Export Data Table to Google Maps KML in R

Question

Exporting a KML to use in Google Maps. Here is the code to export (adapted from here):

t_expkml_c <- function(obj, archivo,
                     col_nombre, col_desc, col_color,
                     mapa_colores = "mapa_colores_topaz",
                     mapa_nombre = "Mapa_TSE", mapa_desc = "Mapa Creado por PE de TSE") {
  
  # - changes projection
  if (proj4string(obj)!="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0") {
    cat("Input SpatialPolygonsDataFrame ",obj," re-projected from ",
        proj4string(obj)," to WGS84 longlat\n",sep="")
    assign(obj,spTransform(obj,CRS(" +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0")))
  } # check projection
  
  # opens file
  kmlFile <- file(archivo,
                  open = "w")
  
  # goes through each polygon
  # usa maptools::kmlPolygon
  Xout <- sapply(slot(obj,
                      "polygons"),
                 function(x) {
                   maptools::kmlPolygon(x, # Object 
                                        name = as(obj, "data.frame")[slot(x, "ID"), col_nombre],
                                        # name column
                                        col = mapa_colores[as.numeric(as(obj, "data.frame")[slot(x, "ID"), col_color])],
                                        # color column
                                        lwd = 0.5, # stroke
                                        border = NA, # borders
                                        visibility = TRUE, 
                                        description = as(obj,"data.frame")[slot(x, "ID"), col_desc], #description (what I need to change)
                   )
                 }
  )
  
  # export polyon out
  cat(kmlPolygon(kmlname=mapa_nombre,
                 kmldescription=mapa_desc)$header,
      file = kmlFile, sep="\n")
  # estilos
  cat(unlist(Xout["style",]),
      file = kmlFile, sep="\n")
  # contenidos
  cat(unlist(Xout["content",]),
      file = kmlFile, sep="\n")
  # footers
  cat(kmlPolygon()$footer,
      file = kmlFile, sep="\n")
  close(kmlFile) # end
}

This works okay when I have only one column from the kmlmap@data data.frame (the object is class SpatialPolygonsDataFrame). However, I want to export a larger data table, so that it can appear in the description of the Google Maps shape.

For example this is with one column (the original export);

If I want to add other descriptors, I change the data table in Google Maps like this:

But I want to replicate this behaviour from the original export in R. I have tried to change the description parameter to add a vector a column names or even and index of column names (i.e. c("Column2", "Column3") or 1:2) and I have tried to add HTML to the description column (which does not work when visualizing in the Google Maps data table in different columns obviously).

How can I achieve this?

Answer 1

You'll have to use HTML and concat the columns together.

sc<- c(103.8259077,1.320045,103.8265944,1.3143817,103.829813,1.3132662, 103.8346624,1.3173421,103.8259077,1.320045)
polys_coords<-list()
polys_coords[[1]]<-matrix(sc,  byrow=TRUE, ncol=2)
polys_coords[[2]]<-polys_coords[[1]]+0.05
polys_coords[[3]]<-polys_coords[[1]]-0.05
polys_spatial<-SpatialPolygons(
  Srl= list ( Polygons( srl=lapply(polys_coords, function(x) Polygon(x)), ID="1"),
              Polygons( srl=lapply(polys_coords, function(x) Polygon(x-0.01)), ID="2"),
              Polygons( srl=lapply(polys_coords, function(x) Polygon(x+0.01)), ID="3"))
)
proj4string(polys_spatial)<-CRS(" +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0")
df<-SpatialPolygonsDataFrame(polys_spatial, data.frame(NAME=paste0("Name",1:3), DESCA=paste0("Poly",1:3), DESCB=paste0("Gon",1:3)))
#   NAME DESCA DESCB
# 1 Name1 Poly1  Gon1
# 2 Name2 Poly2  Gon2
# 3 Name3 Poly3  Gon3

xOut<-sapply(df@polygons, function(x) kmlPolygon(x, name=as.data.frame(df)[x@ID,"NAME"], 
                                                 description=paste( 
                                                               sapply(2:3, function(i) {
                                                                 y<-as.data.frame(df) 
                                                                 paste0("<p><strong>",colnames(y)[i], "</strong>: ", y[x@ID,i],"</p>") } ) , 
                                                              collapse=""))
)

xOut[["content",1]][1:5]
# [1] ""                                                                                                                
# [2] "<Placemark>"                                                                                                     
# [3] "<name>Name1</name>"                                                                                              
# [4] "<description><![CDATA[<p><strong>DESCA</strong>: Poly1</p><p><strong>DESCB</strong>: Gon1</p>]]></description>"
# [5] "<styleUrl>#1</styleUrl>" 
xOut[["content",2]][1:5]
# [1] ""                                                                                                                
# [2] "<Placemark>"                                                                                                     
# [3] "<name>Name2</name>"                                                                                              
# [4] "<description><![CDATA[<p><strong>DESCA</strong>: Poly2</p><p><strong>DESCB</strong>: Gon2</p>]]></description>"
# [5] "<styleUrl>#2</styleUrl>"