clean_land_points {dafishr}

Clean points falling inland

Description

This functions eliminates points falling inland by using st_difference() function from the sf package.

Usage

clean_land_points(x, mx_inland = mx_inland)

Arguments

x

A data.frame containing latitude and longitude coordinates of vessels tracks to be cleaned by land area

mx_inland

is a shapefile loaded with the packages representing inland Mexico area, it can be uploaded with ⁠data("mx_inland)⁠

Details

Points falling inland in Vessel Monitoring System, VMS, dataset are obvious mistakes, thus need to be eliminated from the data. The function calls a stored shapefile mx_inland which is a custom sf object created using a coastline buffer to avoid eliminating points because of lack of precision within the shapefiles. The function works with any dataset containing coordinate points in crs = 4326 and named latitude and longitude. See first example with a non-VMS dataset. A second example below shows the usage on VMS sample data.

Value

A data.frame object

Warning

This function takes a while!! To test you can use the dplyr::sample_n() function as it is shown in the example.

Examples

# with non VMS data
x <- data.frame(
  longitude = runif(1000, min = -150, max = -80),
  latitude = runif(1000, min = 15, max = 35)
)
data("mx_inland")
x <- clean_land_points(x, mx_inland)

# using sample_dataset

data("sample_dataset", "mx_inland")

vms_cleaned <- vms_clean(sample_dataset)
vms_no_land <- clean_land_points(vms_cleaned, mx_inland)

# You can check the results by plotting the data

vms_cleaned_sf <- sf::st_as_sf(vms_cleaned, coords = c("longitude", "latitude"), crs = 4326)

vms_no_land_sf <- sf::st_as_sf(vms_no_land, coords = c("longitude", "latitude"), crs = 4326)

library(ggplot2)
ggplot(vms_cleaned_sf) +
  geom_sf(col = "red") +
  geom_sf(data = vms_no_land_sf, col = "black")

# in the provided example only few inland points are eliminated.
# There are more evident one within historical data.