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 flexible 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("munterfinger/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 reflect the arguments and return values of their counterparts (hf::encode_polyline and hf::decode_polyline):

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
)

encode(line)

decode("BlBoz5xJ67i1BU1B7PUzIhaUxL7YU")


## 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")

encode_sf(sfg)

decode_sf("BlBoz5xJ67i1BU1B7PUzIhaUxL7YU")