"""
Contours
========

The :meth:`pygmt.Figure.contour` method can plot contour lines from a table of
points by direct triangulation. The data for the triangulation can be provided
using one of three methods:

#. ``x``, ``y``, ``z`` 1-D :class:`numpy.ndarray` data columns.
#. ``data`` 2-D :class:`numpy.ndarray` data matrix with 3 columns corresponding
   to ``x``, ``y``, ``z``.
#. ``data`` path string to a file containing the ``x``, ``y``, ``z`` in a
   tabular format.

The parameters ``levels`` and ``annotation`` set the intervals of the contours
and the annotation on the contours respectively.

In this example we supply the data as 1-D :class:`numpy.ndarray` with the
``x``, ``y``, and ``z`` parameters and draw the contours using a 0.5p pen with
contours every 10 ``z`` values and annotations every 20 ``z`` values.
"""

# %%
import numpy as np
import pygmt

# build the contours underlying data with the function z = x^2 + y^2
X, Y = np.meshgrid(np.linspace(-10, 10, 50), np.linspace(-10, 10, 50))
Z = X**2 + Y**2
x, y, z = X.flatten(), Y.flatten(), Z.flatten()


fig = pygmt.Figure()
fig.contour(
    region=[-10, 10, -10, 10],
    projection="X10c/10c",
    frame="ag",
    pen="0.5p",
    # pass the data as 3 1-D data columns
    x=x,
    y=y,
    z=z,
    # set the contours z values intervals to 10
    levels=10,
    # set the contours annotation intervals to 20
    annotation=20,
)
fig.show()