The package contains two Rcpp functions, which
bind directly to the C++ implementation of the flexible polyline
encoding. These functions target a tight interface from C++ to R and
reflect the arguments and return values of their counterparts
(`hf::encode_polyline`

and `hf::decode_polyline`

)
in the C++ implementation.

Encoding a line is straight forward by passing a matrix (column order
is longitude, latitude) with its coordinates to `encode()`

.
The default precision value is set to `5`

. If a matrix with
two columns is provided, the third dimension is automatically set to
`"ABSENT"`

:

```
library(flexpolyline)
<- matrix(
line2d c(8.69821, 50.10228,
8.69567, 50.10201,
8.69150, 50.10063,
8.68752, 50.09878),
ncol = 2, byrow = TRUE
)
<- encode(line2d, precision = 5))
(encodes2d #> [1] "BFoz5xJ67i1B1B7PzIhaxL7Y"
```

If a matrix with three columns is passed, a line with a third
dimension is encoded. The type of the third dimension can be passed to
the encoding and supports the following selection, that are specified
via an integer value via the `third_dim`

argument:

- 0: ABSENT
- 1: LEVEL
- 2: ALTITUDE
- 3: ELEVATION (default)
- 4: RESERVED1 (not available)
- 5: RESERVED2 (not available)
- 6: CUSTOM1
- 7: CUSTOM2

By default the precision of the third dimension
`third_dim_precision`

is set to the same value as the
precision value for the longitude and latitude dimensions.

```
<- matrix(
line3d c(8.69821, 50.10228, 10.11111,
8.69567, 50.10201, 20.22222,
8.69150, 50.10063, 30.33333,
8.68752, 50.09878, 40.44444),
ncol = 3, byrow = TRUE
)
<- encode(line3d, precision = 5, third_dim = 3, third_dim_precision = 5))
(encodes3d #> [1] "B1Voz5xJ67i1Bu629B1B7Pu629BzIhau629BxL7Yu629B"
```

In order to decode the lines from above, the encoded line string is
passed to the `decode()`

function. The function detects from
the encoded string if it is a two-dimensional or three-dimensional
line:

```
decode(encodes2d)
#> LNG LAT
#> [1,] 8.69821 50.10228
#> [2,] 8.69567 50.10201
#> [3,] 8.69150 50.10063
#> [4,] 8.68752 50.09878
```

In the case of a three-dimensional line, the third column is named
after the name of the third dimension that was chosen during the
encoding (in this example `"ELEVATION"`

):

```
decode(encodes3d)
#> LNG LAT ELEVATION
#> [1,] 8.69821 50.10228 10.11111
#> [2,] 8.69567 50.10201 20.22222
#> [3,] 8.69150 50.10063 30.33333
#> [4,] 8.68752 50.09878 40.44444
```

- Flexible Polyline Encoding by HERE
- Encoded Polyline Algorithm Format
- Inspired by the googlePolylines package