qmplot, geom_segment error in visual-traceroute.R, plot_ggmap() function

[brianhigh]

_BUG_: If you see these errors, run the script a second time from R.

• Error: geom_segment requires the following missing aesthetics: x, y
• Error in eval(expr, envir, enclos) : object 'next_longitude' not found

 > source("./visual-traceroute.R")

Tracing route to: www.gov.za ... 
Using zoom = 3...
Error in eval(expr, envir, enclos) : object 'next_longitude' not found

> source("./visual-traceroute.R")

Tracing route to: www.gov.za ... 
Using zoom = 3...
Saving 6.99 x 7 in image

Note: Until this bug is fixed, map.pkg='ggmap' will not work from running the script from the OS command-line shell (e.g., Bash, DOS) using Rscript.

To see this error, you will need to set map.pkg='ggmap' in the script options and either set use.cache=TRUE or remove (if exists) the cached ggmap.png for the host you are mapping before running to the script to force the recreation of the map. Example: images/www_gov_za/ggmap.png.

If you use save.plot=FALSE, you can see that this failure pattern will hold repeatedly ... every other sourcing of the document from the R console gives the error, alternating with no-error, back and forth.

Note, this script starts with rm(list=ls()) so I don't see why the error only shows up on every other sourcing of the script.