PixelCt: Count populated pixels in a raster stack

In ICvectorfields: Vector Fields from Spatial Time Series of Population Abundance

Count populated pixels in a raster stack

Description

In order to produce reliable results, the cross-covariance approach implemented in DispField. DispFieldST, and DispFieldSTall needs a certain minimum number of non-zero or non-NA valued pixels in pairs of images or pairs of arrays derived from a raster stack that it uses to compute cross-covariance. The user may define a threshold such as ten percent of the pixels within each sub-grid. This function allows the user to assess whether the minimum threshold number of non-zero pixels per sub-grid are surpassed by returning the number of non-zero pixels within each sub-grid over all of the time instances in the user-supplied raster stack. The user may choose to disregard or mistrust displacement or velocity estimates derived from sub-grids with insufficient numbers of non-zero pixels. This function is designed to be called before or after one of the functions referenced above in order to enable the user to quantify their confidence in displacement or velocity estimates.

Usage

PixelCt(inputstack1, factv1, facth1)

Arguments

inputstack1	a raster stack with each raster layer representing an instance of time. The raster stack should be organized such that the first raster in the stack is the first observed spatial dataset and time progresses forward with the third dimension index of the raster stack. The raster stack should contain only numeric values. Any NA value will be converted to a zero
factv1	an odd integer for the vertical dimension of subgrids
facth1	an odd integer for the horizontal dimension of subgrids

Value

A data frame is returned with the following column names: rowcent, colcent, frowmin, frowmax, fcolmin, fcolmax, and PixelCt. The rowcent and colcent column names are the row and column indices for the center of each sub-grid; frowmin and frowmax are the sub-grid minimum and maximum row indices; fcolmin and fcolmax are the sub-grid minimum and maximum column indices; pixelct is the count of non-zero pixels in the sub-grid over the entire time period covered by the input raster stack.

Examples

# below the example in the DispField function documentation is reproduced
(Mat1 <- matrix(rep(c(1:5, 0, 0, 0, 0), 9), nrow = 9, byrow = TRUE))
(Mat2 <- matrix(rep(c(0, 1:5, 0, 0, 0), 9), nrow = 9, byrow = TRUE))

# Note that rasterizing a matrix causes it to be rotated 90 degrees.
# Therefore, any shift in the x direction is in fact now a shift in the y direction
rast1 <- terra::rast(Mat1)
terra::plot(rast1)
rast2 <- terra::rast(Mat2)
terra::plot(rast2)

(Confdf1 <- PixelCt(c(rast1, rast2), factv1 = 9, facth1 = 9))
# This should return a pixel count of 54: This is the number
# of pixels that were occupied in either the first or second
# time instance.

ICvectorfields documentation built on March 18, 2022, 7:34 p.m.