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Decoding the shape of the route as a flexible-polyline returned in Routing API v8 by python

Last Updated: November 2022
Product: HERE Routing API v8
Audience: External developers
Article Type: How-to / Technical Guide

Overview

In HERE Routing API v8, the route geometry is not returned as a list of coordinates. Instead, the route shape is provided as an encoded string using the Flexible Polyline format.

This article explains:

  • What a flexible polyline is
  • Where to find it in a Routing API v8 response
  • How to decode it using Python

What Is a Flexible Polyline?

A flexible polyline is a compact string representation of a sequence of geographic coordinates (and optionally relative heights).
It significantly reduces payload size compared to raw coordinate arrays.

The Routing API v8 returns this encoded polyline in the polyline field of each route section.

Prerequisites

Before proceeding, ensure the following:

  • A valid HERE API key
  • Python 3.x
pip install requests flexpolyline

Example: Calling Routing API v8 and Decoding the Polyline

The following Python example demonstrates:

  • Calling the Routing API v8
  • Extracting the polyline from the response
  • Decoding it into latitude/longitude coordinates

Step 1: Import Required Libraries

import requests

import json

import flexpolyline as fp

Step 2: Define Parameters

apikey = 'YOUR_API_KEY'

origin_point = '43.435236,-80.444766'

destination_point = '43.41117,-80.4937'

via_point = '43.41517,-80.5917'

Step 3: Call the Routing API v8

url = 'https://router.hereapi.com/v8/routes'

headers = {'Content-Type': 'application/json'}

params = {

'origin': origin_point,

'destination': destination_point,

'via': via_point,

'transportMode': 'car',

'return': 'summary,polyline,travelSummary,instructions,actions,elevation',

'spans': 'names,speedLimit,carAttributes',

'apikey': apikey

}

response = requests.get(url, params=params, headers=headers)

print('HTTP Status Code:', response.status_code)

Step 4: Parse the Response and Extract the Polyline

output = json.loads(response.text)

# Retrieve the encoded flexible polyline

polyline = output["routes"][0]["sections"][0]["polyline"]

print('Response Language:',

output["routes"][0]["sections"][0]["language"])

print('Encoded Flexible Polyline:')

print(polyline)

Step 5: Decode the Flexible Polyline

decoded_coordinates = fp.dict_decode(polyline)

for index, coordinate in enumerate(decoded_coordinates, start=1):

print(f'Decoded waypoint #{index}: {coordinate}')

Each decoded waypoint is returned as a dictionary containing latitude and longitude values.

Result

After decoding, the flexible polyline is converted into a list of geographic coordinates, which can be:

  • Rendered on a map
  • Exported to GeoJSON
  • Used for spatial analysis or visualization

Related Links

  • HERE Flexible Polyline GitHub Repository
  • HERE Routing API v8 Documentation

Notes

  • Each route may contain multiple sections, each with its own polyline.
  • Always decode the correct sections[n].polyline entry for the part of the route you need.