agenbagFilters {imagine} | R Documentation |
Performs algorithms from Agenbag et al. (2003)
Description
This function performs two (gradient) calculation approaches for SST, as outlined in the paper by Agenbag et al. (2003).
Usage
agenbagFilters(X, algorithm = c(1, 2), ...)
Arguments
X |
A numeric |
algorithm |
|
... |
Not used. |
Details
Section 2.2.4 of the paper by Agenbag et al. (2003) introduces the following two methods:
- Method 1:
Based on the equation
Y_{i,j}=\sqrt{(X_{i+1,j}-X_{i-1,j})^2 +(X_{i,j+1}-X_{i,j-1})^2}
where Y_{i,j}
represents the output value for each X_{i,j}
pixel value
of a given X
matrix.
- Method 2:
the standard deviation in a 3x3 pixel area centered on position
(i,j)
.
As outlined in the original study, this method conducts searches within a 1-pixel vicinity of each point. For method 1, it only returns a value for points where none of the four involved values are NA. Conversely, for method 2, the standard deviation calculation is performed only for points where at least 3 non-NA values are found in the 3x3 neighborhood.
Value
agenbagFilters
returns a matrix
object with the same
dimensions of X
.
References
Agenbag, J.J., A.J. Richardson, H. Demarcq, P. Freon, S. Weeks, and F.A. Shillington. "Estimating Environmental Preferences of South African Pelagic Fish Species Using Catch Size- and Remote Sensing Data". Progress in Oceanography 59, No 2-3 (October 2003): 275-300. (doi:10.1016/j.pocean.2003.07.004).
Examples
data(wbImage)
# Agenbag, method 1
agenbag1 <- agenbagFilters(X = wbImage, algorithm = 1)
# Agenbag, method 2
agenbag2 <- agenbagFilters(X = wbImage, algorithm = 2)
# Plotting results
par(mfrow = c(3, 1), mar = rep(0, 4))
# Original
image(wbImage, axes = FALSE, col = gray.colors(n = 1e3))
# Calculated
cols <- hcl.colors(n = 1e3, palette = "YlOrRd", rev = TRUE)
image(agenbag1, axes = FALSE, col = cols)
image(agenbag2, axes = FALSE, col = cols)