Decode Polyline

Description

Decodes encoded polylines into a list of data.frames.

Usage

decode(polylines)

Arguments

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

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

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

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

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

Value

list of sf attributes

WKT Polyline

Description

Converts well-known text into encoded polylines.

Usage

wkt_polyline(obj)

Arguments

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)