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pythonmatplotlibcolorbar

add a secondary independent axis to the colorbar plot

enter image description hereI tried to add a secondary x axis to the top of the plot as a nm scale which can be obtained from the pixels using a correlation function like, nm = 495.04-x*0.059, is there any idea how to do that, I tried many times but failed... thanks

code:

import os
import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
from matplotlib import cm

data = pd.read_csv('BS3053_BFI.dat', sep='.', delimiter='\t',engine = 'python', skiprows=0, header=None)  

data = pd.DataFrame(data).transpose()
pixel_x = data.shape[1]  # pixels in x direction
pixel_y = data.shape[0]  # pixels in y direction

fig = plt.figure()
ax1 = fig.add_subplot(111)
im = ax1.imshow(data, cmap=plt.cm.gnuplot2,extent=[0,1024,257,0],interpolation=None)# ,,
ax1.set_xlabel('Pixel', fontsize=12)[![enter image description here][1]][1]
ax1.set_ylabel('CCD height', fontsize=12)
ax1.set_ylim([0, 257])
ax1.set_yticklabels([])
ax1.tick_params(direction='in',axis='both', length=.1)
ax1.text(0,259, r'BS3053, Slit width 70 $\mu m$', fontsize=10)

# create an axes on the right side of ax. The width of cax will be 5%
# of ax and the padding between cax and ax will be fixed at 0.05 inch.
divider = make_axes_locatable(ax1)
cax = divider.append_axes("right", size="4%", pad=0.05)
plt.colorbar(im, cax=cax);
plt.show()
Solution

  • Some times, a simple way of thinking could make your life easy... it is solved.

    '''

    import os
import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
from matplotlib import cm
from mpl_toolkits.axes_grid1 import make_axes_locatable 
from matplotlib.ticker import AutoLocator


data = pd.read_csv('BS2350_slit_60um.dat', sep='.', delimiter='\t',engine = 'python', skiprows=0, header=None)  
data = pd.DataFrame(data).transpose()
pixel_x = data.shape[1]  # pixels in x direction
pixel_y = data.shape[0]  # pixels in y direction
fig = plt.figure(figsize=(6.4, 6.4))
ax = fig.add_subplot(111)
ax.set_aspect('auto')
im = ax.imshow(data, cmap=plt.cm.gnuplot2,aspect='equal',extent=[0,1024,257,0],interpolation=None)# ,,
ax.set_xlabel('Pixel', fontsize=12)
ax.set_ylabel('CCD height', fontsize=12)
ax.set_ylim([0, 257])
#ax.set_xticklabels([])
ax.set_yticklabels([])
ax.tick_params(direction='in',axis='both', length=.1)
#ax.text(0,259, r'slit width, 40 $\mu m$, minimum slit height', fontsize=10)
#print(data[1][:])

pixel = np.linspace(0,1024)
def pixelTonm(pixel):
    nm = 495.04-pixel*0.059
    return nm 
def nmTopixel(nm):
    pixel = (495.04-nm) / 0.059
    return pixel
    
ax2 = ax.secondary_xaxis('top', functions=(pixelTonm,nmTopixel))   
ax2.set_xlabel('Wavelength / nm', fontsize=12)
ax2.tick_params(direction='out',axis='x', length=2)

# create an axes on the right side of ax. The width of cax will be 5%
# of ax and the padding between cax and ax will be fixed at 0.05 inch.
divider = make_axes_locatable(ax)
cax = divider.append_axes("right", size="2.5%", pad=0.05)
plt.colorbar(im, cax=cax);
plt.savefig('slit_40um_rf_.jpg') [![Afert adding the second axis on the top, and how it looks like][1]][1]
plt.show()

    '''