I have a file in this format:
http://docs.codehaus.org/display/GEOTOOLS/ArcInfo+ASCII+Grid+format#ASCIIGrid
The first rows look like this:
ncols 1440
nrows 720
xllcorner -180.0
yllcorner -90
cellsize 0.25
NODATA_value -9999
Basically I have the world with 1440 'tiles' in x direction (longitude) and
720 'tiles' in y direction (latitude). Each 'tile' is a square with a length
of 0.25 degrees. I think I have xllcorner and yllcorner correct. I can draw
this map like this in R:
library("adehabitat")
bio1 <- import.asc("D:/ENFA/data.asc")
maps <- as.kasc(list(data = bio1))
image(maps, col = cm.colors(256), clfac = list(Aspect = cl))
The map looks fine.
I would like to perform some ecological niche factor analysis (ENFA) using
the adehabitat package and am not too sure about the location data.
Basically I have them as longitudes and latitudes at the moment but I could
also generate then as 'tile index' (e.g. lower left corner has the latitude
-90 and longitude -180 so the 'tile index' would be 0, 0 - right?). Which is
the correct location data format? I would use ENFA code like this:
locs <- read.table("D:/ENFA/Locs.txt", header = TRUE, sep="\t")
dataenfa1 <- data2enfa(maps, locs)
pc <- dudi.pca(dataenfa1$tab, scannf = FALSE)
enfa1 <- enfa(pc, dataenfa1$pr,scannf = FALSE)
hist(enfa1)
I would appreciate any comments please. Thanks in advance.
Christian
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