sample_treeline {ElevDistr}

Compute the local treeline

Description

Calculate horizontal and vertical lines between two different classified points from the df input. If used in the context of the treeline: when a point above the treeline (TRUE) and a point below the treeline (FALSE) lie next to each other, the start and the end of the line is calculated and stored. This data point collection represents the local treeline. It is highly recommended to use this function only in combination with generate_grid and classify_above_treeline. The coordinates in the df can only be meaningfully processed if they have the same order and structure as results from generate_grid.

Usage

sample_treeline(df, lonLength, latLength, stepSize = 0.0025)

Arguments

df

Data frame generated by the function classify_above_treeline and therefore containing: longitude, latitude (WGS 84), growing season temperature, growing season length, and a boolean. Longitude and latitude must be of the data type "numeric" and finite. For the boolean TRUE, FALSE and NA is allowed and nothing else.

lonLength

Vector containing the length of the longitudinal sequence. One value, data type "numeric". This information is part of the generate_grid output. One value, data type "numeric" and finite.

latLength

Vector containing the length of the latitudinal sequence. One value, data type "numeric". This information is part of the generate_grid output. One value, data type "numeric" and finite.

stepSize

Step size for the square sampling (in degree). One value, data type "numeric". This stepSize must be identical with the stepSize used in the function generate_grid. It is used to calculate the center between two grid points. One value, data type "numeric" and finite.

Value

A data frame containing line-shaped polygons. Each row containing: a identifier, a start latitude and longitude, a end latitude and longitude.

Author(s)

Livio Bätscher, Jurriaan M. de Vos

Examples

#Recommended usage
temp <- generate_grid(lon = 8.728898, lat = 46.93756, squareSize = 10, stepSize = 0.0025)

gstURL <- paste0("https://os.zhdk.cloud.switch.ch/envicloud/chelsa/chelsa_V2/",
                 "GLOBAL/climatologies/1981-2010/bio/CHELSA_gst_1981-2010_V.2.1.tif")
gslURL <- paste0("https://os.zhdk.cloud.switch.ch/envicloud/chelsa/chelsa_V2/",
                 "GLOBAL/climatologies/1981-2010/bio/CHELSA_gsl_1981-2010_V.2.1.tif")

gst <- terra::rast(gstURL, vsi = TRUE)
gsl <- terra::rast(gslURL, vsi = TRUE)

temp$df <- classify_above_treeline(coords = temp$df, gstRaster = gst, gslRaster = gsl)

treeline <- sample_treeline(df = temp$df, lonLength = temp$lonLength,
                            latLength = temp$latLength, stepSize = 0.0025)