Hi,

For next time included the commands, I thought it would be easier to send
the data attached. Thank you both for all advise given to solve the convert
image to SpatialGridDataFrame. This work is part of a proyect (
http://ifop-bevan.pbworks.com/) on demersal fisheries.

Regards,

fernando

On Thu, Sep 24, 2009 at 9:07 AM, Michael Sumner <mdsumner@gmail.com> wrote:

> I put it on the wiki page, hopefully not too obscure - I certainly
> encounter that particular issue quite frequently.
>
> Regards, Mike.
>
> On Thu, Sep 24, 2009 at 8:37 PM, Roger Bivand <Roger.Bivand@nhh.no> wrote:
> > On Thu, 24 Sep 2009, Michael Sumner wrote:
> >
> >> Hello, Roger's reply to this made me realize I replied only to
> >> fernando, so I wanted to correct my first message and add some more.
> >>
> >> This reminds me that image2Grid needs check for irregular x or y
> >> values - it assumes the relationship of the first 2 in each define
> >> them all, so it should error in this case.
> >
> > Sorry, I was looking at the x's - the longitude, not the y's where the
> > problem was. Had the commands been included, it would have been easier to
> > deconstruct. I'm committing a test in image2Grid() which gains a digits=
> > argument to set the tolerance of uniqueness of step difference testing.
> With
> > the check in place, the example data fails.
> >
> > Paul Hiemstra put an interpolation on the R-wiki yesterday at:
> >
> > http://wiki.r-project.org/rwiki/doku.php?id=tips:spatial-data:change_crs
> >
> > perhaps you could add your example to it as well as posting?
> >
> > Roger
> >
> >>
> >> I'll try to put together an example that doe the resampling in R with
> >> overlay, or its underlying functions, to avoid external calls to GDAL.
> >>
> >> The y values in the example data are irregular and so this is not
> >> supported by
> >> Spatial[Grid/Pixels]DataFrame - although this is supported by image()
> >> for xyz lists of this type.
> >>
> >> range(diff(met$y))
> >> [1] 0.09527307 0.13665998
> >>
> >> You can convert this to points like this:
> >>
> >> library(sp)
> >> x <- data.frame(expand.grid(x = met$x, y = met$y), z = as.vector(met$z))
> >> coordinates(x) <- ~x+y
> >>
> >> If you know the projection and there is a regular transform that works
> >> - this is common in NetCDF files and environmental models where an
> >> underlying Mercator grid is use in lat/long form - only Y is
> >> "irregular". Having a wild guess:
> >>
> >> library(rgdal)
> >> proj4string(x) <- CRS("+proj=longlat +ellps=WGS84")
> >> x2 <- spTransform(x, CRS("+proj=merc +ellps=WGS84"))
> >> gridded(x2) <- TRUE
> >>
> >> image(x2)
> >>
> >> That works to create a regular grid and you could transform companion
> >> datasets in the same way, but may not be useful depending on your
> >> application. If you need to warp the grid to regular raster you can do
> >> that externally - with the GDAL command line utilities, which I have
> >> in my path. E.g.
> >>
> >> writeGDAL(x2, "file2convert.tif")
> >> system("gdalwarp file2convert.tif LL.tif -t_srs \"+proj=longlat
> >> +ellps=WGS84\"")
> >>
> >> ll.x <- readGDAL("LL.tif")
> >> summary(ll.x)
> >> Object of class SpatialGridDataFrame
> >> Coordinates:
> >>      min       max
> >> x -77.35186 -64.60699
> >> y -58.38184 -41.03831
> >> Is projected: FALSE
> >> proj4string : [+proj=longlat +ellps=WGS84 +no_defs]
> >> Number of points: 2
> >> Grid attributes:
> >> cellcentre.offset  cellsize cells.dim
> >> x         -77.28616 0.1313904        97
> >> y         -58.31615 0.1313904       132
> >> Data attributes:
> >>  Min.  1st Qu.   Median     Mean  3rd Qu.     Max.
> >> 0.003633 0.438200 0.438200 0.426500 0.438200 0.983700
> >>
> >> image(ll.x)
> >> contour(met, add = TRUE)
> >>
> >> HTH
> >>
> >> Regards, Mike.
> >>
> >> _______________________________________________
> >> R-sig-Geo mailing list
> >> R-sig-Geo@stat.math.ethz.ch
> >> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> >>
> >
> > --
> > Roger Bivand
> > Economic Geography Section, Department of Economics, Norwegian School of
> > Economics and Business Administration, Helleveien 30, N-5045 Bergen,
> > Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
> > e-mail: Roger.Bivand@nhh.no
> >
> >
>
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