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Extract exposure values to features

Source: R/fire_exp_extract.R
fire_exp_extract.Rd

fire_exp_extract() extracts the underlying exposure value for each feature in the values layer.

Usage

fire_exp_extract(exposure, values)

Arguments

exposure

SpatRaster (e.g. from fire_exp())

values

Spatvector of points or polygons

Value

a SpatVector object with new attribute(s)

Details

This function appends the underlying exposure value to the input feature as a new attribute. The values input can be provided as either points or polygons. The values should be singlepart features (i.e. the attribute table has one row per value). If the values are polygon features both the maximum and mean exposure is computed. Any values outside the extent of the exposure raster will be returned with an exposure of NA.

Outputs from this function can be visualized with fire_exp_extract_vis() or exported as a spatial feature.

Spatial Reference

The inputs for the exposure and values layer must have the same coordinate reference system (CRS) defined. The transects will be returned in the same CRS as the inputs.

Scale

The spatial resolution of the input exposure raster will effect the output. The exposure value returned by this function are based on the cell value underlying the feature in the values input. Note that if the resolution of the exposure raster is coarse, there may be multiple values within the same cell and the returned values will reflect this. For polygon features, the maximum and mean value of all cells within the boundary of the polygon are used. If the exposure raster is coarse, there may not be more than one cell within the polygon which will result in these values being the same.

Examples

# read example hazard data
hazard_file_path <- "extdata/hazard.tif"
hazard <- terra::rast(system.file(hazard_file_path, package = "fireexposuR"))

# read example area of interest geometry
geom_file_path <- "extdata/polygon_geometry.csv"
geom <- read.csv(system.file(geom_file_path, package = "fireexposuR"))

# generate an area of interest polygon with the geometry
aoi <- terra::vect(as.matrix(geom), "polygons", crs = hazard)

# generate random points within the aoi polygon
points <- terra::spatSample(aoi, 100)

# compute exposure
exposure <- fire_exp(hazard)

fire_exp_extract(exposure, points)
#>  class       : SpatVector 
#>  geometry    : points 
#>  dimensions  : 100, 1  (geometries, attributes)
#>  extent      : 398037.5, 401850.2, 6048781, 6051320  (xmin, xmax, ymin, ymax)
#>  coord. ref. : NAD83 / Alberta 10-TM (Forest) (EPSG:3400) 
#>  names       : exposure
#>  type        :    <num>
#>  values      :   0.2625
#>                  0.7375
#>                  0.6875