Message-ID: <522664f80911021356n735ab071j323b2dd0b6a05c1@mail.gmail.com>
Date: 2009-11-02T21:56:23Z
From: Michael Sumner
Subject: flip SpatialGridDataFrame across axis
In-Reply-To: <522664f80911021345v4c65f4dftf28e9b6f9a5a1a33@mail.gmail.com>
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
>
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