[R-sig-Geo] overlay 1D graph on a map or map image: van Langren data

[Michael Friendly]

Hi
I'm working with some historical data on determinations of longitude 
used by Michael F van Langren
in 1644 to draw what is believed to be the first graph of statistical 
data. The values are estimates
of the distance in longitude between Toledo and Rome.

G. Iansonius      17.736  1501  Jan Jansson              Flanders    
[1588-1664] sb:~ 1615
G. Mercator       19.872  1567  Gerardus Mercator        Flanders
I. Schonerus      20.638  1536  Johann Schöner           Germany
P. Lantsbergius   21.106  1530  Phillip van Lansberge    Belgium
T. Brahe          21.447  1578  Tycho Brahe              Denmark
I. Regiomontanus  25.617  1471  Johann Muller            Germany      
[1436-1476] sb: 1463
Orontius          26.000  1542  Oronce Finé              France       
[1494-1555] 
C. Clavius        26.340  1567  Christoph Clavius        Germany  
C. Ptolomeus      27.787   150  Claudius Ptolemaeus      Alexandria
A. Argelius       28.170  1610  Andrea Argoli            Italy        
sb: 1610
A. Maginus        29.787  1582  Giovanni Antonio Magini  Italy
D. Origanus       30.128  1601  David Origanus           Germany

I want to show these overlaid on a map, something like the following:

http://euclid.psych.yorku.ca/SCS/Gallery/images/Private/Langren/langren-google-overlay.jpg

using *either* a jpeg image,
http://euclid.psych.yorku.ca/SCS/Gallery/images/Private/Langren/google-toledo-rome3.jpg
or a comparable portion of the world map, something like

# approximate coordinates of the BBox of this map
bbox <- c( 38.186, -9.184,
           43.692, 28.674 )
bbox <- matrix(bbox, 2, 2, byrow=TRUE)
map("world", xlim=bbox[,2], ylim=bbox[,1], fill=TRUE, col=colors())
map.axes()

I created the overlay by manually rescaling and calibrating his graph 
with a portion of a Google map.
But I'd like to be able to do this more exactly in R, possibly using 
other data.

I can read in  the data as follows:

langren <- 
read.csv("http://euclid.psych.yorku.ca/SCS/Gallery/Private/langrens.csv", 
header=TRUE)

# Lat/Long of Toledo & Rome, from Google map

toledo <- c(39.86, -4.03)
rome   <- c(41.89, 12.5)

# locations of the estimates, converted to lat, long
locations <- cbind( rep(rome[1], 12), toledo[2] + langren$long)
rownames(locations) <- langren$name
locations <- rbind( toledo, locations)
colnames(locations) <- c("lat", "long")

The above steps give:

locations <-
structure(c(39.86, 41.89, 41.89, 41.89, 41.89, 41.89, 41.89,
41.89, 41.89, 41.89, 41.89, 41.89, 41.89, -4.03, 13.706, 15.842,
16.608, 17.076, 17.417, 21.587, 21.97, 22.31, 23.757, 24.14,
25.757, 26.098), .Dim = c(13L, 2L), .Dimnames = list(c("toledo",
"G. Iansonius", "G. Mercator", "I. Schonerus", "P. Lantsbergius",
"T. Brahe", "I. Regiomontanus", "Orontius", "C. Clavius", "C. Ptolomeus",
"A. Argelius", "A. Maginus", "D. Origanus"), c("lat", "long")))

I can also read the .jpg Google map image, at least from a local file:

# read the google image
library(rimage)
gimage <- 
read.jpeg("C:/Documents/milestone/images/vanLangren/google-toledo-rome3.jpg")

#gimageloc <- 
"http://euclid.psych.yorku.ca/SCS/Gallery/images/Private/Langren/google-toledo-rome3.jpg"
#dest <- paste(tempfile(),'.jpg', sep='')
#download.file(gimageloc, dest)
#  why doesn't this work?
#gimage <- read.jpeg(dest)

plot(gimage)
# approx  pixel coordinates of Toledo and Rome in the image, measured 
from the *top left* corner as (0,0)
toledo.map <- c(130, 119)
rome.map <-(505, 59)

Here's where I'm stumped.  How can I recreate a version of van Langren's 
graph shown on top of
either the gimage or on top of the portion of the R world map?

thanks
-Michael

-- 
Michael Friendly     Email: friendly AT yorku DOT ca 
Professor, Psychology Dept.
York University      Voice: 416 736-5115 x66249 Fax: 416 736-5814
4700 Keele Street    http://www.math.yorku.ca/SCS/friendly.html
Toronto, ONT  M3J 1P3 CANADA