I was looking for a way to extract points from 4 graphs i have plotted in Python in order to run the Ramer Douglas peucker algorithm on the points. Ideally the data would be presented in a series of x and y co-ordinates as the current data set is presented differently. Each graph is made up of around 2000 points but they are not formatted as X and Y co-ordinates in the data set. I have attached the code used to plot the graphs as well as the data set if anyone has any suggestions.
Cheers!!
Inserting the line of code plt.gca().lines[-1].get_xydata() (right below the line where you create a plot: plt.plot(distances, alts, color='blue')) will allow you to extract the x-y coordinates for all points of each line you plot.
I then created an empty list, line_coords, to store the x-y coordinates for each of the four lines, and then iterated over each of these four sets of coordinates with the RDP algorithm:
rdp_res = []
for line in line_coords:
rdp_res.append(rdp(line))
The list rdp_res contains the RDP algorithm's output for each of the four lines:
[array([[4.92025194e+00, 3.80000000e+01],
[5.24522347e+01, 3.80000000e+01],
[8.59726863e+01, 3.77000000e+01],
...,
[3.07740662e+04, 3.60000000e+01],
[3.08035662e+04, 3.60000000e+01],
[3.08075068e+04, 3.59000000e+01]]),
array([[4.92025194e+00, 3.80000000e+01],
[5.24522347e+01, 3.80000000e+01],
[8.59726863e+01, 3.77000000e+01],
...,
[2.81487733e+04, 5.20000000e+01],
[2.81536662e+04, 5.18000000e+01],
[2.82000946e+04, 5.18000000e+01]]),
array([[4.92025194e+00, 3.80000000e+01],
[5.24522347e+01, 3.80000000e+01],
[8.59726863e+01, 3.77000000e+01],
...,
[2.37758154e+04, 1.26000000e+01],
[2.37973123e+04, 1.30000000e+01],
[2.38301772e+04, 1.38000000e+01]]),
array([[4.92025194e+00, 3.80000000e+01],
[5.24522347e+01, 3.80000000e+01],
[8.59726863e+01, 3.77000000e+01],
...,
[2.59717233e+04, 1.83600000e+02],
[2.60321544e+04, 1.83400000e+02],
[2.60884831e+04, 1.83400000e+02]])]
We can compare the number of coordinates in each line:
line_coords[0].shape, line_coords[1].shape, line_coords[2].shape, line_coords[3].shape
((1167, 2), (2133, 2), (2869, 2), (3597, 2))
With the number of coordinates remaining after running RDP on each line:
rdp_res[0].shape, rdp_res[1].shape, rdp_res[2].shape, rdp_res[3].shape
((1080, 2), (1947, 2), (2643, 2), (3360, 2))
Below I've pasted in your original code with all of my modifications included:
"""
File for importing route data from a json file
"""
import json
import os
import matplotlib.pyplot as plt
from rdp import rdp
import numpy as np
def get_data(file_name):
"""
method to retrieve JSON data from "file"
:param file_name: string representing file in which JSON data is stored
:return data: Pyhonic data created from JSON file information
"""
with open(os.path.join(os.sys.path[0], file_name), "r") as data_file:
data = json.load(data_file) # load data from JSON file
return data
if __name__== "__main__":
file_name = 'json_data.json'
routes = get_data(file_name)
print("Total Time")
print(routes[0]["totalTime"])
print("Total Distance")
print(routes[0]["totalDistance"])
routesPos = 0
edgePos = 0
edgeDistance = 0
alts = []
distances = []
line_coords = []
while routesPos < len(routes):
while edgePos < len(routes[routesPos]["edges"]):
edgeDistance = edgeDistance + routes[routesPos]["edges"][edgePos]["edgeDistance"]
distances.append(edgeDistance)
alts.append(routes[routesPos]["edges"][edgePos]["endLocation"]["alt"])
edgePos += 1
plt.plot(distances, alts, color='blue')
coords = plt.gca().lines[-1].get_xydata() # Get coords for most recently plotted line
line_coords.append(coords)
edgeDistance = 0
routesPos += 1
edgePos = 0
rdp_res = []
for line in line_coords:
rdp_res.append(rdp(line))
line_coords list. For example, if you want to see the points in the first line, you could just run line_coords[0] to see a list of all x-y coords in that line.