Package 'googlePolylines'

Decode Polyline

Description

Decodes encoded polylines into a list of data.frames.

Usage

decode(polylines)

Arguments

polylines

vector of encoded polyline strings

Examples

polylines <- c(
  "ohlbDnbmhN~suq@am{tAw`qsAeyhGvkz`@fge}A",
  "ggmnDt}wmLgc`DesuQvvrLofdDorqGtzzV"
)

decode(polylines)

---

Encode

Description

Encodes coordinates into an encoded polyline.

Usage

encode(obj, ...)

## S3 method for class 'sf'
encode(obj, strip = FALSE, ...)

## S3 method for class 'data.frame'
encode(obj, lon = NULL, lat = NULL, byrow = FALSE, ...)

Arguments

obj	either an sf object or data.frame
...	other parameters passed to methods
strip	logical indicating if sf attributes should be stripped. Useful if you want to reduce the size even further, but you will lose the spatial attributes associated with the sf object
lon	vector of longitudes
lat	vector of latitudes
byrow	logical indicating if the encoding should be done for each row

Details

The function assumes Google Web Mercator projection (WSG 84 / EPSG:3857 / EPSG:900913) for inputs and outputs.

Will work with

• sf and sfc objects directly

• data.frames - It will attempt to find lat & lon coordinates, or you can explicitely define them using the lat and lon arguments

Value

sfencoded object

Note

When an sfencoded object is colulmn-subset using `[` and the encoded column is retained, the attributes of the column will remain. This is different behaviour to standard subsetting of data.frames, where all attributes are dropped by default. See examples.

When encoding an sf object, only the XY dimensions will be used, the Z or M (3D and/or Measure) dimensions are dropped.

See Also

encodeCoordinates

Examples

## data.frame
df <- data.frame(polygonId = c(1,1,1,1),
  lineId = c(1,1,1,1),
  lon = c(-80.190, -66.118, -64.757, -80.190),
  lat = c(26.774, 18.466, 32.321, 26.774))
  
## on a data.frame, it will attemp to find the lon & lat columns
encode(df)

## use byrow = TRUE to convert each row individually
encode(df, byrow = TRUE)


## Not run: 

## sf objects
library(sf)
nc <- sf::st_read(system.file("shape/nc.shp", package="sf"))

encoded <- encode(nc)

## view attributes
attributes(encoded) 

## view attributes of subset object
attributes(encoded[, c("AREA", "PERIMETER", "geometry")])

## view attributes without encoded column
attributes(encoded[, c("AREA", "PERIMETER")])

## strip attributes
encodedLite <- encode(nc, strip = TRUE)

attributes(encodedLite)

## view attributes of subset lite object
attributes(encodedLite[, c("AREA", "PERIMETER", "geometry")])

## view attributes without encoded column
attributes(encodedLite[, c("AREA", "PERIMETER")])

## End(Not run)

---

Encode coordinates

Description

Encodes a vector of lon & lat coordinates

Usage

encodeCoordinates(lon, lat)

Arguments

lon	vector of longitudes
lat	vector of latitudes

See Also

encode

Examples

## Not run: 

## Grouping by polygons and lines
df <- data.frame(polygonId = c(1,1,1,1,1,1,1,1,2,2,2,2),
  lineId = c(1,1,1,1,2,2,2,2,1,1,1,1),
  lon = c(-80.190, -66.118, -64.757, -80.190,  -70.579, -67.514, -66.668, -70.579, 
  -70, -49, -51, -70),
  lat = c(26.774, 18.466, 32.321, 26.774, 28.745, 29.570, 27.339, 28.745, 
  22, 23, 22, 22))


## using dplyr groups   

library(dplyr)
df %>%
  group_by(polygonId, lineId) %>% 
  summarise(polyline = encodeCoordinates(lon, lat))
  
## using data.table
library(data.table)
setDT(df)
df[, encodeCoordinates(lon = lon, lat = lat), by = .(polygonId, lineId)]



## End(Not run)

---

Geometry Row

Description

Extracts specific geometry rows of an sfencoded object

Usage

geometryRow(x, geometry = c("POINT", "LINESTRING", "POLYGON"), multi = TRUE)

Arguments

x	sfencoded object
geometry	the specific geometry to extract
multi	logical indicating if MULTI geometry objects are included

Value

the row indeces for the requested geometry

Examples

## Not run: 

df <- data.frame(myId = c(1,1,1,1,1,1,1,1,2,2,2,2),
	lineId = c(1,1,1,1,2,2,2,2,1,1,1,2),
	lon = c(-80.190,-66.118,-64.757,-80.190,-70.579,-67.514,-66.668,-70.579,-70,-49,-51,-70),
	lat = c(26.774, 18.466, 32.321, 26.774, 28.745, 29.570, 27.339, 28.745, 22, 23, 22, 22))

p1 <- as.matrix(df[1:4, c("lon", "lat")])
p2 <- as.matrix(df[5:8, c("lon", "lat")])
p3 <- as.matrix(df[9:12, c("lon", "lat")])

point <- sf::st_sfc(sf::st_point(x = c(df[1,"lon"], df[1,"lat"])))
multipoint <- sf::st_sfc(sf::st_multipoint(x = as.matrix(df[1:2, c("lon", "lat")])))
polygon <- sf::st_sfc(sf::st_polygon(x = list(p1, p2)))
linestring <- sf::st_sfc(sf::st_linestring(p3))
multilinestring <- sf::st_sfc(sf::st_multilinestring(list(p1, p2)))
multipolygon <- sf::st_sfc(sf::st_multipolygon(x = list(list(p1, p2), list(p3))))

sf <- rbind(
	st_sf(geo = polygon),
	st_sf(geo = multilinestring),
	st_sf(geo = linestring),
	st_sf(geo = point)
	)

encode(sf)

enc <- encode(sf)
geometryRow(enc, "POINT")
geometryRow(enc, "LINESTRING")
geometryRow(enc, "POLYGON")


## End(Not run)

---

Polyline WKT

Description

Converts encoded polylines into well-known text.

Usage

polyline_wkt(obj)

Arguments

obj	sfencoded object or encoded_column of encoded polylines

Details

'Polylines' refers to lat/lon coordinates encoded into strings using Google's polyline encoding algorithm.

The function assumes Google Web Mercator projection (WSG 84 / EPSG:3857 / EPSG:900913) for inputs and outputs.

Value

well-known text representation of the encoded polylines

Note

This will not work if you have specified strip = TRUE for encode()

Examples

## Not run: 

library(sf)
nc <- sf::st_read(system.file("shape/nc.shp", package="sf"))

## encode to polylines
enc <- encode(nc)

## convert encoded lines to well-known text
wkt <- polyline_wkt(enc)


## End(Not run)

---

sf Attributes

Description

Retrieves the sf attributes stored on the sfencoded object

Usage

sfAttributes(x)

Arguments

x	sfencoded object

Value

list of sf attributes

---

WKT Polyline

Description

Converts well-known text into encoded polylines.

Usage

wkt_polyline(obj)

Arguments

obj	sfencoded object or wkt_column of well-known text

Details

'Polylines' refers to lat/lon coordinates encoded into strings using Google's polyline encoding algorithm.

Value

encoded polyline representation of geometries

Examples

## Not run: 

library(sf)
nc <- sf::st_read(system.file("shape/nc.shp", package="sf"))

## encode to polylines
enc <- encode(nc)

## convert encoded lines to well-known text
wkt <- polyline_wkt(enc)

## convert well-known text back to polylines
enc2 <- wkt_polyline(wkt)


## End(Not run)

---