function  getM(coord,cornerA,cornerB){  

    // find membership of coord in cornerA  
    // (distance from opposite corner) / (distance between cornerA and cornerB)  
    var m = 1.0;  
    var dm =  getDistance(cornerA,cornerB); // maximum distance  

    var d =  getDistance(coord,cornerA); // dist between point and corner  

    if(dm == d){ return 0;} // if equal then point is maximum distance from corner and has no membership  
    // need the smaller part of the distance so need to flip  
    d = dm-d;  
    m = d / dm;  
    return m;  
  }