[R] R software to place points on Yahoo maps

[Gabor Grothendieck]

Hi, Your response to my post was EXTREMELY useful.

For georegistering I used the site:

   http://www.runningmap.com

which lets one click on a a Yahoo! map and get lat/long in lower right.
As my data is in UTM I converted the lat/long to UTM using:

   http://home.hiwaay.net/~taylorc/toolbox/geography/geoutm.html

Then using locator() in R I picked out the corresponding points on the
R image that I had created using your code.  That allowed me to
calculate the inputs for GridTopology (are there any convenience functions
to assist in this? -- I found it a bit error prone)

(I actually noticed that there is a lat/long in Yahoo! map URLs so it might
be that if the maps are a known width and height that one could georegister
them based only on that.)

At any rate I seem to be having some success with this.  Thanks !!!


On 3/4/07, Michael Sumner <mdsumner at utas.edu.au> wrote:
> > 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.
>
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