quad Module

Contour calculation of data on structured grids.

See [1] for definition of structured grid types.

References

[1]Structured grids. (n.d.). Retrieved July 21, 2017, from https://geo-ide.noaa.gov/wiki/index.php?title=Structured_grids

Summary

QuadContourGenerator Contour line/polygon generator.

Classes

Inheritance diagram of QuadContourGenerator
class contours.quad.QuadContourGenerator(x, y, z, formatter=<function numpy_formatter>)[source]

Bases: contours.core.ContourMixin

Contour line/polygon generator.

The default constructor supports general structured (curvilinear) grids. If the grid is more structured consider using one of the other constructors:

Note

This is a wrapper around Matplotlib’s QuadContourGenerator, a highly efficient contour generator written in pure C++.

Example

A contrived example using QuadContourGenerator to compute the area and circumference of a circle and a ring.

>>> from contours.core import shapely_formatter as shapely_fmt
>>> from contours.quad import QuadContourGenerator
>>> import numpy as np
>>> x = np.arange(-1, 1+0.01, 0.01)
>>> y = np.arange(-1, 1+0.01, 0.01)
>>> z = np.sqrt(x[:, np.newaxis]**2 + y[np.newaxis, :]**2)
>>> c = QuadContourGenerator.from_rectilinear(x, y, z, shapely_fmt)
>>> contour = c.filled_contour(max=1.0)
>>> print('Area: {:0.2f}'.format(contour[0].area))
Area: 3.14
>>> print('Length: {:0.2f}'.format(contour[0].length))
Length: 6.28
>>> contour = c.filled_contour(min=0.5, max=1.0)
>>> print('Area: {:0.2f}'.format(contour[0].area))
Area: 2.36
>>> print('Length: {:0.2f}'.format(contour[0].exterior.length))
Length: 6.28
>>> print('Length: {:0.2f}'.format(contour[0].interiors[0].length))
Length: 3.14
Parameters:
  • x (array_like) – x coordinates of each point in z. Must be the same size as z.
  • y (array_like) – y coordinates of each point in z. Must be the same size as z.
  • z (array_like) – The 2-dimensional (possibly curvilinear) grid of data to compute contours for. Masked arrays are supported.
  • formatter (callable) – A conversion function to convert from the internal Matplotlib contour format to an external format. See Formatters for more information.
formatter

callable() – A conversion function to convert from the internal Matplotlib contour format to an external format. See Formatters for more information.

Methods:
from_curvilinear(x, y, z[, formatter]) Construct a contour generator from a curvilinear grid.
from_rectilinear(x, y, z[, formatter]) Construct a contour generator from a rectilinear grid.
from_uniform(z[, origin, step, formatter]) Construct a contour generator from a uniform grid.
contour(level) Get contour lines at the given level.
filled_contour([min, max]) Get contour polygons between the given levels.
classmethod from_curvilinear(x, y, z, formatter=<function numpy_formatter>)[source]

Construct a contour generator from a curvilinear grid.

Note

This is an alias for the default constructor.

Parameters:
  • x (array_like) – x coordinates of each point in z. Must be the same size as z.
  • y (array_like) – y coordinates of each point in z. Must be the same size as z.
  • z (array_like) – The 2-dimensional curvilinear grid of data to compute contours for. Masked arrays are supported.
  • formatter (callable) – A conversion function to convert from the internal Matplotlib contour format to an external format. See Formatters for more information.
Returns:

Initialized contour generator.
Return type:

QuadContourGenerator
classmethod from_rectilinear(x, y, z, formatter=<function numpy_formatter>)[source]

Construct a contour generator from a rectilinear grid.

Parameters:
  • x (array_like) – x coordinates of each column of z. Must be the same length as the number of columns in z. (len(x) == z.shape[1])
  • y (array_like) – y coordinates of each row of z. Must be the same length as the number of columns in z. (len(y) == z.shape[0])
  • z (array_like) – The 2-dimensional rectilinear grid of data to compute contours for. Masked arrays are supported.
  • formatter (callable) – A conversion function to convert from the internal Matplotlib contour format to an external format. See Formatters for more information.
Returns:

Initialized contour generator.
Return type:

QuadContourGenerator
classmethod from_uniform(z, origin=(0, 0), step=(1, 1), formatter=<function numpy_formatter>)[source]

Construct a contour generator from a uniform grid.

Note

The default origin and step values is equivalent to calling matplotlib.axes.Axes.contour() with only the z argument.

Parameters:
  • z (array_like) – The 2-dimensional uniform grid of data to compute contours for. Masked arrays are supported.
  • origin ((number.Number, number.Number)) – The (x, y) coordinate of data point z[0,0].
  • step ((number.Number, number.Number)) – The (x, y) distance between data points in z.
  • formatter (callable) – A conversion function to convert from the internal Matplotlib contour format to an external format. See Formatters for more information.
Returns:

Initialized contour generator.
Return type:

QuadContourGenerator
contour(level)

Get contour lines at the given level.

Parameters:level (numbers.Number) – The data level to calculate the contour lines for.
Returns:The result of the formatter called on the contour at the given level.

Inherited from contours.core.Contour.contour()

filled_contour(min=None, max=None)

Get contour polygons between the given levels.

Parameters:
  • min (numbers.Number or None) – The minimum data level of the contour polygon. If None, numpy.finfo(numpy.float64).min will be used.
  • max (numbers.Number or None) – The maximum data level of the contour polygon. If None, numpy.finfo(numpy.float64).max will be used.
Returns:

The result of the formatter called on the filled contour between min and max.

Inherited from contours.core.Contour.filled_contour()