This is my participation 11 The fourth of the yuegengwen challenge 15 God , Check out the activity details ：2021 One last more challenge

Preface

We were in the past matplotlib.pyplot() Method learning , By now we have been able to draw a line chart 、 Histogram 、 Scatter and other regular charts （ The contents of previous periods are as follows , You can easily view the contents of previous periods ）

• matplotlib The module overview ： Yes matplotlib Summarize the common methods of the module

• matplotlib Module bottom principle ： Yes matplotlib Module script layer 、 The art layer and the back-end layer learn if they work

• matplotlib Draw line chart ： Summarize the properties of the polyline

• matplotlib Draw a histogram ： Summarize the related attributes of the histogram

• matplotlib Draw histogram ： Histogram related attributes are summarized

• matplotlib Draw a scatter plot ： Summarize the related attributes of scatter chart

stay matplotlib.pyplot In addition to drawing regular charts, such as broken lines 、 Columnar 、 Take it easy and wait , It can also draw the contour map commonly used in geographical plane display

In this issue , We will study in detail matplotlib Drawing contour map related attributes of learning ,let's go~

1. Contour map Overview

• What is a contour map ？

  • Contour map is also called horizontal map , adopt 2D Form show 3D Graph of images
  • Contour map is also called contour line map , Connect the points with the same surface height into a loop line and display it on the plane curve
  • Contour map is also called Z Slice , The dependent variable Z And independent variables X,Y Change and change
  • The contour map can be divided into the first curve 、 Meter curve 、 Intermediate curve and auxiliary curve

• Contour map common scenes

  • Contour maps are often used to show the terrain of a place
  • The contour map can also calculate the height of local mountains
  • Contour maps are often used in geology 、 Drawn by geographical survey
  • Contour maps can also be used to draw circles 、 Mathematical formulas such as ellipse show

• To draw a contour map

  1. Import matplotlib.pyplot modular
  2. Prepare the data , have access to numpy/pandas Collating data
  3. call pyplot.contour() perhaps pyplot.contourf() Draw contours

• The case shows

  Contour map drawing needs the help of many trigonometric functions learned in high school 、 Exponential function and other formulas , In this case, we use the contour method to summarize circles

  • Case data preparation

    • np.arrage() Prepare a series of continuous data
    • np.meshgrid() Convert data into a matrix

    import numpy as np
    #  Define a continuous set of data 
    
    x_value = np.arange(-5,5,0.1)
    y_value = np.arange(-5,5,0.1)
    
    #  Convert to matrix data 
    x,y = np.meshgrid(x_value,y_value)
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  • Draw contours

    
    import matplotlib.pyplot as plt
    
    plt.contour(x,y,z)
    
    plt.title("Display Contour")
    plt.xlabel("x(m)")
    plt.ylabel("y(m)")
    
    plt.show()
    
    plt.show()
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2. Contour map properties

• Set the contour color

  • keyword ：colors
  • Value range :
    • English words for color ： Like red "red"
    • Abbreviations of words indicating color, such as ： Red "r", yellow "y"
    • RGB Format ： Hexadecimal format, such as "#88c999";(r,g,b) Tuple form
    • You can also pass in a color list

• Set contour transparency ：

  • keyword ：alpha
  • The default is 1
  • The value range is ：0~1

• Sets the contour color level

  • keyword ：cmap
  • colors and cmap Two keywords cannot be provided at the same time
  • The value is ： The registered color indicates
    • In the form of ：" color table _r"
    • Commonly used ：'Accent', 'Accent_r', 'Blues', 'Blues_r', 'BrBG', 'BrBG_r', 'BuGn', 'BuGn_r', 'BuPu', 'BuPu_r', 'CMRmap', 'CMRmap_r', 'Dark2', 'Dark2_r', 'GnBu', 'GnBu_r', 'Greens'

• Sets the contour width

  • keyword ：linewidths
  • The default contour width is 1.5
  • The value can be float Type or list

• Set the contour style

  • keyword ：linestyles
  • The default value is ：solid
  • The value is optional ：{None, 'solid', 'dashed', 'dashdot', 'dotted'}
  • linestyles by None When the line is monochrome , The lines with negative contour will be set to dashed

• We added some attributes to the contour map in the previous section

  • The line is red , The line width gradually increases , The line style is dashed, Transparency set to 0.5

    ```python
    plt.contour(x,y,z,colors="r",
    linestyles="dashed",
    linewidths=np.arange(0.5,4,0.5),alpha=0.5)
    ```
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  • Pass in colors list

    plt.contour(x,y,z,
    colors=('r','green','blue',(1,1,0),"#afeeee","0.5"),
    linewidths=np.arange(0.5,4,0.5))
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  • Is a contour map , Set up cmap It's red

    z = np.exp(-x**2-y**2)
    z1 = np.exp(-(x-1)**2-(y-1)**2)
    Z = (z-z1)*2
    
    plt.contour(x,y,Z,
    cmap='afmhot_r',
    linewidths=np.arange(0.5,4,0.5))
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3. Show outline labels

When we look at the contour map , The outline tab will help us better view the chart . Add outline labels , We need the help of clabe

• pyplot.contour() Method of drawing contour lines , Returns the QuadContourset

• QuadContourset contain level The list of data

• Use pyplot.clabel() Accept level List data is marked on contour lines

  
  x_value = np.arange(-3,3,0.025)
  y_value = np.arange(-3,3,0.025)
  
  x,y = np.meshgrid(x_value,y_value)
  
  z = (1-x**2+y**5)*np.exp(-x**2-y**2)
  
  cs = plt.contour(x,y,z,cmap="Blues_r",linewidths=np.arange(0.5,4,0.5))
  
  plt.clabel(cs,fontsize=9,inline=True)
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4. Fill color

Usually in contour plots , Different areas are filled with different colors , Help us better understand when looking at the chart

• Use pyplot.contourf() Contrast the contour of the same area for filling color

  z = (1-x**2+y**5)*np.exp(-x**2-y**2)
  
  cs = plt.contour(x,y,z,10,colors="b",linewidths=0.5)
  
  plt.clabel(cs,fontsize=12,inline=True)
  
  plt.contourf(x,y,z,10,cmap="Blues_r",alpha=0.75)
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5. Add color bar description

We can use pyplot.colorbar() Method to add a color bar description

z = (x**2+y**5)*np.exp(-x**2-y**2)
z1 = np.exp(-(x-1)**2-(y-1)**2)
Z = (z-z1)*2

cs = plt.contour(x,y,Z,10,colors="black",linewidths=0.5)

plt.clabel(cs,fontsize=12,inline=True)

plt.contourf(x,y,Z,10,cmap="afmhot_r",alpha=0.5)

plt.colorbar(shrink=0.8)
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summary

In this issue , Yes matplotlib.pyplot Method of drawing contour lines contour and contourf Learning related attributes . When drawing contour maps , We need to do trigonometric functions 、 Exponential function 、 Have a little knowledge of sine and cosine functions , To draw the chart you want

During the study of this section , High school math knowledge is returned to the teacher , Feel the head , Why did you lose your hair again

The above is the content of this issue , Welcome big guys to praise and comment , See you next time ~