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 <[email protected]> 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 <[email protected]> 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 > >> [email protected] > >> 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: [email protected] > > > > > > _______________________________________________ > R-sig-Geo mailing list > [email protected] > https://stat.ethz.ch/mailman/listinfo/r-sig-geo > [[alternative HTML version deleted]] _______________________________________________ R-sig-Geo mailing list [email protected] https://stat.ethz.ch/mailman/listinfo/r-sig-geo
