Friends: I wish to overlay data points on a contour graph. The following
example produces a nice contour plot, but I have not mastered the concept
of using panel functions to modify plots. Can someone show me how to
overlay the data points (given after contour plot statement) on the
contourplot?
--Seth
model <- function(a,b,c,X1,X2) # provide model
function for contour plot
{(exp(a + b*X1 + c*X2)) / (1 + exp(a + b*X1 + c*X2))}
g <- expand.grid(X1 = seq(0.40, 0.8,0.01), X2 = seq(0.03,0.99,0.03)) #
create gridded data for contour plot
a <- -37.61 # Assign value to 'a' parameter
b <- 34.88 # Assign value to 'b' parameter
c <- 28.44 # Assign value to 'c' parameter
g$z<- model(a, b, c, g$X1,g$X2) # Create variable z
using gridded data, model, and variables
contourplot(z ~ X1 * X2, # specify the basic
equation for the contour plot
data=g, # Specify the data frame to be
used
contour=TRUE, # Make sure it adds
contours
xlim=c(0.4,0.8), ylim=c(0.401,0.999), zlim=c(0,1), # Set axis
ranges
xlab="p(H)", ylab="p(H|H)", # Add axis labels
region = TRUE, # Add nice colors
cuts=10 # Specify number of contour
slices
)
# Data to superimpose as xyplot on the contourplot....
ph <-c(0.42,0.47,0.59,0.40) # Create a vector of values
under variable 'ph'
phh <-c(0.76,0.81,0.82,0.71) # Create vector of
values for variable 'phh'
d <- data.frame(ph,phh) # Group variables ph
& phh in data frame 'd'
Dr. Seth W. Bigelow
Biologist, Sierra Nevada Research Center
Pacific Southwest Research Station, USDA Forest Service
Mailing address: 2121 2nd St Suite A101, Davis CA 95616
www.fs.fed.us/psw/programs/snrc/staff/bigelow
www.smbigelow.net
Phone: 530 759 1718
Fax: 530 747 0241
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