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# Assembling pipelines with mlab

The plotting functions reviewed above explore only a small fraction of the visualization possibilities of Mayavi. The full power of Mayavi can only be unleashed through the control of the pipeline itself. As described in the An overview of Mayavi section, a visualization in Mayavi is created by loading the data in Mayavi with data source object, optionally transforming the data through Filters, and visualizing it with Modules. The mlab functions build complex pipelines for you in one function, making the right choice of sources, filters, and modules, but they cannot explore all the possible combinations.

Mlab provides a submodule pipeline which contains functions to populate the pipeline easily from scripts. This module is accessible in mlab: mlab.pipeline, or can be imported from enthought.mayavi.tools.pipeline.

When using an mlab plotting function, a pipeline is created: first a source is created from numpy arrays, then modules, and possibly filters, are added. The resulting pipeline can be seen for instance with the mlab.show_pipeline command. This information can be used to create the very same pipeline using directly the pipeline scripting module, as the names of the functions required to create each step of the pipeline are directly linked to the default names of the objects created by mlab on the pipeline. As an example, let us create a visualization using `surf()`:

    import numpy as np
    a = np.random.random((4, 4))
    from enthought.mayavi import mlab
    mlab.surf(a)
    mlab.show_pipeline()

The following pipeline is created:

    Array2DSource
        \__ WarpScalar
                \__ PolyDataNormals
                        \__ Colors and legends
                                \__ Surface

The same pipeline can be created using the following code:

    src = mlab.pipeline.array2d_source(a)
    warp = mlab.pipeline.warp_scalar(src)
    normals = mlab.pipeline.poly_data_normals(warp)
    surf = mlab.pipeline.surface(normals)

## Data sources

The pipeline module contains functions for creating various data sources from arrays. They are fully documented in details in the Mlab pipeline-control reference. We give a small summary of the possibilities here.

mlab distinguishes sources with scalar data, and sources with vector data, but more important, it has different functions to create sets of unconnected points, with data attached to them, or connected data points describing continuously varying quantities that can be interpolated between data points, often called fields in physics or engineering.

Unconnected sources:
| `scalar_scatter()`, `vector_scatter()`
Implicitely-connected sources:
| `scalar_field()`, `vector_field()`, `array2d_source()`
Explicitly-connected sources:
| `line_source()`, `triangular_mesh_source()`

All the mab source factories are functions that take numpy arrays and return the Mayavi source object that was added to the pipeline. However, the implicitely-connected sources require well-shaped arrays as arguments: the data is supposed to lie on a regular, orthogonal, grid of the same shape as the shape of the input array, in other words, the array describes an image, possibly 3 dimensional.

## Modules and filters

For each Mayavi module or filter (see Modules and Filters), there is a corresponding mlab.pipeline function. The name of this function is created by replacing the alternating capitals in the module or filter name by underscores. Thus ScalarCutPlane corresponds to scalar_cut_plane.

In general, the mlab.pipeline module and filter factory functions simply create and connect the corresponding object. However they can also contain addition logic, exposed as keyword arguments. For instance they allow to set up easily a colormap, or to specify the color of the module, when relevant. In accordance with the goal of the mlab interface to make frequent operations simple, they use the keyword arguments to choose the properties of the create object to best suit the requirements. It can be thus easier to use the keyword arguments, when available, than to set the attributes of the objects created. For more information, please check out the docstrings. Full, detailed, usage examples are given in the next subsection.

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