library(VicmapR)
library(sf)
library(leaflet)
#check sf installation
::sf_extSoftVersion() sf
In order to begin a query of the WFS server a spatial layer must be selected. To know which layers are available use the listLayers()
function, which will return ~ 690 layers to choose from.
<- listLayers()
available_layers
head(available_layers, 10)
VicmapR introduces a new class called vicmap_promise
, which is an extension to the httr::url
class. Essentially this object is how the vicmap query is stored before data is collected. That is to say vicmap_promise
is essentially a promise of what data will be retrieved.
In order to generate a new promise the vicmap_query
function can be used to select the layer. The promise prints a sample of the data (max = 6 rows) as well as the dimensions (nrow and ncol).
# query the watercourse layer
vicmap_query(layer = "datavic:VMHYDRO_WATERCOURSE_DRAIN")
The vicmap_promise
object can be easily added to through piping in of additional functions (e.g. head()
, filter()
and select()
).
The resulting query can be displayed using the show_query()
function, which will list the WFS parameters.
vicmap_query(layer = "datavic:VMHYDRO_WATERCOURSE_DRAIN") %>%
head(50) %>% #return only 50 rows
filter(HIERARCHY == "L") %>% # filter the column 'HIERACHY' to values of 'L'
select(HIERARCHY, PFI) %>% # select columns 'HIERARCHY' and 'PFI'
show_query()
In order to return a spatial data.frame object (sf
) collect()
must be used.
<- vicmap_query(layer = "datavic:VMHYDRO_WATERCOURSE_DRAIN") %>%
watercourse_data head(50) %>% #return only 50 rows
filter(HIERARCHY == "L") %>% # filter the column 'HIERACHY' to values of 'L'
select(HIERARCHY, PFI) %>% # select columns 'HIERARCHY' and 'PFI'
collect()
str(watercourse_data)
VicmapR translates numerous geometric filter functions available in the Victorian Government’s WFS Geoserver supports numerous geometric filters:
EQUALS
DISJOINT
INTERSECTS
TOUCHES
CROSSES
WITHIN
CONTAINS
OVERLAPS
DWITHIN
BEYOND
BBOX
These filters can be used within the filter()
function by providing them an object of class sf/sfc/sfg/bbox
. Below is a leaflet map with the melbourne rail network being read in with the use of three different types of filter functions: INTERSECTS()
, BBOX()
and DWITHIN()
.
#### Return objects that intersect melbourne ####
# Read in an example shape to restrict our query to using geometric filtering
<- sf::st_read(system.file("shapes/melbourne.geojson", package="VicmapR"), quiet = F) %>%
melbourne ::st_transform(4283)
sf
# Return data that intersects melbourne
<- vicmap_query(layer = "datavic:VMTRANS_TR_RAIL") %>% # layer to query
rail_intersects filter(INTERSECTS(melbourne)) %>% # more advanced geometric filter
collect()
<- vicmap_query(layer = "datavic:VMTRANS_TR_RAIL") %>%
rail_bbox filter(BBOX(sf::st_bbox(melbourne))) %>%
collect()
<- vicmap_query(layer = "datavic:VMTRANS_TR_RAIL") %>%
rail_dwithin filter(DWITHIN(melbourne %>% sf::st_centroid(), distance = 10000, units = "meters")) %>%
collect()
leaflet(width = "100%") %>%
addProviderTiles("CartoDB.Positron") %>%
addPolygons(data = melbourne, color = "grey", group = "Melbourne polygon") %>%
addPolygons(data = sf::st_bbox(melbourne) %>% st_as_sfc(), color = "black", group = "Melbourne bbox") %>%
addPolylines(data = rail_intersects, color = "Red", group = "INTERSECTS") %>%
addPolylines(data = rail_bbox, color = "Blue", group = "BBOX") %>%
addPolylines(data = rail_dwithin, color = "Green", group = "DWITHIN") %>%
addLayersControl(baseGroups = c("Melbourne polygon", "Melbourne bbox"),
overlayGroups = c("INTERSECTS", "BBOX", "DWITHIN")) %>%
hideGroup(c("BBOX", "DWITHIN"))