# inla.nonconvex.hull: Nonconvex set extensions. In andrewzm/INLA: Functions which allow to perform full Bayesian analysis of latent Gaussian models using Integrated Nested Laplace Approximaxion

## Description

Constructs a nonconvex boundary for a point set using morphological operations.

## Usage

 ``` 1 2 3 4 5 6 7 8 9 10``` ```inla.nonconvex.hull(points, convex = -0.15, concave = convex, resolution = 40, eps = NULL) inla.nonconvex.hull.basic(points, convex = -0.15, resolution = 40, eps = NULL) ```

## Arguments

 `points` 2D point coordinates (2-column matrix). `convex` The desired extension radius. Also determines the smallest allowed convex curvature radius. Negative values are interpreted as fractions of the approximate initial set diameter. `concave` The desired minimal concave curvature radius. Default is `concave=convex`. `resolution` The internal computation resolution. A warning will be issued when this needs to be increased for higher accuracy, with the required resolution stated. `eps` The polygonal curve simplification tolerance used for simplifying the resulting boundary curve. See `inla.simplify.curve` for details.

## Details

Morphological dilation by `convex`, followed by closing by `concave`, with minimum concave curvature radius `concave`. If the dilated set has no gaps of width between

2*convex*(sqrt(1+2*concave/convex) - 1)

and 2*concave, then the minimum convex curvature radius is `convex`. Special case `concave=0` delegates to `inla.nonconvex.hull.basic`

The implementation is based on the identity

dilation(a) & closing(b) = dilation(a+b) & erosion(b)

where all operations are with respect to disks with the specified radii.

## Value

An `inla.mesh.segment` object.

## Note

Requires `nndistF` from the `splancs` package.

## Author(s)

Finn Lindgren finn.lindgren@gmail.com

## Examples

 ```1 2 3 4 5 6``` ```if (require(splancs)) { loc = matrix(runif(20), 10, 2) boundary = inla.nonconvex.hull(loc, convex=0.2) lines(boundary, add=FALSE) points(loc) } ```

andrewzm/INLA documentation built on May 10, 2019, 11:12 a.m.