Merge pull request #12 from anirudhgovind/dev

add: st_orientation

R/convenience_functions.R

@@ -83,6 +83,47 @@ euclideanDistance <- function (pointA, pointB) {
   sqrt(((pointA[, 1] - pointB[, 1]) ^ 2) + ((pointA[, 2] - pointB[, 2]) ^ 2))
 }
 
+#' Calculate the angle between a line and the horizontal given two
+#' coordinate locations.
+#'
+#' @param x1 the x-coordinate of the first point.
+#' @param y1 the y-coordinate of the first point.
+#' @param x2 the x-coordinate of the second point.
+#' @param y2 the y-coordinate of the second point.
+#'
+#' @return The angle between the line and the horizontal.
+#' @keywords internal
+#' @noRd
+calc_angle <- function(x1,
+                       y1,
+                       x2,
+                       y2) {
+
+  # Get the height
+
+  height <- abs(y2 - y1)
+
+  # Get the base
+
+  base <- abs(x2 - x1)
+
+  # Get the angle
+
+  angle <- round(rad_to_deg(atan(height/base)),
+                 3)
+}
+
+#' Convert an angle in radians to degrees.
+#'
+#' @param radians the angle in radians.
+#'
+#' @return The angle in degrees.
+#' @keywords internal
+#' @noRd
+rad_to_deg <- function(radians) {
+  return(radians * 180 / pi)
+}
+
 #' Add a unique identifier to each observation.
 #'
 #' @param x a `sf` object with geometries.

R/st_nest_coordinates.R

@@ -0,0 +1,114 @@
+#' Nest `POINT` geometries to `LINESTRING`
+#'
+#' @param x a `df` containing coordinates in columns named `x1`, `y1`, `x2`,
+#' and `y2`.
+#'
+#' @return A `sf` object containing `LINESTRING` geometries **without** a CRS.
+#' @export
+#'
+#' @examples
+st_nest_coordinates <- function(x) {
+
+  # Housekeeping
+
+  x1 <- y1 <- x2 <- y2 <- NULL
+
+  # If cols are present in the data run the following:
+
+  if (any(c("x1", "y1", "x2", "y2") %in% colnames(x))) {
+    # Keep other columns
+
+    x_other <- x |>
+      dplyr::select(-x1,
+                    -y1,
+                    -x2,
+                    -y2)
+
+    # Convert to an sf object
+
+    x_nested <- sf::st_sf(data.frame(geometry = sf::st_as_sfc(
+      paste0("LINESTRING (",
+             x$x1,
+             " ",
+             x$y1,
+             ", ",
+             x$x2,
+             " ",
+             x$y2,
+             ")")
+    )))
+
+    # Add the other columns back in
+
+    x_nested <- cbind(x_nested,
+                      x_other)
+
+    return(x_nested)
+
+  } else {
+    stop("Coordinates must be provided in columns x1, y1, x2, and y2.")
+  }
+
+}
+
+
+#' Unnest `POINT` geometries from `LINESTRINGS`
+#'
+#' @param x a `sf` object containing `LINESTRING` geometries.
+#'
+#' @return A `df` where each row contains the `x1`, `y1`, `x2`, and `y2`
+#' coordinates for a line.
+#'
+#' @export
+#'
+#' @examples
+st_unnest_coordinates <- function(x) {
+
+  # Housekeeping
+
+  id <- temp_id <-  x1 <- y1 <- x2 <- y2 <- NULL
+
+  # Check types and convert to linestrings.
+
+  x_lines <- process_linestrings(x)
+
+  # Keep other columns
+
+  x_other <- x |>
+    add_unique_id() |>
+    sf::st_set_geometry(NULL)
+
+  # Get coordinates
+
+  x_coords <- as.data.frame(sf::st_coordinates(x_lines))
+
+  # Set colnames
+
+  colnames(x_coords) <- c("x1", "y1", "id")
+
+  # Group by id. Mutate x2 and y2 as lead values.
+  # This should result in a number of NAs.
+  # Drop them.
+
+  # Add x2 and y2
+
+  x_coords <- x_coords |>
+    dplyr::group_by(id) |>
+    dplyr::mutate(x2 = dplyr::lead(x1,
+                                   n = 1,
+                                   order_by = id),
+                  y2 = dplyr::lead(y1,
+                                   n = 1,
+                                   order_by = id)) |>
+    dplyr::ungroup() |>
+    stats::na.omit()
+
+  # Add other columns
+
+  x_coords <- dplyr::left_join(x_coords,
+                               x_other,
+                               by = c("id" = "temp_id")) |>
+    dplyr::select(-id)
+
+  return(x_coords)
+}

R/st_orientation.R

@@ -0,0 +1,56 @@
+#' Determine the interior angle between a `LINESTRING` and the horizontal.
+#'
+#' @param x a `sf` object containing `LINESTRING` geometries.
+#'
+#' @return An unnested `sf` object containing the orientation of each line
+#' segment making up the original `LINESTRING` geometries.
+#' @export
+#'
+#' @examples
+st_orientation <- function(x) {
+
+  # Housekeeping
+
+  id <- x1 <- y1 <- x2 <- y2 <- NULL
+
+  # Keep track of the crs
+
+  x_crs <- sf::st_crs(x)
+
+  # The extract coordinates function adds columns titled x1, y1, x2, and y2
+  # It then computes the angles of each line string.
+
+  x_orientation <- st_unnest_coordinates(x) |>
+    dplyr::mutate(
+      orientation = dplyr::case_when(
+        x2 > x1 & y2 < y1 ~ -calc_angle(x1,
+                                        y1,
+                                        x2,
+                                        y2),
+        x2 < x1 &
+          y2 > y1 ~ -calc_angle(x1,
+                                y1,
+                                x2,
+                                y2),
+        y2 == y1 ~ 0,
+        x2 == x1 ~ 90,
+        TRUE ~ calc_angle(x1,
+                          y1,
+                          x2,
+                          y2)
+      )
+    )
+
+  # Nest the columns to form line strings
+
+  x_orientation <- st_nest_coordinates(x_orientation)
+
+  # Add the crs back in
+
+  sf::st_crs(x_orientation) <- x_crs
+
+  return(x_orientation)
+
+}
+
+

_pkgdown.yml

@@ -22,6 +22,7 @@ reference:
   contents:
   - add_unique_id
   - st_merge_spatialunits
+  - st_orientation
   - st_survey_spatialunits
 
 - subtitle: Datasets