R: Function MAPI_EstimateHalfwidth

MAPI_EstimateHalfwidth {mapi} | R Documentation

## Function MAPI_EstimateHalfwidth

### Description

This function computes the side length (= halfwidth) of the hexagonal cells. Halfwidth value can be further used to build a MAPI grid.

### Usage

    MAPI_EstimateHalfwidth(samples, crs, beta = 0.25)

### 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. The coordinates system must be a projection, not latitude/longitude.
`beta` | A value depending on spatial regularity of sampling: 0.5 for regular sampling, 0.25 for random sampling (Hengl, 2006).

### Details

hw = p / sqrt(2.5980) with p = beta * sqrt(A/N), 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.

### Value

halfwidth cell value (side length of hexagonal cells).

### References

Hengl, T. (2006) Finding the right pixel size. Computers & Geosciences, 32, 1283–1298.

### Examples

    data(samples)
    # Computes hexagonal cell halfwidth for the 'samples' dataset using beta=0.5
    hw <- MAPI_EstimateHalfwidth(samples, beta=0.5)

[Package mapi version 1.0.5 Index]