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Python Matplotlib drawing contour map

2022-01-31 17:02:12 Little cute in the circle of friends

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 )

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

 Contour map .png

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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      image.png

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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      image.png

    • 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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      image.png

    • 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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      image.png

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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    image.png

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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    image.png

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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image.png

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 ~

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