I tried to polygon.....you are right...too  slow

I'm not sure how to resample to get a regular grid...using interp or interpp
would not be wise because of the size of the grid...



On Mon, Jul 13, 2009 at 11:09 AM, Barry Rowlingson <
b.rowlingson@lancaster.ac.uk> wrote:

> On Mon, Jul 13, 2009 at 3:26 PM, Matt Oliver<moliver@udel.edu> wrote:
> > Dear r-sig-geo,
> >
> > I am trying to generate a kml for an image I am producing using image().
> > After reading about kml generation, I'm unsure if I sould be using
> > kmlOverlay() or writeOGR, or some other function.
> >
> > This is the data
> >
> > http://www.ceoe.udel.edu/cms/moliver/20071003.276.0237.n17.nc
> >
> > require(ncdf)
> > require(fields)
> > f <- open.ncdf("20071003.276.0237.n17.nc")
> >
> > lon <- get.var.ncdf(f, "lon")
> > lat <- get.var.ncdf(f, "lat")
> > mcsst <- get.var.ncdf(f, "mcsst")
> > plot(diff(lon)) #####notice decreasing
> > par(mar=c(0, 0, 0, 0))
> > par(bty="n")
> >
> > image(lon, lat, mcsst, col = tim.colors(64)) #####image I want to make
> kml
> > for
> >
> > I don't seem to be able to make a proper "Spatial" object because of the
> > unequally spaced geographic coordinates.This seems to be necessary to to
> > proceed with a kml generation.
> >
> > I'm probably missing something simple so any help or example code would
> be
> > wonderful
> >
>
>  KML does this kind of image overlay by taking an image file (PNG,
> jpeg etc) and it's bounding box in lat-long. It can't cope with
> irregular grids.
>
>  My first thought as a workaround was to turn every pixel into a
> rectangular polygon. But then I got the data and saw we were dealing
> with 1445626 pixels and that google earth would probably crawl...
>
>  So I think you'll need to resample your data onto a regular lat-long
> grid, then save it as an image, and then write the relevant KML with
> the bounds. The KML is quite simple:
>
>
> http://code.google.com/apis/kml/documentation/kml_tut.html#ground_overlays
>
>  but the resampling might not be. I think I've written some resampling
> code somewhere, it just works out where in the old array a bunch of
> regularly spaced points are that will make the new array are, and
> samples. There may be R code for doing interpolation - maybe the
> rimage or RImageJ packages...
>
>  But no, I don't think anything existing can do it [waits for Roger to
> prove him wrong again...].
>
> Barry
>



-- 
Matthew J. Oliver
Assistant Professor
School of Marine Science and Policy
College of Earth, Ocean and Environment
University of Delaware
700 Pilottown Rd.
Lewes, DE, 19958
302-645-4079
http://www.ceoe.udel.edu/people/profile.aspx?moliver

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