The code reference on my stackoverflow question 'Tracking positions of points after piecewiseAffineTransformaiton.'

Stackoverflow_question

#!/usr/bin/env python2
# -*- coding: utf-8 -*-
"""
Created on Mon Mar 20 09:49:48 2017

@author: po-hsuan
"""

import numpy as np
import matplotlib.pyplot as plt
from skimage.transform import PiecewiseAffineTransform, warp
from skimage import data
    
def find_map_index(x,y, rows, cols):
        # in PIL warping map coordinate

    return  rows*y + x 

def find_linspace_index(x,y,lin_rows,lin_cols):
    print 'linrows', lin_rows
    print 'atual, ', x, y 
    # find the nearest elemet to x, y in the linspaces
    # convert to warpping cooridnates

    index_x = np.where(lin_rows > x)[0][0]
    index_y = np.where(lin_cols > y)[0][0]
   
    print 'indeces, ', index_x, index_y
    print 'inline ', lin_rows[index_x], lin_cols[index_y]
    return index_x, index_y 

if __name__ == '__main__':
    #---my label positions
    
    ori_labelx = [  100, 100, 300, 300]
    ori_labely = [  100, 300, 100, 300]
    #---
    
    image = data.astronaut()
    rows, cols = image.shape[0], image.shape[1]
    
    lin_cols = np.linspace(0, cols, 50)
    lin_rows = np.linspace(0, rows, 50)
    src_rows, src_cols = np.meshgrid(lin_rows, lin_cols)
    src = np.dstack([src_cols.flat, src_rows.flat])[0]
    
    # find the indices of the coordinates in linspace
    index_x = range(4)
    index_y = range(4)
    for i, (x, y) in enumerate (zip(ori_labelx, ori_labely)):
        index_x[i], index_y[i] = find_linspace_index(x, y, lin_rows, lin_cols)   
    
    # add sinusoidal oscillation to row coordinates
    dst_rows = src[:, 1] - np.sin(np.linspace(0, 3 * np.pi, src.shape[0])) * 50
    dst_cols = src[:, 0] 
    dst_rows *= 1.
#    dst_rows += 1. * 50
    dst = np.vstack([dst_cols, dst_rows]).T
    
    # find the indices in the warping map

    idx = range(4)
    for i, (x, y) in enumerate (zip (index_x, index_y)):
        idx[i] = find_map_index(x,y, 50, 50 )
 
                   
    #---put label positions after transform               
    u0 = dst[idx[0], :]
    u1 = dst[idx[1], :]
    u2 = dst[idx[2], :]
    u3 = dst[idx[3], :]
    #---
    dst_label = np.vstack((u0, u1, u2, u3))
    print dst_label
    
    #left bound
    left = min(u0[0], u3[0])
    #right bound
    right = max(u1[0], u2[0])
    #top bound
    top = min(u0[1], u1[1])
    #bottom bound
    bottom = max(u2[1], u3[1])
       
    tform = PiecewiseAffineTransform()
    tform.estimate(src, dst)
  #%%  
    out_rows = image.shape[0] + 50#- 1.5 * 50
    out_cols = cols
    out = warp(image, tform.inverse, output_shape=(rows + 100, cols))


    fig, ax = plt.subplots()
    ax.imshow(image)
    ax.plot(dst_label[ :, 1], dst_label[ :, 0],'g*')
    ax.plot(tform(src)[:, 0], tform(src)[:, 1], '.b')

#    ax.plot([left, right], [top, bottom], 'r.')
    ax.plot(ori_labely, ori_labelx,'bo')
    ax.axis((0, out_cols, out_rows, 0))
    plt.show()

#%%

    
    fig, ax = plt.subplots()
    ax.imshow(out)
    ax.plot(dst_label[ :, 0],  dst_label[ :, 1],'g*')
    ax.plot(ori_labely, ori_labelx,'bo')

#    ax.plot(tform.inverse(src)[:, 0], tform.inverse(src)[:, 1], '.b')
    print left,right,top,bottom
    ax.axis((0, out_cols, out_rows+50, -50))
    plt.show()