Hi all, Thanks to Markus Loecher and colleagues we can now easily obtain background maps from Google Earth and use it for plotting/interpretation of spatial data. This runs pretty smoothly (e.g. a map of the Netherlands):
library(RgoogleMaps)
# obtain the API key and save into the home folder;
MyMap <- GetMap.bbox(center=c(52.1551723,5.3872035), zoom=7, destfile="netherlands.png", maptype
="hybrid") Read 1 item [1] "http://maps.google.com/staticmap?center=52.1551723,5.3872035&zoom=7&size=640x640 + &maptype=hybrid&format=png32&key=****&sensor=true" trying URL 'http://maps.google.com/staticmap?center=52.1551723,5.3872035&zoom=7&size=640x640 + &maptype=hybrid&format=png32&key=****=true' Content type 'image/png' length 703541 bytes (687 Kb) opened URL downloaded 687 Kb netherlands.png has GDAL driver PNG and has 640 rows and 640 columns
PlotOnStaticMap(MyMap, lat=52.1551723, lon=5.3872035)
But how to convert this image into a SpatialGridDataFrame to allow overlays, export to GIS formats etc? I am not even sure what the correct proj4string for this image is?
str(MyMap) # this only gives coordinates of the centre
List of 4 $ : num 52.2 $ : num 5.39 $ : num 7 $ : num [1:640, 1:640] 187 60 66 1 66 202 151 1 214 220 ... ..- attr(*, "COL")= chr [1:256] "#88887C" "#887440" "#747838" "#0C1C20" ... ..- attr(*, "type")= chr "rgb"
GDALinfo("netherlands.png")
# the coordinates are not embedded! Thanks, Tom Hengl http://home.medewerker.uva.nl/t.hengl/