plotKML: image width and height of legend in KML file

We did not consider legends for point data because users will most 
likely use multiple esthetics parameters (color, size, altitude), so yes 
you need to use the lower level functions "kml_open", "kml_layer" to 
achieve this :(
Also 'width' and 'height' arguments only really make sense for factor 
type variables (hence the easiest is that you then make the legend 
yourself and then insert it using "kml_screen").

Notice that you need to use "z.lim" 2 times to ensure that the legend 
matches the colors of points. Here is an example:

R> library(plotKML)
R> library(sp)
R> library(rgdal)
R> data(eberg)
R> coordinates(eberg) <- ~X+Y
R> proj4string(eberg) <- CRS("+init=epsg:31467")
R> eberg <- eberg[runif(nrow(eberg))<.1,]
R> shape = "http://maps.google.com/mapfiles/kml/pal2/icon18.png"
R> kml_open("eberg_CLYMHT_A.kml")
KML file opened for writing...
R> kml_layer(eberg["CLYMHT_A"], colour=CLYMHT_A, z.lim=c(20,60),
+    colour_scale=SAGA_pal[[1]], shape=shape, points_names="")
Reprojecting to +proj=longlat +datum=WGS84 ...
Writing to KML...
R> kml_legend.bar(x=eberg$CLYMHT_A, legend.file="kml_legend.png",
+    legend.pal=SAGA_pal[[1]], z.lim=c(20,60))
null device
           1
R> kml_screen(image.file="kml_legend.png")
R> kml_close("eberg_CLYMHT_A.kml")
Closing  eberg_CLYMHT_A.kml

If you need to do this N times, then the best is to make a function e.g.:

R> kml_points <- function(obj, file, z.lim, points_names="", ...){
   kml_open(file)
   kml_layer(obj, colour=obj at data[,1], 
shape="http://maps.google.com/mapfiles/kml/pal2/icon18.png", 
colour_scale=SAGA_pal[[1]], points_names="", ...)
   kml_legend.bar(x=obj at data[,1], legend.file=gsub(".kml", ".png", 
file), legend.pal=SAGA_pal[[1]], z.lim=z.lim)
   kml_screen(image.file=gsub(".kml", ".png", file))
   kml_close(file)
}
## test it:
R> kml_points(eberg["CLYMHT_A"], file="eberg_CLYMHT_A.kml", z.lim=c(20,60))

FYI, the kml_legend.bar function is at:

https://r-forge.r-project.org/scm/viewvc.php/pkg/R/legend.bar.R?view=markup&root=plotkml

HTH,

T. Hengl

Hello,

With my first plotKML project I managed to create a KML file containing a layer with irregular points (air temperature data) and add a legend overlay to it.
I tried changing the size of the legend to no avail, whatever I fill in for "width" and "height" I get a png file that is 120x240 pixels.
What am I doing wrong?

Cheers,
JanE

My code is:
library(sp)
library(plotKML)
library(spacetime)
#
# working directory
setwd('D:/A-user/Hi-Aware/plotKML')
#
# input file
tripfile <- 'wbgt_input_data_new.csv'
tripdata <- read.csv(tripfile)
#
# convert time to POSIX
tripdata$ctime <- as.POSIXct(strptime(tripdata$timestamp,"%Y-%m-%d %H:%M:%S"),format="%Y-%m-%d %H:%M:%S")
#
# lat lon with decimal minutes
tripdata$lat <- tripdata$lat + tripdata$latmin/60.
tripdata$lon <- tripdata$lon + tripdata$lonmin/60.
#
# create STIDF object
sp <- SpatialPoints(tripdata[,c("lon","lat")])
proj4string(sp) <- CRS("+proj=longlat +datum=WGS84")
tripdata.st <- STIDF(sp, time = tripdata$ctime, data = tripdata[,c("t2m","rh")])
#
# save to kml with legend bar overlay
kml_open(file.name = paste(tripfile, ".kml", sep=""))
kml_layer(tripdata.st, file.name=paste(tripfile, ".kml", sep=""), colour=t2m, labels="", points_names="",
         shape="http://maps.google.com/mapfiles/kml/pal2/icon18.png", kmz=FALSE, open.kml=TRUE)
kml_legend.bar(x=tripdata$t2m, width=100, height=500, pointsize = 10, legend.file="legend.png",
               legend.pal=SAGA_pal$SG_COLORS_DEFAULT, z.lim = range(tripdata$t2m, na.rm=TRUE, finite=TRUE))
kml_screen(image.file = "legend.png", position = "ML", sname = "legend")
kml_close(file.name = paste(tripfile, ".kml", sep=""))

end of code

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