(materials science learning letters 98) pure Python draws a ridge map full of artistic feeling

itread01 2020-11-16 00:31:44
materials science learning letters pure

> This article sample code and attachments have been uploaded to my `Github` Warehouse [https://github.com/CNFeffery/DataScienceStudyNotes](https://github.com/CNFeffery/DataScienceStudyNotes) # 1 Introduction The following picture may have been seen by many readers , This is the British rock band **Joy Division** stay 1979 His first studio album released in **Unknown Pleasures** Cover , By the artist **Peter Saville** Based on the data map of radio pulsar signals , It has become a symbol of popular culture . Similar diagram 1 Style of , There is also a kind of ** Ridge map **, Based on recording the elevation of the earth's surface ** Elevation data **, We can use the horizontal curve based on the altitude of the actual location , To give a more artistic expression to the terrain of a certain area . And today's article , We will come together on the basis of `Python`, With the choice of color and font , Use short code , You can create art poster level ** Ridge map **. # 2 Based on ridge_map Map the ridge of the mountain We mainly use `matplotlib` And `ridge_map` To complete the creation of a ridge map , Use `pip install ridge_map ` Finish right `ridge_map` After the installation of , Let's start with a very simple example : ```Python from ridge_map import RidgeMap import matplotlib.font_manager as fm import matplotlib.pyplot as plt # Register fonts from local font files font_prop = fm.FontProperties(fname="fonts/UncialAntiqua-Regular.ttf") # Based on the lower left corner of the incoming area 、 Latitude and longitude of upper right corner # To get the original elevation data and draw a ridge map # If you have “ Special Internet skills ”, The waiting time for this step will be short ( RidgeMap(bbox=(-156.250305,18.890695,-154.714966,20.275080), font=font_prop) .plot_map(label="Hawai'i") ) plt.savefig(' Graph 3.png') ``` This is `ridge_map` The basic model for mapping ridges , utilize `matplotlib.font_manager` Register the font to use , And then the drawing area bbox Information and font attributes are passed in `RidgeMap()` Call after `plot_map()` Method to draw . But if you want to make a more customized ridge map like this , You need to know more about it : Let's introduce it by parts : ## 2.1 Data preparation We use `RidgeMap` Accept `bbox` The argument determines the range of the region , The format is `( The longitude of the lower left corner , Lower left latitude , The longitude of the upper right corner , Latitude in the upper right corner )`, It is based on elevation data from **NASA** Of [SRTM](https://www2.jpl.nasa.gov/srtm/) Data sets , The resolution is 1 Arcseconds ( About 30 rice ), It is suitable for north latitude 60° To the south latitude 60° The area between . `ridge_map` The complete process of data preparation is as follows , among `get_elevation_data` Methodical `num_lines` Arguments are used to control the number of horizontal lines corresponding to the returned data , The more detailed , The default is 80;`viewpoint` The argument is used to determine the direction of the compass , The default is `south`: ```Python # initialization rm = RidgeMap(bbox=(-156.250305,18.890695,-154.714966,20.275080), font=font_prop) # Get elevation data online values = rm.get_elevation_data(num_lines=200, viewpoint='north') ``` And what you get is `values` In fact, it is the two-dimensional change of altitude of each horizontal line within the range `numpy` Array : ## 2.2 Data processing Based on the information obtained in the first step , We can use `RidgeMap` Of `preprocess` Method to process , In order to achieve some such as changing the height of the map ratio 、 Low lying area screening function , The main arguments are as follows : > **values**: Pass in the 2D array data obtained in the previous step > > **water_ntile**: Floating point numbers , The scope should be in 0 To 100 Between , As a threshold for data deletion , That is, the height is lower than that of the whole **water_ntile%** Quantile data will be treated as water bodies , So that... Is not shown in the image > > **vertical_ratio**: Used to set the multiple of the original height value to be expanded in the drawing , The bigger, the more exaggerated ```Python values = rm.preprocess(values=values, water_ntile=10, vertical_ratio=240) rm.plot_map(values, label="Hawai'i") plt.savefig(' Graph 6.png') ``` ## 2.3 Drawing images After finishing the above data processing , We can call `plot_map()` Method to draw the ridge map , The main arguments are as follows : > **values**: Processed before it was introduced values > > **label**: Used to set the content of the text label superimposed on the image > > **label_x**:0-1 Floating point number between , Used to determine the ratio of the lower left corner of the text label to the drawing area x coordinates > > **label_y**: Similar **label_x**, Adjust y coordinates > > **label_verticalalignment**: Adjust the vertical alignment of text labels , The default is `'bottom'` > > **label_size**: Control the font size of text labels , The default is 40 > > **line_color**: Set the color of the line , The default is `'black'`, When it comes to `matplotlib` Medium `colormap` The color map mode is turned on when the object is selected > > **kind**: Set color mapping strategy ,`'gradient'` It has nothing to do with height , Color gradient in the vertical direction of the picture ,`'elevation'` Then the color mapping is tied to the height > > **linewidth**: Set line thickness , The default is 2 > > **background_color**: Set the image background color The other arguments are very easy to understand , Here's to highlight the difference `kind` The difference between the results under arguments : - **kind='gradient'** ```Python rm.plot_map(values, label="Hawai'i", kind='gradient', line_color=plt.get_cmap('Reds')) ``` You can see in the `gradient` In mode , The line colors on the whole image follow from top to bottom `colormap` Make a gradient . - **kind='elevation'** ```Python rm.plot_map(values, label="Hawai'i", kind='elevation', line_color=plt.get_cmap('Reds')) plt.savefig(' Graph 8.png') ``` We can see that our line color is based on the height information . ## 2.4 Combine matplotlib Because `ridge_map` Based on `matplotlib`, So we can be like `geopandas` Draw like that , Calling `plot_map` In time `ax` An argument is passed into an existing `Axes` thing , To combine different types of images , Like this simple example : stay get To `ridge_map` After the interesting use of , We can draw anywhere within the legal scope , For example, the following part of Chongqing's downtown area is drawn : ```Python font_prop = fm.FontProperties(fname="fonts/LongCang-Regular.ttf") rm = RidgeMap(bbox=(106.360758,29.385385,106.74734,29.676339), font=font_prop) values = rm.get_elevation_data(num_lines=250, viewpoint='south') values = rm.preprocess(values=values, water_ntile=5, vertical_ratio=90) rm.plot_map(values, label="", kind='elevation', line_color=plt.get_cmap('plasma'), label_size=100) plt.savefig(' Graph 10.png') ``` --- The above is the whole content of this article , You can create creative ridge maps . Welcome to join me in the comments section

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