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geojson operations
Scott Chamberlain and Jeroen Ooms
2024-08-30
Source:vignettes/geojson-operations.Rmd
geojson-operations.Rmd
The geojson
package has functions to do basic operations
on GeoJSON classes.
First, let’s make a GeoJSON object
x <- '{
"type": "GeometryCollection",
"geometries": [
{
"type": "Point",
"coordinates": [100.0, 0.0]
},
{
"type": "LineString",
"coordinates": [ [101.0, 0.0], [102.0, 1.0] ]
}
]
}'
(y <- geometrycollection(x))
#> <GeometryCollection>
#> geometries (n): 2
#> geometries (geometry / length):
#> Point / 2
#> LineString / 2
inspect the object
Get the string
y[[1]]
#> [1] "{\n \"type\": \"GeometryCollection\",\n \"geometries\": [\n {\n \"type\": \"Point\",\n \"coordinates\": [100.0, 0.0]\n },\n {\n \"type\": \"LineString\",\n \"coordinates\": [ [101.0, 0.0], [102.0, 1.0] ]\n }\n ]\n}"
Get the type
geo_type(y)
#> [1] "GeometryCollection"
Pretty print the geojson
geo_pretty(y)
#> {
#> "type": "GeometryCollection",
#> "geometries": [
#> {
#> "type": "Point",
#> "coordinates": [
#> 100.0,
#> 0.0
#> ]
#> },
#> {
#> "type": "LineString",
#> "coordinates": [
#> [
#> 101.0,
#> 0.0
#> ],
#> [
#> 102.0,
#> 1.0
#> ]
#> ]
#> }
#> ]
#> }
#>
Write to disk
geo_write(y, f <- tempfile(fileext = ".geojson"))
jsonlite::fromJSON(f, FALSE)
#> $type
#> [1] "GeometryCollection"
#>
#> $geometries
#> $geometries[[1]]
#> $geometries[[1]]$type
#> [1] "Point"
#>
#> $geometries[[1]]$coordinates
#> $geometries[[1]]$coordinates[[1]]
#> [1] 100
#>
#> $geometries[[1]]$coordinates[[2]]
#> [1] 0
#>
#>
#>
#> $geometries[[2]]
#> $geometries[[2]]$type
#> [1] "LineString"
#>
#> $geometries[[2]]$coordinates
#> $geometries[[2]]$coordinates[[1]]
#> $geometries[[2]]$coordinates[[1]][[1]]
#> [1] 101
#>
#> $geometries[[2]]$coordinates[[1]][[2]]
#> [1] 0
#>
#>
#> $geometries[[2]]$coordinates[[2]]
#> $geometries[[2]]$coordinates[[2]][[1]]
#> [1] 102
#>
#> $geometries[[2]]$coordinates[[2]][[2]]
#> [1] 1
properties
Add properties
x <- '{ "type": "LineString", "coordinates": [ [100.0, 0.0], [101.0, 1.0] ]}'
res <- linestring(x) %>% feature() %>% properties_add(population = 1000)
res
#> <Feature>
#> type: LineString
#> coordinates: [[100.0,0.0],[101.0,1.0]]
Get a property
properties_get(res, property = 'population')
#> 1000
crs
Add crs
crs <- '{
"type": "name",
"properties": {
"name": "urn:ogc:def:crs:OGC:1.3:CRS84"
}
}'
z <- x %>% feature() %>% crs_add(crs)
z
#> {
#> "type": "Feature",
#> "properties": {
#>
#> },
#> "geometry": {
#> "type": "LineString",
#> "coordinates": [
#> [
#> 100.0,
#> 0.0
#> ],
#> [
#> 101.0,
#> 1.0
#> ]
#> ]
#> },
#> "crs": {
#> "type": "name",
#> "properties": {
#> "name": "urn:ogc:def:crs:OGC:1.3:CRS84"
#> }
#> }
#> }
Get crs
crs_get(z)
#> $type
#> [1] "name"
#>
#> $properties
#> $properties$name
#> [1] "urn:ogc:def:crs:OGC:1.3:CRS84"
bbox
Add bbox - by default, if you don’t pass a bbox into
bbox_add()
we attempt to calculate the bbox for you. You
can also pass in your own bbox.
tt <- x %>% feature() %>% bbox_add()
tt
#> {
#> "type": "Feature",
#> "properties": {
#>
#> },
#> "geometry": {
#> "type": "LineString",
#> "coordinates": [
#> [
#> 100.0,
#> 0.0
#> ],
#> [
#> 101.0,
#> 1.0
#> ]
#> ]
#> },
#> "bbox": [
#> 100,
#> 0,
#> 101,
#> 1
#> ]
#> }
Get bbox
bbox_get(tt)
#> [1] 100 0 101 1
geojson in data.frame’s
It’s really easy to put geojson
class objects into
data.frame’s as well.
The ideal solution is to put them into tbl
’s (see the
tibble
package)
Make a point
x <- '{ "type": "Point", "coordinates": [100.0, 0.0] }'
(pt <- point(x))
#> <Point>
#> coordinates: [100.0,0.0]
Put the point into a tbl
library("tibble")
data_frame(a = 1:5, b = list(pt))
#> # A tibble: 5 × 2
#> a b
#> <int> <list>
#> 1 1 <geopoint [1]>
#> 2 2 <geopoint [1]>
#> 3 3 <geopoint [1]>
#> 4 4 <geopoint [1]>
#> 5 5 <geopoint [1]>
Another object, here a multilinestring
x <- '{ "type": "MultiLineString",
"coordinates": [ [ [100.0, 0.0], [101.0, 1.0] ], [ [102.0, 2.0], [103.0, 3.0] ] ] }'
(mls <- multilinestring(x))
#> <MultiLineString>
#> no. lines: 2
#> no. nodes / line: 2, 2
#> coordinates: [[[100.0,0.0],[101.0,1.0]],[[102.0,2.0],[103.0,3.0]]]
Put into a tbl
data_frame(a = 1:5, b = list(mls))
#> # A tibble: 5 × 2
#> a b
#> <int> <list>
#> 1 1 <gmltlnst [1]>
#> 2 2 <gmltlnst [1]>
#> 3 3 <gmltlnst [1]>
#> 4 4 <gmltlnst [1]>
#> 5 5 <gmltlnst [1]>
Put the point
and multilinestring
into the
same tbl
(df <- data_frame(a = 1:5, b = list(pt), c = list(mls)))
#> # A tibble: 5 × 3
#> a b c
#> <int> <list> <list>
#> 1 1 <geopoint [1]> <gmltlnst [1]>
#> 2 2 <geopoint [1]> <gmltlnst [1]>
#> 3 3 <geopoint [1]> <gmltlnst [1]>
#> 4 4 <geopoint [1]> <gmltlnst [1]>
#> 5 5 <geopoint [1]> <gmltlnst [1]>
And you can pull the geojson back out
df$b
#> [[1]]
#> <Point>
#> coordinates: [100.0,0.0]
#>
#> [[2]]
#> <Point>
#> coordinates: [100.0,0.0]
#>
#> [[3]]
#> <Point>
#> coordinates: [100.0,0.0]
#>
#> [[4]]
#> <Point>
#> coordinates: [100.0,0.0]
#>
#> [[5]]
#> <Point>
#> coordinates: [100.0,0.0]
df$b[[1]]
#> <Point>
#> coordinates: [100.0,0.0]