MAPI_GridAuto {mapi}

Function MAPI_GridAuto

Description

Wrapper that computes cell halfwidth for a given beta value, and then builds a grid of hexagonal cells (call to MAPI_GridHexagonal).

Usage

MAPI_GridAuto(samples, crs, beta = 0.25, buf = 0)

Arguments

samples

a data.frame with names and geographical coordinates of samples. Column names must be: 'ind', 'x', 'y'. Optional column 'errRad' with an error radius for sample locations (eg. GPS uncertainty). Coordinates must be projected (not latitude/longitude).

crs

coordinate reference system: integer with the EPSG code, or character with proj4string. When using dummy coordinates (eg. simulation output) you may use EPSG:3857 (pseudo-Mercator) for example. This allows computation but, of course, has no geographical meaning.

beta

A value depending on sampling regularity: 0.5 for regular sampling, 0.25 for random sampling (Hengl, 2006).

buf

optional. This parameter allows to expand or shrink the grid by a number of units in the same reference system as the sample geographical coordinates (0 by default).

Details

The halfwidth cell value used to build the grid is computed as h_w = \frac{\beta \sqrt{A/N}}{\sqrt{2.5980}}, where A is the study area (convex hull of sampling points) and N the number of samples. Parameter beta allows to respect the Nyquist-Shannon sampling theorem depending on sampling regularity (call to MAPI_EstimateHalfwidth).

Value

a spatial object of class 'sf' including the x and y coordinates of cell centers, cell geometry (polygons) and cell id (gid).

Examples

data("samples")
grid <- MAPI_GridAuto(samples, crs=3857, beta=0.5)