Stitch terrain in unity

TerrainStitcher.cs

class TerrainStitcher extends EditorWindow {
    public var terrain1: Terrain = null;
    public var terrain2: Terrain = null;
    public var options: String[] = ["X", "Z"];
    public var index: int = 0;
 
    @MenuItem ("Tools/Terrain stitcher")
    static function ShowWindow () {
        EditorWindow.GetWindow (TerrainStitcher);
    }
 
 
    function OnGUI () {
        index = EditorGUILayout.Popup("Axis:", index, options);
        terrain1 = EditorGUILayout.ObjectField("Terrain 1:", terrain1, Terrain, true);
        terrain2 = EditorGUILayout.ObjectField("Terrain 2:", terrain2, Terrain, true);
        if (GUILayout.Button("Stitch"))
            Stitch ();
    }
 
    function Stitch () {
        if (!(terrain1 && terrain2)) {
            Debug.LogError("No terrain selected.");
            return;
        }
        var data1 : TerrainData = terrain1.terrainData;
        var data2 : TerrainData = terrain2.terrainData;
       
        if (!(data1.heightmapWidth == data2.heightmapWidth)) {
            Debug.LogError("Width of the terrains must be equal.");
            return;
        }
       
       
        var a : float[,];
        var b : float[,];
        var h : int = data1.heightmapWidth;
        var i : int = 0;
        a = data1.GetHeights(0,0,h,h);
        b = data2.GetHeights(0,0,h,h);
        h-=1;
       
        if (index==0)   //X axis
            for(i = 0; i < h; i++) {
                a[i,h]=(a[i,h]+b[i,0])/2;
                b[i,0]=a[i,h];
            }
        else    //Z axis
            for(i = 0; i <= h; i++) {
                a[h,i]=(a[h,i]+b[0,i])/2;
                b[0,i]=a[h,i];
            }
       
        data1.SetHeights(0,0,a);
        data2.SetHeights(0,0,b);
    }
}