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In the previous plot, we generated triangles automatically. Here, we will learn how to add triangles manually:

1. Set up data for longitude and latitude in radians:

xy = np.array([[-0.101, 0.872], [-0.080, 0.883], [-0.069, 0.888], 
               [-0.054, 0.890], [-0.045, 0.897], [-0.057, 0.895], 
               [-0.073, 0.900], [-0.087, 0.898],
               [-0.090, 0.904], [-0.069, 0.907]])

2. Convert xy from radians to degrees:

x = np.degrees(xy[:, 0])
y = np.degrees(xy[:, 1])

3. Choose the points to form triangles from xy coordinates converted to degrees:

triangles = np.array([[1, 2, 3], [3, 4, 5], [4, 5, 6], [2, 5, 6], 
                      [6, 7, 8], [6, 8, 9], [0, 1, 7]])

4. Plot the triangulation:

plt.triplot(x, y, triangles, 'go-', lw=1.0)

5. Plot labels and the title:

plt.title('triplot of user-specified triangulation')
plt.xlabel('Longitude (degrees)')
plt.ylabel('Latitude (degrees)')

6. Display the plot on the screen:

plt.show()

Here is how it works:

• xy is an array of coordinates in radians.
• np.degrees() converts radians to degrees; x and y are in radians and are then converted to degrees, where x and y stand for the longitude and latitude values, respectively.

A triangle is an array of three point tuples for each triangle to be plotted. Numbers are indices of the points in x and y (0 to 9, a total of 10 points). The output looks as follows: