# Detect Rotating Patterns in Vector Fields Detect patterns in vector fields represented on a grid by looking in the rook's neighbourhood of each grid cell. This function is analogous to `PatternDetect`, except that it detects rotational patterns. Four patterns are detected: clockwise rotation when rotation in all four neighbbour grids appears clockwise, counter clockwise rotation when rotation in all four neighbour grids appears counter-clockwise, and partial clockwise and counter-clockwise rotation, when all but one of the four adjacent neighbour cells has vectors that indicate rotation. For all of the patterns above a sub-pattern is specified as convergence when all of the vectors in the four adjacent grids point towards the focal cell or a divergence when all of the vectors in the four adjacent grids point away from the focal cell. ```r RotationDetect(vfdf) ``` ## Arguments - `vfdf`: A data frame as returned by `DispField`, `DispFieldST`, or `DispFieldSTall` with at least five rows (more is better) ## Returns A data frame as returned by `DispField`, `DispFieldST`, or `DispFieldSTall`, with three additional columns. The first additional column is called Pattern in which the patterns around each focal cell are categorized as clockwise, counter-clockwise, partial clockwise, partial counter-clockwise, or NA. The second additional column, called SubPattern, indicates whether all arrows point towards (convergence) or away (divergence) from the focal cell. The third additional column is called PatternCt, which contains a one if all four neighbourhood grid cells contain displacement estimates, and a NA otherwise. ## Examples ```r # creating rotation patterns Mat1 <- matrix(rep(0,9*9), nrow = 9) Mat1[c(1:3), 4] <- 1 Mat1[c(7:9), 6] <- 1 Mat1[4, c(7:9)] <- 1 Mat1[6, c(1:3)] <- 1 Mat1 Mat2 <- matrix(rep(0,9*9), nrow = 9) Mat2[c(1:3), 5] <- 1 Mat2[c(7:9), 5] <- 1 Mat2[5, c(7:9)] <- 1 Mat2[5, c(1:3)] <- 1 Mat2 # rasterizing rast1 <- terra::rast(Mat1) terra::plot(rast1) rast2 <- terra::rast(Mat2) terra::plot(rast2) # Detecting clockwise rotation (VFdf1 <- DispField(rast1, rast2, factv1 = 3, facth1 = 3, restricted = TRUE)) (patdf1 <- RotationDetect(VFdf1)) # Detecting counter-clockwise rotation (VFdf2 <- DispField(rast2, rast1, factv1 = 3, facth1 = 3, restricted = TRUE)) (patdf2 <- RotationDetect(VFdf2)) ```

RotationDetect function