extract_values: Extract values of indicators

In WCS-Marine/local-reef-pressures: Analysis of local human pressures on tropical coral reefs

Description

Extract values of indicators

Usage

extract_values(data, allreefs, max.radius = 5000)

Arguments

data	Dataframe containing the coordinates of the points to extract values for. It must be a four-column dataframe. The 1st and 2nd columns are ignored by the function; they can contain the region name and the site name, for example. Longitude must be on the 3rd column and latitude on the 4th column.
allreefs	Object of type sp::SpatialPolygonsDataFrame or sf::sf containing polygons for all reefs with values for all indicators.
max.radius	Maximum radius (in meters) to search for nearest polygons. See details.

Details

The function will first transform the input coordinates into the same coordinate reference system of the allreefs object, which follows a WGS84 Pacific-centered reference system (EPSG code: 3832). For each input point, it will then search for the nearest centroid of the polygons of allreefs and assign it the values of the indicators. The search for the nearest centroid is performed over a circle of radius max.radius, expressed in meters. The default value for max.radius, 5000 meters, reflects the size of the polygons of allreefs (0.05 degrees, which is approximately 5 km). If no reef polygon centroid is found within a circle of radius max.radius centered on the input point, the funciton will return NA for that input point. Increasing max.radius can extend the search to reef polygons located farther away.

Value

A dataframe. The first four columns are the same as in data, and the following columns contain the values of the indicators

Examples

# Create dataframe of sampling points
data <- data.frame(
  country = NA,
  name = NA,
  lon = c(47.7, 48, 48.2),
  lat = c(-13.9, -13.5, -13.3)
)
# Load allreefs data
data(allreefs)
# Extract the values of the indicators
extract_values(data, allreefs)

WCS-Marine/local-reef-pressures documentation built on Feb. 13, 2022, 9:26 a.m.