> Is there any R software that create an image from Yahoo maps together
> with points of known UTM coordinates (or lat/long marked? Note that my
> region of interest is not covered in sufficient detail by Google maps.
> It actually does not have to be Yahoo maps as long as it has
> sufficient coverage of my region but that's the one I have found with
> coverage of my region. The scale I am interested in is a city block.
> Thanks.
rgdal in combination with sp. You'll need to georegister the image, as
the yahoo maps interface is unlikely to provide a format supporting this
metadata, but you can do that easily with two reference coordinates.
The workflow might go like this (untested). You could continue the
query on R-Sig-Geo. Hope this helps.
There are freely available tools for reading image data directly from
Yahoo, Google and Virtual Earth in georeferenced
versions, but I've only used them via commercial GIS. If you can
describe the map you want I'd be interested in
exploring that option.
Cheers, Mike.
library(rgdal)
im <- readGDAL("yahooMap.png") ## a file saved from Yahoo Maps
## create index for RGB colours
col <- SGDF2PCT(im) ## im is a spatialGridDataFrame with 3 bands
im$ind <- col$idx ## add the colour index to the data frame
image(im, "ind", col = col$ct)
## BUT you won't be able to plot UTM on this yet
## you'll need to create a new GridTopology with appropriate
cellcentre.offset and cellsize
ogt <- getGridTopology(im)
. . . find values for offsets and pixel size
gt <- GridTopology(cc.offset, csize, gt at cells.dim)
## recreate the object
im <- SpatialGridDataFrame(gt, im at data)
image(im, "idx", col = col$ct)
points(utm.x, utm.y) ## etc.