RgoogleMaps (version 1.0)

RgoogleMaps-package: Utilities to enable overlays on Google Maps

Description

This package serves two purposes: (i) Provide a comfortable R interface to query the Google server for static maps, and (ii) Use the map as a background image to overlay plots within R. This requires proper coordinate scaling.

Details

ll{ Package: RgoogleMaps Type: Package Version: 1.0 Date: 2009-04-01 License: GPL LazyLoad: yes } The two main functions in the package are GetMap, which queries the Google server for a map, and PlotOnStaticMap, which enables the actual overlay plots in R.

The examples below give a bit of support code for using the functions in this package. Details on using the functions themselves can be found in the documentation for those functions.

NOTE: The Google Static Maps API requires a Maps API key. If you haven`t already done so, sign up for a free API key at http://code.google.com/apis/maps/signup.html

Examples

#This section contains examples that will execute once you obtain an API key:
	
#The first step naturally will be to download a static map from the Google server. A simple example:

  GetMap(markers = '40.702147,-74.015794,blues%7C40.711614,-74.012318,greeng%7C40.718217,-73.998284,redc', destfile = "MyTile1.png");
                 
   tmp <- PlotOnStaticMap(MyMap,lat = c(40.702147,40.711614,40.718217), lon = c(-74.015794,-74.012318,-73.998284), cex=1.5,pch=20,col=c('red', 'blue', 'green'), add=F)
#Of course, one can do without the markers and/or just pass a bounding box:

  GetMap(center=c(40.714728,-73.99867), zoom =14, destfile = "MyTile2.png",maptype = "mobile");
  
#The function qbbox() basically computes a bounding box for the given lat,lon points with a few additional options such as quantile boxes, additional buffers, etc.  

  bb <- qbbox(c(40.702147,40.711614,40.718217),c(-74.015794,-74.012318,-73.998284), 
            TYPE = "all", margin = list(m=rep(5,4), TYPE = c("perc", "abs")[1]));
            
      MyMap <- GetMap.bbox(bb$lonR, bb$latR,destfile = "MyTile3.png", maptype = "satellite")
  
#The main function that overlays points (can easily be extended to lines or any other object) is PlotOnStaticMap().
#The following simple sequence of calls serves to test the coincidence of the markers placed by Google and the corresponding points overlaid by PlotOnStaticMap(). Note that we convert the map to grayscale first to make the colored points more discernible.

#Define the markers:

  mymarkers <- cbind.data.frame(lat = c(38.898648,38.889112, 38.880940), 
          lon = c(-77.037692, -77.050273, -77.03660), size =  c('tiny','tiny','tiny'), 
          col = c('blue', 'green', 'red'), char = c('','',''));

#get the bounding box:

  bb <- qbbox(lat = mymarkers[,"lat"], lon = mymarkers[,"lon"])
  
#download the map:

  MyMap <- GetMap.bbox(bb$lonR, bb$latR, destfile = "DC.png", GRAYSCALE =T,
                markers = mymarkers);
                
#determine the max zoon, so that all points fit on the plot (not necessary in this case):  

   zoom <- min(MaxZoom(latrange=bb$latR,lonrange=bb$lonR)));
   
#plot:
 
 png("OverlayTest.png",640,640);
  
  tmp <- PlotOnStaticMap(MyMap,lat = mymarkers[,"lat"], lon = mymarkers[,"lon"], 
         cex=1.5,pch=20,col=c('blue', 'green', 'red'), add=F);
         
  tmp <- PlotOnStaticMap(MyMap,lat = mymarkers[,"lat"], lon = mymarkers[,"lon"], 
       col=c('purple'), add=T, FUN = lines, lwd = 2)
       
  dev.off()