[R-sig-Geo] Loading a raster data of map PNG on ggmaps of R

[Anisha Kaul]

Greetings,

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 an error with
Rscript, and there isn't any output "display window" being shown.
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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))
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The error is:
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anisha at 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
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R info:
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> 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
>
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-- 
Anisha Kaul