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Quick start

Contour generator

Firstly create a simple 2x2 grid of z values using Python lists:

>>> z = [[0.0, 0.1], [0.2, 0.3]]

Import the :func:`~contourpy.contour_generator` function and call it to create and return the ContourGenerator object that will be used to contour the z values:

>>> from contourpy import contour_generator
>>> cont_gen = contour_generator(z=z)
>>> cont_gen
<contourpy._contourpy.SerialContourGenerator object at 0x7ff827fc4a30>

The hexadecimal number will be different, it is the address of the `pybind11`_-wrapped C++ object.

Contour lines

Create some contour lines at a z-level of 0.25:

>>> lines = cont_gen.lines(0.25)
>>> lines
[array([[0.5, 1.0],
        [1. , 0.75]])]

The output is a list of lines, here just one line that is a `NumPy`_ array of shape (2, 2) consisting of two (x, y) points from (0.5, 1) to (1, 0.75).

Note

The format of data returned by :meth:`~contourpy.SerialContourGenerator.lines` is controlled by the line_type argument passed to :func:`~contourpy.contour_generator`.

Filled contours

Create some filled contours between the z-levels of 0.15 and 0.25:

>>> filled = cont_gen.filled(0.15, 0.25)
>>> filled
([array([[0. , 1.  ],
         [0. , 0.75],
         [1. , 0.25],
         [1. , 0.75],
         [0.5, 1.  ],
         [0. , 1.  ]])],
 [array([0, 6], dtype=uint32)])

The output data is more complicated, it is a tuple of two lists each of which has a length of one corresponding to a single polygon. The first `NumPy`_ array has shape (6, 2) and is the (x, y) coordinates of the 6 points that make up the polygon; the first and last points are the same. The second `NumPy`_ array is an integer array of offsets into the points array; here the offsets cover the whole length of the points array indicating that it is a single polygon. This is explained further in :ref:`fill_type`.

Note

The format of data returned by :meth:`~contourpy.SerialContourGenerator.filled` is controlled by the filled_type argument passed to :func:`~contourpy.contour_generator`.

Graphical output

It is easier to understand the contour lines and filled contours by looking at graphical output. Here is the full example using the `Matplotlib`_ renderer from the :mod:`contourpy.util` module:

.. plot::
   :source-position: below

   from contourpy import contour_generator
   from contourpy.util.mpl_renderer import MplRenderer as Renderer

   z = [[0.0, 0.1], [0.2, 0.3]]
   cont_gen = contour_generator(z=z)
   lines = cont_gen.lines(0.25)
   filled = cont_gen.filled(0.15, 0.25)

   renderer = Renderer(figsize=(4, 2.5))
   renderer.filled(filled, cont_gen.fill_type, color="gold")
   renderer.lines(lines, cont_gen.line_type, color="red", linewidth=2)
   renderer.show()

Alternatively you can use the `Bokeh`_ renderer from the :mod:`contourpy.util.bokeh_renderer` module. In the example above change the line

from contourpy.util.mpl_renderer import MplRenderer as Renderer

into

from contourpy.util.bokeh_renderer import BokehRenderer as Renderer

Output for the `Bokeh`_ renderer is sent to your web browser.