to an mlab.pipeline function:

    from mayavi import mlab
    ctr = mlab.test_contour3d()
    mlab.figure()
    ipw = mlab.pipeline.image_plane_widget(ctr.mlab_source.dataset)
    mlab.show()

The above example creates two figures displaying the same data, one with iso-surfaces, and the other with an image plane widget.

Alternatively, it can be useful to be explicit about the figure that the new module is added onto, rather than using the mlab current figure. This is important to make the code easier to read in situations where the current figure is not clear, for instance in an interactive application, rather than a script:

    new_fig = mlab.figure()
    ipw = mlab.pipeline.image_plane_widget(ctr.mlab_source.dataset, figure=new_fig)

The Volume slicer example shows a complex dialog exposing the same data through different views via mlab.pipeline.

### Using the core Mayavi API

You can also do this fully explicitly by creating the objects yourself through the Mayavi core api, and adding them to the pipeline, rather than using factories:

    import numpy as np
    a = np.random.random((3, 3, 3))
    from mayavi.sources.api import ArraySource, VTKDataSource
    src1 = ArraySource(scalar_data=a)
    engine.add_source(src1)
    engine.new_scene()
    scene2 = engine.current_scene

    # Now create a second data source viewing the same data:
    src2 = VTKDataSource(data=src1.image_data)
    scene2.add_child(src2)

## Changing the interaction with a scene

The default 3D interaction with the scene (left click on the background rotates the scene, right click scales, middle click pans) is not suited for every visualization. For instance, in can be interesting to restrict the movement to 2D, e.g. when viewing an object in the ‘x’ direction. This is done by changing the interactor_style of a scene. Here is an example to use Mayavi as a 2D image viewer:

    from mayavi import mlab
    mlab.test_imshow()
    mlab.view(0, 0)
    fig = mlab.gcf()
    from tvtk.api import tvtk
    fig.scene.interactor.interactor_style = tvtk.InteractorStyleImage()
    mlab.show()

Another useful interactor is the ‘terrain’ interactor, handy to have natural movement in scenes where you want the ‘up’ vector to be always pointing in the ‘z’ direction:

    from mayavi import mlab
    mlab.test_surf()
    fig = mlab.gcf()
    from tvtk.api import tvtk
    fig.scene.interactor.interactor_style = tvtk.InteractorStyleTerrain()
    mlab.show()

VTK has many different interactors. An easy way to list them is to display the VTK class browser (via the help menu, in the mayavi2 application) and to search for “Interactor”. Another option is to tab complete on Ipython, on tvtk.InteractorStyle.

## Accelerating a Mayavi script

You’ve just created a nice Mayavi/mlab script and now want to generate an animation or a series of images. You realize that it is way too slow rendering the images and takes ages to finish. There are two simple ways to speed up the rendering. Let’s assume that `obj` is any Mayavi pipeline object that has a `scene` attribute:

    obj.scene.disable_render = True
    # Do all your scripting that takes ages.
    # ...
    # Once done, do the following:
    obj.scene.disable_render = False

This will speed things up for complex visualizations sometimes by an order of magnitude.

While saving the visualization to an image you can speed up the image generation at the cost of loosing out on anti-aliasing by doing the following:

    obj.scene.anti_aliasing_frames = 0

The default value is typically 8 and the rendered image will be nicely anti-aliased. Setting it to zero will not produce too much difference in the rendered image but any smooth lines will now appear slightly jagged. However, the rendering will be much faster. So if this is acceptable (try it) this is a mechanism to speed up the generation of images.