Loading the Spanish Cadastre INSPIRE WFS into a leaflet in R

Question

I am trying to load some WFS data into a leaflet using R. The problem is that there doesn't seem to be a straightforward way to collect it, unlike with WMS, which has the addWMSTiles() function in the leaflet package for R.

How can I proceed?

Out of all attempts so far, the one with "greatest" success (no success really, just fetched the XML data) was done using the following code:

library(c(XML,plyr))

fileurl <- "http://ovc.catastro.meh.es/INSPIRE/wfsCP.aspx?service=WFS&request=GetFeature&Typenames=cp.cadastralparcel&SRSname=EPSG::25830&bbox=233673,4015968,233761,4016008&version=2.0.0&"
doc <- xmlParse(fileurl,useInternalNodes = TRUE) ### xmlParse()- is to parse the xml content, the parsed content is stored into doc
xL <- xmlToList(doc) ###is to convert xml doc into List

data <- ldply(xL, data.frame)
head(data)

This yields an XML with polygon points in one of the columns, but how can I include this in a Leaflet? It seems too much of a workaround to do this in this way. Does anyone know how to do this in a more straightforward manner?

Link to the inspire XML document on how to request data

UPDATE 1: I have found a way to do this using the sf R package. With

st_read("http://ovc.catastro.meh.es/INSPIRE/wfsCP.aspx?service=WFS&request=GetFeature&Typenames=cp.cadastralparcel&SRSname=EPSG::25830&bbox=233673,4015968,233761,4016008&version=2.0.0&")

Unfortunately it was not as straightforward as it seems. I had to install OSGeo4W64 in my machine because the rgdal package was not working properly. I also had to make the evironment variables point toward the OSGeo4W64, and delete the ones that pointed to sf. I followed this guide.

However I am still wondering how to integrate this in R just as I did with WMS. As you may notice from the url in st_read, it includes a Bounding Box, which I want leaflet to determine just like it did with WMS (which also required one)

Answer 1

If you want to load WFS data in leaflet, you can follow these steps:

1. Download WFS data in R (with sf)
2. Transform data to WGS84 datum (if needed)

3. Visualise in Leaflet

   # load libraries
   library(sf)
   library(leaflet)
   
   # 1. read WFS data
   data_sf <- st_read("http://ovc.catastro.meh.es/INSPIRE/wfsCP.aspx?service=WFS&request=GetFeature&Typenames=cp.cadastralparcel&SRSname=EPSG::25830&bbox=233673,4015968,233761,4016008&version=2.0.0&")
   
   # 2. transform to WGS84
   data_sf_wgs84 <- st_transform(data_sf,4326)
   
   # 3. load data in leaflet
   leaflet() %>%
     addTiles() %>%
     addPolygons(data = data_sf_wgs84)
   

You can also customize the appearance, fill color,...
See https://rstudio.github.io/leaflet/ for more info and examples

    # with some additional options:
    leaflet() %>%
      addTiles() %>%
      addPolygons(data = data_sf_wgs84,
          color = 'black',
          fillOpacity = 1.0,
          fillColor = ~colorQuantile("viridis", areaValue)(areaValue),
          popup = ~nationalCadastralReference)

Answer 2

You probably won't be able to do it directly, because most clients can't handle the output of complex feature WFS such as this one.

We can see the output is a complex feature WFS by doing a DescribeFeatureType operation like:

http://ovc.catastro.meh.es/INSPIRE/wfsCP.aspx?service=WFS&request=DescribeFeatureType&Typenames=cp.cadastralparcel&version=2.0.0&

And looking at the result:

http://inspire.ec.europa.eu/schemas/cp/4.0/CadastralParcels.xsd