[R-sig-Geo] Displaying temporal variation of raster data

[Jan Verbesselt]

Hi Thiago,

yes, certainly. Without an R script or data is it not so easy to help you. Here are some tips and packages which might be helpful:

- raster package; reading netcdf files
- use getValues() from the raster package to extract the data
- ggplot2 package for creating great graphs
- see http://had.co.nz/ggplot2/geom_bar.html for categorical histogram examples.
- maybe melt() of the ggplot2 package might be handy to prepare your data set.

A very simple example:
library(raster) 
library(ggplot2)
m <- matrix(1:100, nr=10)
n <- matrix(c(rep(1,30),rep(2,70)), nr=10)
r <- raster(m, xmn=167620, xmx=171745, ymn=443660, ymx=448110) 
deforest <- raster(n, xmn=167620, xmx=171745, ymn=443660, ymx=448110)
df <- data.frame(rate=getValues(r), class=getValues(deforest))
ggplot(df, aes(x=factor(class), fill=factor(class))) + geom_bar()


Cheers,
Jan

On 15/03/2012, at 3:34 AM, Thiago Veloso wrote:

> Dear R colleagues,
> 
> I have a netcdf file containing ten time slices, where each slice corresponds to yearly deforestation rates over the Amazon forest. Values range from 0 (no deforest) to 1 (maximum deforest). Please take a look in a sample of the data: http://imageshack.us/photo/my-images/23/deforestamazon.png/
> 
> My objective is to show the temporal variation of this data. How can I produce categorical histograms for each one of the ten years? What I have in mind is something like the lower panel of this figure: http://www.crwr.utexas.edu/gis/gishydro05/Time/DHI_Temporal_Analyst/TemporalAnalystForArcGIS.htm, but plotting bars relative to three or four classes of deforesting rates instead of lines.
> 
> Is it possible to produce such a figure using any SIG-related R package?
> 
> Many thanks in advance,
> Thiago.
> 
> 
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