[R] upside down image/data

[Jenny Barnes]

Thomas,

Thank you for this example, makes it easier to see what levelplot does - does 
this mean that EVERY time I want to plot with levelplot() I have to not only 
reverse the columns [,ncol(output.temp):1] but also have to transform the matrix 
as below? I am only suprised as I don't remember having read about this in the 
R-info in ?levelplot or R-help website and it seems like a fundamental thing to 
know if using levelplot! 

Thanks,

Jenny

>
>	rm(list=ls(all=TRUE))
>	graphics.off()
>	# make a test matrix:
>	nr<- 3
>	nc<- 4
>	# the data:
>	( m<- matrix((1:(nr*nc)), nr, nc) )
>	     [,1] [,2] [,3] [,4]
>	[1,]    1    4    7   10
>	[2,]    2    5    8   11
>	[3,]    3    6    9   12
>
>	# the way that levelplot (and image) displays the data:
>	t(m)[dim(t(m))[1]:1, ]
>	     [,1] [,2] [,3]
>	[1,]   10   11   12
>	[2,]    7    8    9
>	[3,]    4    5    6
>	[4,]    1    2    3
>
>	# undo what levelplot does by performing the inverse transformation
>	inverse<- function(x) t(x[dim(x)[1]:1, ]) 
>
>	windows(); levelplot(m, main="levelplot(m)")
>	windows(); levelplot(inverse(m), main="levelplot(inverse(m))")
>
>	> Message: 7
>	> Date: Mon, 11 Dec 2006 12:28:17 +0000 (GMT)
>	> From: Jenny Barnes <jmb at mssl.ucl.ac.uk>
>	> Subject: [R] upside down image/data
>	> To: r-help at stat.math.ethz.ch
>	> Message-ID: <200612111228.kBBCSHrj013960 at msslhb.mssl.ucl.ac.uk>
>	> Content-Type: TEXT/plain; charset=us-ascii
>	> 
>	> Dear R-community,
>	> 
>	> I am looking for some simple advice - I have a matrix (therefore 2 
dimensional) 
>	> of global temperature. 
>	> 
>	> Having read R-help I think that when I ask R to image() or levelplot() 
my matrix 
>	> will it actually appear upside down - I think I therefore need to use 
the line:
>	> > levelplot(temperature.matrix[,ncol(output.temp):1], ........)
>	> to get it looking like it was on the globe due to the matrix rows 
increasing in 
>	> number down the matrix in its dimensions on longitude and latitude but 
the 
>	> y-axis coordinates increase up the axis.
>	> 
>	> Can anyone simply tell me whether this is correct as I find it very 
hard to know 
>	> which way up my data should be and I cannot tell which is correct 
simply by 
>	> looking at it!
>	> 
>	> Many thanks for your time in reading this problem,
>	> 
>	> Jenny Barnes
>
>

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jennifer Barnes
PhD student - long range drought prediction
Climate Extremes
Department of Space and Climate Physics
University College London
Holmbury St Mary, Dorking
Surrey
RH5 6NT
01483 204149
07916 139187
Web: http://climate.mssl.ucl.ac.uk