WFS_getfeature: Retrieve WFS information with the GetFeature request

In HanOostdijk/HOQCwfs: Web Feature Service (WFS) read-only interface

Retrieve WFS information with the GetFeature request

Description

Retrieving the requested geospatial data will most often be done by specifying the bounding box of the region of interest or by specifying a filter to restrict the features that will be returned. As described in https://docs.geoserver.org/latest/en/user/filter/syntax.html there are two ways to specify a filter: with the cql_filter or the filter argument. See Details .

Usage

WFS_getfeature(
  typename,
  ...,
  httrType = c("GET", "POST"),
  url = WFS_get_url(),
  version = WFS_get_version(),
  debug = F,
  to_sf = T,
  sfverbose = F,
  echo_request = F,
  httrverbose = rep(F, 4)
)

Arguments

typename	Character string with the name of a feature (such as e.g. found by using WFS_featuretypes() )
...	optional arguments for the GetFeature request. See Details
httrType	Character string with the type of httr request: GET or POST
url	URL of the WFS service. See WFS_get_url() for the default
version	software version for WFS service request. See WFS_get_version() for the default
debug	Logical indicating the httr response is to be returned
to_sf	Logical indicating if a json object should be converted to an sf object
sfverbose	Logical indicating if sf::read_sf() messages will be displayed
echo_request	Logical indicating if the generated GET or POST request is to be echoed
httrverbose	Logical vector of up to four entries to be used in httr::verbose()

Details

Arguments that are recognized by the GetFeature request are:

• bbox (not in combination with cql_filter or filter)

• cql_filter a filter derived from the plain-text language mechanism for the OGC Catalog specification. See for an introduction the tutorial in the GeoServer webpages. Also see the Examples

• filter an XML-based specification of a filter. See this GeoServer page and the Examples.
  And see wfsfilteraux for functions to build these XML filters

• resultType - default 'results' and alternative 'hits'. In the latter case only the number of matched features (numbeOfFeatures in 1.1.0 or numberMatched in 2.0.0) is returned

• srsname indicate the crs for the coordinates of the output e.g. srsname='EPSG:4326'

• propertyname the name of the fields to retrieve. The id and geometry fields will always be included

• startIndex number of features to skip before retrieving features ( the output with startindex=1 will start with the second feature )

• maxfeatures (version 1.1.0) or count (version 2.0.0) indicates the number of features to retrieve. When the wrong argument is specified it will be translated in the other. The GetFeature argument outputFormat has value 'application/json' but this can be overwritten

See vignette for more examples

Value

a sf object with the requested information (the 'id' variable and the geometry will always be included) or a character string with an error message

Examples

## Not run: 
# examples use the default dataset !
# retrieve all fields from the first 5 features of "topp:gidw_groenbomen" :
wfs1     <-  WFS_getfeature("topp:gidw_groenbomen", maxfeatures=5)

# retrieve all fields from all features of "topp:gidw_groenbomen" in the indicated bbox :
bbox_wgs84 <- "4.860793, 52.313319, 4.861587, 52.316493,EPSG:4326"
wfs2     <-  WFS_getfeature("topp:gidw_groenbomen", bbox=bbox_wgs84)

# retrieve all fields from all features of "topp:gidw_groenbomen" in the indicated bbox
# coordinates in bbox given in same crs as the data (EPSG:28992) but we want the output coordinates in WGS84 :
bbox_28992 <- "119103.4, 480726.0, 119160.1, 481078.7"
wfs3     <-  WFS_getfeature("topp:gidw_groenbomen", bbox=bbox_28992,srsname='EPSG:4326' )

# filter species with embedded quote (using cql_filter=) :
a_species    <- r"(Prunus serrulata 'Kanzan')"    # embedded quote
bm=stringr::str_replace_all(a_species,"'","''")   # double that for cql_filter
wfs4     <-  WFS_getfeature("topp:gidw_groenbomen",
           cql_filter= glue::glue("boom_omschrijf='{bm}'") )

# filter species with embedded quote (using filter=) and two of the auxiliary functions :
f5   <- build_filter(version='1.1.0' ,
           propeq_xml('topp:boom_omschrijf',a_tree)
    )
wfs5 <- WFS_getfeature("topp:gidw_groenbomen", version='1.1.0',
           filter  = f5)

## End(Not run)

HanOostdijk/HOQCwfs documentation built on March 6, 2023, 8:18 a.m.