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https://github.com/hunzikp/BoostLines

Fast geometric line operations in R
https://github.com/hunzikp/BoostLines

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Fast geometric line operations in R

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README 

        
---

title: "BoostLines package"

author: "Philipp Hunziker"

date: "Feburary 15, 2018"

output: github_document

---



```{r setup, include=FALSE}

knitr::opts_chunk$set(echo = TRUE)

```



Fast geometric operations on lines using [Boost Geometries](http://www.boost.org/doc/libs/1_65_1/libs/geometry/doc/html/index.html); primarily for work on planar networks.



CAUTION: This package is in development - its interface may change.



## Installation



You can install the package directly from this repository:



```{r eval=FALSE}

library(devtools)

install_github("hunzikp/BoostLines")

```



## Usage



### Overview



* [Cast as/from `SpatialLines`](#cast-to-and-from-spatiallines-objects)

* [Noding](#noding)

* [Intersection](#intersection)

* [Minimal distance](#minimal-distance)

* [Create line grid](#create-line-grid)

* [Concatenate](#concatenate-two-or-more-boostline-objects)

* [Elminiate multilines](#elminiate-multilines-in-spatiallines-objects)

* [Line lengths](#calculate-line-lengths)

* [Cast as `igraph`](#cast-as-igraph-object)

* [Split lines into shorter lines](#split-lines)



### Cast to and from `SpatialLines` objects



```{r boost}

library(BoostLines)

library(sp)



## Make some lines

set.seed(0)

N <- 250

lines.ls <- vector('list', N)

for (i in 1:N) {

  strt <- runif(1)

  range <- runif(1)

  coords <- matrix(runif(4, strt, strt+range), 2, 2)

  lines.ls[[i]] <- Lines(slinelist = list(Line(coords = coords)), ID = i)

}

test.sl <- SpatialLines(lines.ls)



## Make BoostLines object

test.bl <- BoostLines(test.sl)



## Cast back to SpatialLines

test_cast.sl <- unboost(test.bl) 

```



### Noding



```{r node}

## Node

out.ls <- bNode(test.bl)



## Unpack & plot result

noded.sl <- unboost(out.ls[[1]])

noded.ids <- out.ls[[2]]  # integer vector of original IDs

plot(noded.sl, col=sample(colors(), length(noded.sl), replace=TRUE))

```



### Intersection



```{r intersects}

## Intersect query

lmat <- bIntersects(test.bl)



## Compare with gIntersects

suppressMessages(library(rgeos))

lmat_geos <- gIntersects(test.sl, byid=TRUE)

all(lmat == lmat_geos)

```



### Minimal distance



```{r distance}

## Calc Distances

dmat <- bDistance(test.bl)



## Compare with gDistance

dmat_geos <- gDistance(test.sl, byid=TRUE)

summary(abs(as.vector(dmat - dmat_geos)))

```



### Create line grid



```{r grid}

## Create a RasterLayer

library(raster)

set.seed(0)

ras <- raster(matrix(rnorm(20^2), 20, 20))



## Create a gridded, 8-connected BoostLines object

grid.bl <- bGrid(ras, n8 = TRUE)



## Plot raster & gridded lines

grid.sl <- unboost(grid.bl)

plot(ras)

plot(grid.sl, add=TRUE)

```



### Concatenate two or more BoostLine objects



```{r concat}

## Create two BoostLine Objects

grid1.bl <- bGrid(x = c(0,0), nrow = 10, ncol = 10, res = 1, n8 = FALSE)

grid2.bl <- bGrid(x = c(0.5,0.5), nrow = 10, ncol = 10, res = 1, n8 = FALSE)



## Concatenate

app.bl <- bAppend(list(grid1.bl, grid2.bl))



## Plot joint BoostLine object

app.sl <- unboost(app.bl)

plot(app.sl)

```



Note: `bAppend` does not node lines. For noding, use `bNode`.



### Elminiate multilines in SpatialLines* objects



The `BoostLines` function only accepts `SpatialLine*` objects without multilines. I.e. each feature must be a simple line string. The `remove_multilines` function removes multiline features in `SpatialLine*` objects and replaces them with simple lines.



```{r multiline}

## Create a SpatialLines object containing a multiline

set.seed(0)

eLine1 <- Line(matrix(rnorm(4), 2, 2))

eLine2 <- Line(matrix(rnorm(4), 2, 2))

eLines <- Lines(slinelist = list(eLine1, eLine2), '1')

sl <- SpatialLines(list(eLines))



## Try to cast as BoostLines object

library(testthat)

expect_error(BoostLines(sl))



## Remove Multilines

sl2 <- remove_multilines(sl)



## Try again

bl <- BoostLines(sl2)

```



### Calculate line lengths



```{r length}

## Create a BoostLines object

ras <- raster(matrix(rnorm(20^2), 20, 20))

bl <- bGrid(ras)



## Calculate lengths

lengths <- bLength(bl, lonlat = FALSE) ## If lonlat=TRUE, lengths are returned in meters

summary(lengths)



```



### Cast as `igraph` object



```{r igraph}

## Create a BoostLines object

ras <- raster(matrix(rnorm(20^2), 20, 20))

bl <- bGrid(ras)



## Cast as igraph object

df <- data.frame(edge_id = 1:length(bl))

suppressMessages(library(igraph))

gr <- boost2graph(x = bl, df = df, lonlat = FALSE, plot.result = TRUE)



## Explore vertex and edge attributes

print(vertex_attr_names(gr))

print(edge_attr_names(gr))



```



### Split lines



```{r split}

## Split

out.ls <- bSplit(test.bl, maxlen = 0.05)



## Summary of line lengths

split.bl <- out.ls[[1]]

split.ids <- out.ls[[2]]  # integer vector of original IDs

summary(bLength(split.bl, lonlat = FALSE))

```