Area of forest change

Calculates the changes in forest area based on a rasterObject forest mask and a SpatialPolygonsDataFrame containing areas of interest.

Usage

AreaCalc(
  inputForestMap = NULL,
  studysite = NULL,
  latlon = NULL,
  polyName = NULL,
  ncores = 1,
  saveCSV = FALSE,
  years = 2001:2018
)

Arguments

inputForestMap

A RasterLayer object with forest cover represented in binary (e.g 0 represents no forest; 1 represents forest). Each layer is expected to represent one year in the years object in a consecutive order.

studysite

An object of type sf with a given number of polygons defining the areas of interest. Forest area statistics will be calculated for features in the studysite object.

latlon

logical: Indicates whether or not the inputForestMap object is based on a geographic coordinate system or is projected to a planar coordinate system. In the former case, area is approximated by raster::area.

polyName

charachter of length 1. Indicates the column in the data frame of the studysite object to uniquely identify the features of interest. The function will fail if there is no unique identification of the polygons

ncores

The number of cores to use, i.e. at most how many child processes will be run simultaneously.

saveCSV

Default is FALSE. You can specify a directory on your local machine where the results area saved in .csv format. The features will be identified by the column specified in polyName.

years

A vector of type numeric indicating the years which are represented by pixels. For GFW data and the default these are 2001 to 2018.

Value

The studysite object with its data frame appended columnwise for every single entry in the years object representing the total area of forest in a given layer of the inputForestMap object. If latlon=TRUE the returned area is in km², otherwise in the squared unit of the input projection (most commonly in meters).

Note

This function relies heavily on parallization, indicating the importance of both, a high number of CPUs and large enough RAM.

Author

Darius Görgen (MapTailor Geospatial Consulting GbR) info@maptailor.net
Maintainer: MAPME-Initiative contact@mapme-initiative.org
Contact Person: Dr. Johannes Schielein
Copyright: MAPME-Initiative
License: GPL-3

Examples

library(sf)
#> Linking to GEOS 3.8.0, GDAL 3.0.4, PROJ 6.3.1; sf_use_s2() is TRUE
library(raster)
#> Loading required package: sp
library(mapme.forest)

aoi = st_read(system.file("extdata", "aoi_polys.gpkg", package = "mapme.forest"))
#> Reading layer `aoi_polys' from data source 
#>   `/home/runner/work/_temp/Library/mapme.forest/extdata/aoi_polys.gpkg' 
#>   using driver `GPKG'
#> Simple feature collection with 8 features and 1 field
#> Geometry type: POLYGON
#> Dimension:     XY
#> Bounding box:  xmin: 107.1291 ymin: 16.59741 xmax: 107.2502 ymax: 16.6916
#> Geodetic CRS:  WGS 84
yearlyRaster = stack(system.file("extdata", "pkgTest_yearlyCover.tif",
                                 package = "mapme.forest"))
result = AreaCalc(inputForestMap = yearlyRaster,
                  studysite = aoi[1,],
                  latlon = TRUE,
                  polyName = "id",
                  ncores = 1,
                  saveCSV = FALSE,
                  years = 2000:2018)
str(result)
#> Classes ‘sf’ and 'data.frame':	1 obs. of  21 variables:
#>  $ id       : int 1
#>  $ area_2000: num 0.722
#>  $ area_2001: num 0.722
#>  $ area_2002: num 0.722
#>  $ area_2003: num 0.722
#>  $ area_2004: num 0.721
#>  $ area_2005: num 0.491
#>  $ area_2006: num 0.135
#>  $ area_2007: num 0.135
#>  $ area_2008: num 0.129
#>  $ area_2009: num 0.128
#>  $ area_2010: num 0.128
#>  $ area_2011: num 0.128
#>  $ area_2012: num 0.0685
#>  $ area_2013: num 0.0371
#>  $ area_2014: num 0.0275
#>  $ area_2015: num 0.0264
#>  $ area_2016: num 0.0257
#>  $ area_2017: num 0.0257
#>  $ area_2018: num 0.0257
#>  $ geom     :sfc_POLYGON of length 1; first list element: List of 1
#>   ..$ : num [1:5, 1:2] 107 107 107 107 107 ...
#>   ..- attr(*, "class")= chr [1:3] "XY" "POLYGON" "sfg"
#>  - attr(*, "sf_column")= chr "geom"
#>  - attr(*, "agr")= Factor w/ 3 levels "constant","aggregate",..: NA NA NA NA NA NA NA NA NA NA ...
#>   ..- attr(*, "names")= chr [1:20] "id" "area_2000" "area_2001" "area_2002" ...