raster_extract {rSPARCS}

Extract Values from a Raster Map

Description

Crop the raster with the boundary of areas of your interest, and extract the values from the raster to each of these areas.

Usage

raster_extract(rastermap,refmap,ID.var,ID.code,cutpoint)

Arguments

rastermap

a raster map containing the information you need, such as the National Land Cover Database 2011.

refmap

"SpatialPolygonsDataFrame" object. A reference map containing the boundary information of your study areas.

ID.var

the name of variable in the refmap indicating the unique ID for each of your study areas.

ID.code

a character vector containing the unique ID for areas that you want to extract the values to. ID.code=ALL" by default where all areas in the reference map are of interest.

cutpoint

a number to dichotomize the values in the raster; specified ONLY when those values are continuous.

Details

Usually for extracting data which are available as rasters such as the land coverage or land usage data.

Value

ID.code

the column indicating the unique ID for each area, followed by the number of cells for each category/colour within that area.

Total cells

the total number of cells within each area.

Examples

library(raster)
set.seed(4715)
rast=raster(matrix(rnorm(500),100,100))
extent(rast)=c(50,100,10,60)
crs(rast)=CRS("+proj=longlat +datum=WGS84")

ref=cbind(x=c(60,80,80,70), y=c(20,25,40,30))
p=Polygon(ref)
ps=Polygons(list(p),ID="ID")
ref=SpatialPolygons(list(ps))
data=data.frame(value=1, ID="10086",row.names="ID")
ref=SpatialPolygonsDataFrame(ref,data)
proj4string(ref)=CRS("+proj=longlat +datum=WGS84")

raster_extract(rastermap=rast,refmap=ref,ID.var="ID",ID.code="ALL",cutpoint=0.5)