CODEWITHSUNDEEP
rlinuxggplot2pngggimage
Aquarius_Girl
Aquarius_Girl

Reputation: 22946

Loading a raster data of map PNG on ggmaps of R

This will be cross posted on R's mailing list.

I have the map as a png, so I won't be using the get_map function. I have extracted the raster data from the png, and I wish to load the map as it is on the display of R, and then I would like to plot a point on it.

So, here's the way I have tried ggmaps. The program is compiling fine. Problem here is that there isn't any output being shown. 

library (png)
library (ggmap)

latitude  = c(40.702147,40.718217,40.711614)
longitude = c(-74.012318,-74.015794,-73.998284)

# Reads a PNG and outputs a raster array.
img <- readPNG (system.file ("img", "My.png", package="png"))

df <- data.frame (latitude, longitude)

# img: raster array read from the map png.
ggimage (img, fullpage = TRUE) + geom_point (data = df, aes_auto (df), size = 2)

qplot (latitude, longitude, data = df, colour = I("red"), size = I(3))

Of course I am doing something wrong. Please point out.

> sessionInfo()
R version 2.15.1 (2012-06-22)
Platform: x86_64-unknown-linux-gnu (64-bit)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=C                 LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] ggmap_2.1     ggplot2_0.9.1 png_0.1-4    

loaded via a namespace (and not attached):
 [1] colorspace_1.1-1   dichromat_1.2-4    digest_0.5.2       grid_2.15.1       
 [5] labeling_0.1       MASS_7.3-18        memoise_0.1        munsell_0.3       
 [9] plyr_1.7.1         proto_0.3-9.2      RColorBrewer_1.0-5 reshape2_1.2.1    
[13] RgoogleMaps_1.2.0  rjson_0.2.8        scales_0.2.1       stringr_0.6       
[17] tools_2.15.1      
>

EDIT: I have found an error. Actually I was first running it with source (uff.R), and this command didn't show any error. Then I tried Rscript.

anisha@linux-y3pi:~> Rscript uff.R
Loading required package: ggplot2
Loading required package: methods
Error in eval(expr, envir, enclos) : object 'x' not found
Calls: print ... sapply -> lapply -> eval.quoted -> lapply -> FUN -> eval
Execution halted

Upvotes: 1

Views: 2356

Answers (2)

Spacedman
Spacedman

Reputation: 94317

Your ggimage is failing because there's no x and y in it. Rename your lat-long coords to x and y. Here is a completely reproducible example. This is basic ggplot stuff:

> library(png)
> library(ggplot2)
> img <- readPNG(system.file("img", "Rlogo.png", package="png"))
> latitude  = c(40.702147,40.718217,40.711614)
> longitude = c(-74.012318,-74.015794,-73.998284)
> df <- data.frame (x=longitude,y=latitude)
> qplot(x,y,data = df, colour = I("red"), size = I(3))

Run those commands on your command line and you should see a plot. Possible reasons for failing are:

  • Your R doesn't have an X11 connection to your display. Is this all running on a local Linux machine? You haven't connected to a server? If R can't pop up a graphics window it will probably try and create an Rplots.pdf file.
  • You are running in a script which isn't printing. Wrap all ggplot, grid, and lattice graphics functions that you want to produce output in print() function calls. This is a FAQ, I think. Paul Hiemstra put this as an answer but then deleted it...

Upvotes: 3

Paul Hiemstra
Paul Hiemstra

Reputation: 60984

When calling grid based plotting libaries (lattice and ggplot2), you need to explicitly print the plot in order to get any output when using it outside of an interactive session:

bla = ggplot(...)
print(bla)

or shorter:

print(ggplot(...))

Upvotes: 1

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