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In flexpolyline: Flexible Polyline Encoding

knitr::opts_chunk$set(
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The flexpolyline R package provides a binding to the C++ implementation of the flexible polyline encoding by HERE. The flexible polyline encoding is a lossy compressed representation of a list of coordinate pairs or coordinate triples.

The encoding is achieved by:

(1) Reducing the decimal digits of each value; (2) encoding only the offset from the previous point; (3) using variable length for each coordinate delta; and (4) using 64 URL-safe characters to display the result. The felxible polyline encoding is a variant of the Encoded Polyline Algorithm Format by Google.

Note:

• Decoding gives reliable results up to a precision of 7 digits. The tests are also limited to this range.
• The order of the coordinates (lng, lat) does not correspond to the original C++ implementation (lat, lng). This enables simple conversion to sf objects, without reordering the columns.
• The encoding is lossy, this means the encoding process could reduce the precision of your data.

Installation

You can install the released version of flexpolyline from CRAN with:

install.packages("flexpolyline")

Install the development version from GitHub with:

remotes::install_github("munterfi/flexpolyline")

C++ binding

Encoding and decoding in R is straight forward by using encode() and decode(). These functions are binding to the flexpolyline C++ implementation and have similar arguments and return values as their counterparts (hf::encode_polyline and hf::decode_polyline):

library(flexpolyline)

(line <- matrix(
  c(8.69821, 50.10228, 10,
    8.69567, 50.10201, 20,
    8.69150, 50.10063, 30,
    8.68752, 50.09878, 40),
  ncol = 3, byrow = TRUE
))

(encoded <- encode(line))

(decoded <- decode(encoded))

Simple feature support

A common way to deal with spatial data in R is the sf package, which is built on the concept of simple features. The functions encode_sf() and decode_sf() provide an interface that support the encoding of sf objects:

(sfg <- sf::st_linestring(line, dim = "XYZ"))

(encoded <- encode_sf(sfg))

(decoded <- decode_sf(encoded))

References

• Flexible Polyline Encoding by HERE
• Encoded Polyline Algorithm Format
• Simple Features for R
• Inspired by the googlePolylines package

flexpolyline documentation built on Feb. 16, 2023, 7:42 p.m.