7 messages · Sébastien Bihorel, Edzer Pebesma, Michael Sumner
Hi, After importing a grid with readGDAL(), a `SpatialGridDataFrame' object is produced that looks correct, except the y-axis is flipped upside down, despite the note in the "Value" section in ?readGDAL. So I need to flip the grid across the horizontal axis, and searching the archives points to an old reference to elide() in maptools. However, this doesn't take a `SpatialGridDataFrame', so I'd appreciate any suggestions for better alternatives. Thanks. Cheers,
Seb
Hi Sebastian, I think the "north-south" note is referring to possibly-rotated grids (using the transform values supported by many formats) - not to "north vs. south" in orientation. You can easily flip a grid by reverting it (one band at a time) to an xyz image and using indexing. I find this approach the least confusing and easily repeatable. library(rgdal) data(meuse.grid) coordinates(meuse.grid) <- ~x+y gridded(meuse.grid) <- TRUE fullgrid(meuse.grid) <- TRUE image(meuse.grid[3]) ## note this method only works on single bands at once x1 <- as.image.SpatialGridDataFrame(meuse.grid[3]) ## reverse the Y by indexing in to the (image) xyz list x1$z <- x1$z[,ncol(x1$z):1] ## convert to SGDF flipY <- image2Grid(x1, p4 = as.character(proj4string(meuse.grid))) contour(flipY, add = TRUE) It would not be difficult to adapt this to flip each band sequentially, and use the internal arrangement of the SpatialGrid/Pixels classes directly - but this is enough for me. Regards, Mike.
Hi, After importing a grid with readGDAL(), a `SpatialGridDataFrame' object is produced that looks correct, except the y-axis is flipped upside down, despite the note in the "Value" section in ?readGDAL. ?So I need to flip the grid across the horizontal axis, and searching the archives points to an old reference to elide() in maptools. ?However, this doesn't take a `SpatialGridDataFrame', so I'd appreciate any suggestions for better alternatives. ?Thanks. Cheers, -- Seb
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On Tue, 3 Nov 2009 07:40:59 +1100,
Hi Sebastian, I think the "north-south" note is referring to possibly-rotated grids (using the transform values supported by many formats) - not to "north vs. south" in orientation.
You can easily flip a grid by reverting it (one band at a time) to an xyz image and using indexing. I find this approach the least confusing and easily repeatable.
[...] Thanks for the quick reply Mike!! Cheers,
Seb
It would be nice if the "[" methods on ?'SpatialGridDataFrame-class'
could perform the same indexing orientation, but that uses the
row/column values for [i,j,...] to obtain the subsetted cells which
are regridded via SpatialPixels - so the direction is lost. I'm not
sure it's a good idea to modify that - given that the indexing could
be used to subset at the same time - which is probably why the authors
have written it that way. ;)
But, I've been meaning to try something like this for ages, and this
seems to work:
flipHorizontal <- function(x) {
if (!inherits(x, "SpatialGridDataFrame")) stop("x must be a
SpatialGridDataFrame")
grd <- getGridTopology(x)
idx = 1:prod(grd at cells.dim[1:2])
m = matrix(idx, grd at cells.dim[2], grd at cells.dim[1], byrow =
TRUE)[,grd at cells.dim[1]:1]
idx = as.vector(t(m))
x at data <- x at data[idx, TRUE, drop = FALSE]
x
}
flipVertical <- function(x) {
if (!inherits(x, "SpatialGridDataFrame")) stop("x must be a
SpatialGridDataFrame")
grd <- getGridTopology(x)
idx = 1:prod(grd at cells.dim[1:2])
m = matrix(idx, grd at cells.dim[2], grd at cells.dim[1], byrow =
TRUE)[grd at cells.dim[2]:1, ]
idx = as.vector(t(m))
x at data <- x at data[idx, TRUE, drop = FALSE]
x
}
The approach there is stolen from 'subs.SpatialGridDataFrame' in
sp/R/SpatialGridDataFrame-methods.R - so thanks as ever to the
authors!
Cheers, Mike.
On Tue, 3 Nov 2009 07:40:59 +1100, Michael Sumner <mdsumner at gmail.com> wrote:
Hi Sebastian, I think the "north-south" note is referring to possibly-rotated grids (using the transform values supported by many formats) - not to "north vs. south" in orientation.
You can easily flip a grid by reverting it (one band at a time) to an xyz image and using indexing. I find this approach the least confusing and easily repeatable.
[...] Thanks for the quick reply Mike!! Cheers, -- Seb
_______________________________________________ R-sig-Geo mailing list R-sig-Geo at stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
Ergh, sorry for the update - a pox on Gmail for sabotaging my
attempts at plain text! I've attached the functions in a text file to
avoid [ampersand] to " at " conversion ...
---------- Forwarded message ----------
From: Michael Sumner <mdsumner at gmail.com>
Date: Tue, Nov 3, 2009 at 8:45 AM
Subject: Re: [R-sig-Geo] flip SpatialGridDataFrame across axis
To: r-sig-geo at stat.math.ethz.ch
It would be nice if the "[" methods on ?'SpatialGridDataFrame-class'
could perform the same indexing orientation, but that uses the
row/column values for [i,j,...] ?to obtain the subsetted cells which
are regridded via SpatialPixels - so the direction is lost. I'm not
sure it's a good idea to modify that - given that the indexing could
be used to subset at the same time - which is probably why the authors
have written it that way. ?;)
But, I've been meaning to try something like this for ages, and this
seems to work:
flipHorizontal <- function(x) {
? ? ? ?if (!inherits(x, "SpatialGridDataFrame")) stop("x must be a
SpatialGridDataFrame")
? ? ? ?grd <- getGridTopology(x)
? ? ? ?idx = 1:prod(grd at cells.dim[1:2])
? ? ? ?m = matrix(idx, grd at cells.dim[2], grd at cells.dim[1], byrow =
TRUE)[,grd at cells.dim[1]:1]
? ? ? ?idx = as.vector(t(m))
? ? ? ?x at data <- x at data[idx, TRUE, drop = FALSE]
? ? ? ?x
}
flipVertical <- function(x) {
? ? ? ?if (!inherits(x, "SpatialGridDataFrame")) stop("x must be a
SpatialGridDataFrame")
? ? ? ?grd <- getGridTopology(x)
? ? ? ?idx = 1:prod(grd at cells.dim[1:2])
? ? ? ?m = matrix(idx, grd at cells.dim[2], grd at cells.dim[1], byrow =
TRUE)[grd at cells.dim[2]:1, ]
? ? ? ?idx = as.vector(t(m))
? ? ? ?x at data <- x at data[idx, TRUE, drop = FALSE]
? ? ? ?x
}
The approach there is stolen from 'subs.SpatialGridDataFrame' in
sp/R/SpatialGridDataFrame-methods.R - so thanks as ever to the
authors!
Cheers, Mike.
On Tue, 3 Nov 2009 07:40:59 +1100, Michael Sumner <mdsumner at gmail.com> wrote:
Hi Sebastian, I think the "north-south" note is referring to possibly-rotated grids (using the transform values supported by many formats) - not to "north vs. south" in orientation.
You can easily flip a grid by reverting it (one band at a time) to an xyz image and using indexing. I find this approach the least confusing and easily repeatable.
[...] Thanks for the quick reply Mike!! Cheers, -- Seb
_______________________________________________ R-sig-Geo mailing list R-sig-Geo at stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
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Michael, to be hounest, it even surprised me, being the author, that data(meuse.grid) gridded(meuse.grid) = ~x+y fullgrid(meuse.grid) = TRUE image(meuse.grid[104:1,]) would not flip the image. It just works hard to not destroy the spatial location of all individual pixels -- it will select all rows in reverse order, but in the end put everything back in place. What you do is kind of more like image analysis, as it moves the location of pixels, right? Do you mind if we add your flipXxx functions to sp? -- Edzer
Ergh, sorry for the update - a pox on Gmail for sabotaging my
attempts at plain text! I've attached the functions in a text file to
avoid [ampersand] to " at " conversion ...
---------- Forwarded message ----------
From: Michael Sumner <mdsumner at gmail.com>
Date: Tue, Nov 3, 2009 at 8:45 AM
Subject: Re: [R-sig-Geo] flip SpatialGridDataFrame across axis
To: r-sig-geo at stat.math.ethz.ch
It would be nice if the "[" methods on ?'SpatialGridDataFrame-class'
could perform the same indexing orientation, but that uses the
row/column values for [i,j,...] to obtain the subsetted cells which
are regridded via SpatialPixels - so the direction is lost. I'm not
sure it's a good idea to modify that - given that the indexing could
be used to subset at the same time - which is probably why the authors
have written it that way. ;)
But, I've been meaning to try something like this for ages, and this
seems to work:
flipHorizontal <- function(x) {
if (!inherits(x, "SpatialGridDataFrame")) stop("x must be a
SpatialGridDataFrame")
grd <- getGridTopology(x)
idx = 1:prod(grd at cells.dim[1:2])
m = matrix(idx, grd at cells.dim[2], grd at cells.dim[1], byrow =
TRUE)[,grd at cells.dim[1]:1]
idx = as.vector(t(m))
x at data <- x at data[idx, TRUE, drop = FALSE]
x
}
flipVertical <- function(x) {
if (!inherits(x, "SpatialGridDataFrame")) stop("x must be a
SpatialGridDataFrame")
grd <- getGridTopology(x)
idx = 1:prod(grd at cells.dim[1:2])
m = matrix(idx, grd at cells.dim[2], grd at cells.dim[1], byrow =
TRUE)[grd at cells.dim[2]:1, ]
idx = as.vector(t(m))
x at data <- x at data[idx, TRUE, drop = FALSE]
x
}
The approach there is stolen from 'subs.SpatialGridDataFrame' in
sp/R/SpatialGridDataFrame-methods.R - so thanks as ever to the
authors!
Cheers, Mike.
On Tue, Nov 3, 2009 at 7:49 AM, Sebastian P. Luque <spluque at gmail.com> wrote:
On Tue, 3 Nov 2009 07:40:59 +1100,
Michael Sumner <mdsumner at gmail.com> wrote:
Hi Sebastian, I think the "north-south" note is referring to
possibly-rotated grids (using the transform values supported by many
formats) - not to "north vs. south" in orientation.
You can easily flip a grid by reverting it (one band at a time) to an
xyz image and using indexing. I find this approach the least confusing
and easily repeatable.
[...] Thanks for the quick reply Mike!! Cheers, -- Seb
_______________________________________________ R-sig-Geo mailing list R-sig-Geo at stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo ------------------------------------------------------------------------ _______________________________________________ R-sig-Geo mailing list R-sig-Geo at stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
Edzer Pebesma Institute for Geoinformatics (ifgi), University of M?nster Weseler Stra?e 253, 48151 M?nster, Germany. Phone: +49 251 8333081, Fax: +49 251 8339763 http://ifgi.uni-muenster.de/ http://www.springer.com/978-0-387-78170-9 e.pebesma at wwu.de
Hi Edzer, no problem at all - Robert's approach is much less verbose, but I think this explicit method is easier to understand and share as it exposes the underlying indexing. I agree there's a sense that it is image processing, but in the "GIS raster" sense (image, DEM, data, etc.) it's a useful way of correcting broken or incomplete metadata - and with the range of orientation conventions and ways of storing those it's handy to have. Do you think it belongs as a method in the maptools elide family - at least eventually? I guess that depends on future support for rasters there. Given the terminology used there it's probably better to call the functions "reflectHorizontal/Vertical" rather than flip, even if they exist as standalones for now? Regards, Mike. On Tue, Nov 3, 2009 at 7:13 PM, Edzer Pebesma
Michael, to be hounest, it even surprised me, being the author, that data(meuse.grid) gridded(meuse.grid) = ~x+y fullgrid(meuse.grid) = TRUE image(meuse.grid[104:1,]) would not flip the image. It just works hard to not destroy the spatial location of all individual pixels -- it will select all rows in reverse order, but in the end put everything back in place. What you do is kind of more like image analysis, as it ?moves the location of pixels, right? Do you mind if we add your flipXxx functions to sp? -- Edzer Michael Sumner wrote:
Ergh, sorry for the update - ?a pox on Gmail for sabotaging my
attempts at plain text! ?I've attached the functions in a text file to
avoid [ampersand] to " at " conversion ...
---------- Forwarded message ----------
From: Michael Sumner <mdsumner at gmail.com>
Date: Tue, Nov 3, 2009 at 8:45 AM
Subject: Re: [R-sig-Geo] flip SpatialGridDataFrame across axis
To: r-sig-geo at stat.math.ethz.ch
It would be nice if the "[" methods on ?'SpatialGridDataFrame-class'
could perform the same indexing orientation, but that uses the
row/column values for [i,j,...] ?to obtain the subsetted cells which
are regridded via SpatialPixels - so the direction is lost. I'm not
sure it's a good idea to modify that - given that the indexing could
be used to subset at the same time - which is probably why the authors
have written it that way. ?;)
But, I've been meaning to try something like this for ages, and this
seems to work:
flipHorizontal <- function(x) {
? ? ? ?if (!inherits(x, "SpatialGridDataFrame")) stop("x must be a
SpatialGridDataFrame")
? ? ? ?grd <- getGridTopology(x)
? ? ? ?idx = 1:prod(grd at cells.dim[1:2])
? ? ? ?m = matrix(idx, grd at cells.dim[2], grd at cells.dim[1], byrow =
TRUE)[,grd at cells.dim[1]:1]
? ? ? ?idx = as.vector(t(m))
? ? ? ?x at data <- x at data[idx, TRUE, drop = FALSE]
? ? ? ?x
}
flipVertical <- function(x) {
? ? ? ?if (!inherits(x, "SpatialGridDataFrame")) stop("x must be a
SpatialGridDataFrame")
? ? ? ?grd <- getGridTopology(x)
? ? ? ?idx = 1:prod(grd at cells.dim[1:2])
? ? ? ?m = matrix(idx, grd at cells.dim[2], grd at cells.dim[1], byrow =
TRUE)[grd at cells.dim[2]:1, ]
? ? ? ?idx = as.vector(t(m))
? ? ? ?x at data <- x at data[idx, TRUE, drop = FALSE]
? ? ? ?x
}
The approach there is stolen from 'subs.SpatialGridDataFrame' in
sp/R/SpatialGridDataFrame-methods.R - so thanks as ever to the
authors!
Cheers, Mike.
On Tue, Nov 3, 2009 at 7:49 AM, Sebastian P. Luque <spluque at gmail.com> wrote:
On Tue, 3 Nov 2009 07:40:59 +1100, Michael Sumner <mdsumner at gmail.com> wrote:
Hi Sebastian, I think the "north-south" note is referring to possibly-rotated grids (using the transform values supported by many formats) - not to "north vs. south" in orientation. You can easily flip a grid by reverting it (one band at a time) to an xyz image and using indexing. I find this approach the least confusing and easily repeatable.
[...] Thanks for the quick reply Mike!! Cheers, -- Seb
_______________________________________________ R-sig-Geo mailing list R-sig-Geo at stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo ------------------------------------------------------------------------ _______________________________________________ R-sig-Geo mailing list R-sig-Geo at stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
-- Edzer Pebesma Institute for Geoinformatics (ifgi), University of M?nster Weseler Stra?e 253, 48151 M?nster, Germany. Phone: +49 251 8333081, Fax: +49 251 8339763 http://ifgi.uni-muenster.de/ http://www.springer.com/978-0-387-78170-9 e.pebesma at wwu.de