# sl.mhd.edge: Edge Calculator for Modified Hausdorff Distance In helgegoessling/spheRlab: Spherical Geometry, Analysis, and Plotting of Geoscientific Data on Arbitrary Grids

## Description

This function provides the (lon,lat) coordinates of an edge (e.g. sea ice edge) and of its land-ice interface, given a threshold value.

## Usage

 `1` ```sl.mhd.edge(Var,LonGrid,LatGrid,Threshold) ```

## Arguments

 `Var` The variable from which the edge has to be extracted. For sea ice this can be sea ice concentration or sea ice probability. Generally this is a 2D `M x N` array. In case of a model output with more than one ensemble member, this parameter can be passed as 3D `M x N x e` array, with `e` as the ensemble size. In this case the sea ice edge is calculated using the sea ice probability. IMPORTANT: Apply a data land mask as NaN directly to `Var` before passing the argument to the function. In this way the calculation of MHD will be meaningful. `LonGrid` The `M x N` longitude grid. See the function `sl.ll.rec` for more details. `LatGrid` The `M x N` latitude grid. See the function `sl.ll.rec` for more details. `Threshold` A threshold value (number). For sea ice concentration this is usually 15 %

## Details

Please refer to the function `sl.mhd.edge` to calculate the coordinates of the edge and of the land interface. `sl.mhd.edge` output is the natural imput for `sl.mhd`. The distance employed to compute the MHD is the "great circle distance", given by `sl.gc.dist`.

## Value

A list containing the (lon,lat) coordinates of the edge and of the land-ice interface.

## Author(s)

Lorenzo Zampieri

`sl.mhd`
 ```1 2 3``` ```list = sl.mhd.edge(SeaIceConcentration,LonGrid,LatGrid,Threshold) ## sl.mhd(Edge1,Edge2,LandEdge1,LandEdge2) ## Should result in double, which represent the MHD of the two edges in meters ```