Filter positions by an area

Filters out positions lying inside or outside an area. The area can be defined in two ways, either by its x- and y-coordinate ranges, or by an sf-POLYGON object. MULTIPOLYGON objects are supported by the internal function atl_within_polygon.

Usage

atl_filter_bounds(
  data,
  x = "x",
  y = "y",
  x_range = NA,
  y_range = NA,
  sf_polygon = NULL,
  remove_inside = TRUE
)

Arguments

data

A data.table or extension which contains x- and y-coordinates.

x

The x coordinate column.

y

The y coordinate column.

x_range

The range of x coordinates.

y_range

The range of y coordinates.

sf_polygon

sfc_POLYGON object which must have a defined CRS. The polygon CRS is assumed to be appropriate for the positions as well, and is assigned to the coordinates when determining the intersection.

remove_inside

Whether to remove points from within the range. Setting negate = TRUE removes positions within the bounding box specified by the x- and y-ranges.

Value

A data.table of tracking locations with attractor points removed.

Author

Pratik R. Gupte and Johannes Krietsch

Examples

# packages
library(tools4watlas)
library(sf)
library(ggplot2)

# load example data
data <- data_example

# create basemap
bm <- atl_create_bm(data, buffer = 800)

# create a bounding box to filter data
griend_east <- st_sfc(st_point(c(5.275, 53.2523)), crs = st_crs(4326)) |>
  st_transform(crs = st_crs(32631))

# define bbox to crop data
bbox_crop <- atl_bbox(griend_east, asp = "16:9", buffer = 2000)
bbox_sf <- st_as_sfc(bbox_crop) # just for plotting as sf object

# geom_sf overwrites coordinate system, so we need to set the limits again
bbox <- atl_bbox(data, buffer = 800)

# plot points and tracks with standard ggplot colours
bm +
  geom_path(
    data = data, aes(x, y, colour = tag),
    linewidth = 0.5, alpha = 0.1, show.legend = TRUE
  ) +
  geom_point(
    data = data, aes(x, y, colour = tag),
    size = 0.5, alpha = 1, show.legend = TRUE
  ) +
  geom_sf(data = bbox_sf, color = "firebrick", fill = NA) +
  scale_color_discrete(name = paste("N = ", length(unique(data$tag)))) +
  theme(legend.position = "top") +
  # set extend again (overwritten by geom_sf)
  coord_sf(
    xlim = c(bbox["xmin"], bbox["xmax"]),
    ylim = c(bbox["ymin"], bbox["ymax"]), expand = FALSE
  )
#> Coordinate system already present.
#> ℹ Adding new coordinate system, which will replace the existing one.


# filter data with bounding box
# note: when filtering with a rectangle bounding box
# and large datasets, using th range is faster than sf_polygon
data_filtered <- atl_filter_bounds(
  data = data,
  x = "x",
  y = "y",
  x_range = c(bbox_crop["xmin"], bbox_crop["xmax"]),
  y_range = c(bbox_crop["ymin"], bbox_crop["ymax"]),
  remove_inside = FALSE
)

# plot cropped data
bm +
  geom_path(
    data = data_filtered, aes(x, y, colour = tag),
    linewidth = 0.5, alpha = 0.1, show.legend = TRUE
  ) +
  geom_point(
    data = data_filtered, aes(x, y, colour = tag),
    size = 0.5, alpha = 1, show.legend = TRUE
  ) +
  geom_sf(data = bbox_sf, color = "firebrick", fill = NA) +
  scale_color_discrete(name = paste("N = ", length(unique(data$tag)))) +
  theme(legend.position = "top") +
  # set extend again (overwritten by geom_sf)
  coord_sf(
    xlim = c(bbox["xmin"], bbox["xmax"]),
    ylim = c(bbox["ymin"], bbox["ymax"]), expand = FALSE
  )
#> Coordinate system already present.
#> ℹ Adding new coordinate system, which will replace the existing one.