Drawing contour plots using Plotly in Python

In Python Plotly is called "plotly.py". It is a free and open source plotting library built on top of "plotly.js". It supports over 40 unique chart types. This library is mainly used for financial, geographical, scientific, 3D and data analysis applications.

It can be used to draw various types of charts and graphs, such as scatter plots, line plots, bar plots, box plots, histograms, pie charts, area charts, box plots, histograms, heat maps, Subplots, multiple axes, etc.

Plot installation

Execute the following command at the command prompt to install the plotly module. This is an easy way to install the latest Plotly package from PyPi.

pip install plotly

Contour plot is used to visualize three-dimensional data in a two-dimensional surface by plotting constant z slices, called contours.

It is plotted with the help of the contour function (Z) which is a function of two inputs X and Y (X and Y axis coordinates).

Z = fun(x,y)

The ploty module provides a function called Contour for drawing contour plots.

Contour() function

plotly.graph_objects provides a method contour() to draw contour plots. This function has more than 50 parameters, here we only discuss a few parameters.

grammar

plotly.graph_objects.Contour(z=None,x=None,y=None,arg=None,colorbar=None,hoverinfo=None,x=None,y=Non,**kwargs)

parameter

• z: None by default, a two-dimensional list of values ​​used to calculate contours (z data).

• x: x coordinate, default set to None.

• y: y coordinate, default set to None.

Contour plot using 2D array as z function

Plot a contour plot using a two-dimensional array as the z function.

Example

In this example, we will draw a simple contour plot using a 2D array.

import plotly.graph_objects as go
fig = go.Figure(data = go.Contour(z=[[4.3, 0.2],
   [-1.3, 0.9],
   [-0.32, 7.3],
   [4.6, 0.203]]))
fig.show()

Output

Here the 4X2 array represents the z function.

Contour plot with X and Y coordinates

Draw a contour plot using X and Y coordinates and the z function (2D array).

Example

In this example, we will plot a contour plot using a 2D array and X and Y coordinates.

import plotly.graph_objects as go

fig = go.Figure(data = go.Contour(z=[[4.3, 9, 0.2],
   [-1.3, 2.3, 0.9],
   [-0.32, 7.3, 0.23],
   [4.6, 0.203, 0.34]],
   x=[-8, -3, -2,-1, 0.23], # horizontal axis 
   y=[0, 2, 5, 7, 3]# vertical axis
   ))
fig.show()

Output

The x and y coordinates here represent the horizontal axis and vertical axis respectively.

Use Numpy to draw contour plots

Use numpy to draw a contour map. Here we will use the numpy.meshgrid() function to generate arrays of X and Y coordinates.

Example

The

z function will calculate the sum of the square roots of the x and y values ​​using the numpy.sqrt() function.

import numpy as np
import plotly.graph_objects as go

xlist = np.linspace(-3.0, 3.0, 100)
ylist = np.linspace(-3.0, 3.0, 100)

# create a mesh
X, Y = np.meshgrid(xlist, ylist)
Z = np.sqrt(X**2 + Y**2)

trace = go.Contour(x = xlist, y = ylist, z = Z)
data = [trace]
fig = go.Figure(data)
fig.show()

Output

Contour map with color scale

The color scale is a parameter of the plotly.graph_objects.Contour() function, used to set the color scale.

Example

Let's take an example and set the palette name string "Earth" as the colorscale parameter.

import plotly.graph_objects as go
import numpy as np

def f(x, y):
    return np.sin(x) ** 10 + np.cos(10 + y * x) * np.cos(x)

xlist = np.linspace(-3.0, 3.0, 100)
ylist = np.linspace(-3.0, 3.0, 100)

# A mesh is created with the given co-ordinates by this numpy function
X, Y = np.meshgrid(xlist, ylist)
Z = f(X,Y)

fig = go.Figure(go.Contour(x = xlist, y = ylist, z = Z, colorscale='Earth'))
fig.show()

Output

We plotted contour plots using different z functions.

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