Ops.focal_special: Custom spatial filtering for image

Description Usage Arguments Details Value Warning Author(s) References See Also Examples

Description

For each band and for each cell, function calculates value using specific matrix of square window. Focal operation of map algebra.

Usage

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focal_special(x, type = c("custom", "gaussian", "laplacian", "osisaf",
                          "hires", "correl", "LoG", "sobel", "sobelG"),
             fmask = NULL, size = 3, alpha = 0.5, sigma = (size-1)/4,
             cover = 1 - 1e-06, fillNA = FALSE, saveMargin = FALSE, verbose = 0L)

Arguments

x

Object of class ursaRaster.

type

Character, which is checked by match.arg.

fmask

Numeric square matrix. Filter mask. If NULL then matrix(1,ncol=1) is used. Default is NULL.

size

Numeric. Diameter of circuled filter mask. Coerced to the nearest odd value not less than original value.

alpha

Nimeric. Parameter alpha for "Laplacian", "LoG", "hires", "correl" filters. Ignored for others. Default is 0.5.

sigma

Numeric. Parameter sigma for "Gaussian", "LoG" filters. Ignored for others. Default is 0.5.

cover

Numeric. 0<=cover<=1. Quota for NA values in the focal window in relation to the squared size of the focal window. Quota exceeding leads to recording NA value in the cell. Default is cover=1-1e-6.

fillNA

Logical. If TRUE then only NA values of source image can be changed, and non-NA values of source image are kept without changes. It may provide less reducing of spatial resolution in the task of spatial interpolation. Default is FALSE.

saveMargin

Logical. If TRUE then adaptive window size is used for cells, where original window goes over image boundary. If FALSE then image is expanded to the half size of focal window by NA values and argument cover is applied to this expanded part. Default is FALSE.

verbose

Integer of 0L, 1L, or 2L, or logical, which is coerced to integer. The level of verbosity. Values >0 provide some additional information on console, verbose=1L is less detailed, verbose=2L is more detailed. Default is 0L.

Details

Developed under impression from Matlab's "fspecial".

Value

Object of class ursaRaster with the same number of bands as in input raster.

Warning

Laplacian of Gaussian filter (type="LoG") is not implemented clearly due to applying continuous-valued formula to discrete matrix.

Author(s)

Nikita Platonov platonov@sevin.ru

References

TODO(pl): at least reference to 'osisaf'.

See Also

Other focal operations: focal_mean, focal_median, focal_extrem.

Examples

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session_grid(NULL)
v <- round(runif(8,min=-1,max=1),3)
customFilter <- matrix(c(v[1:4],-sum(v),v[5:8]),ncol=3)
a <- ursa_dummy(1,mul=4/8,elements=32)
tpList <- eval(formals("focal_special")$type)
res <- c(src=a,as.ursa(bandname=tpList))
for (tp in tpList) {
   message(tp)
   res[tp] <- focal_special(a,tp,fmask=customFilter,size=11,sigma=1,alpha=0.8
                           ,saveMargin=0,verbose=2L)
}
print(res)
display(res,decor=FALSE)

ursa documentation built on Jan. 25, 2022, 5:08 p.m.