* join regions that are close together
* @param rs
*/
protected void join(ArrayList<Region> rs){
for( int i=0; i<rs.size()-1; i++ ){
Region r= (Region)rs.get(i);
Region rn= (Region)rs.get(i+1);
if(rn.higherThan(r)){
double dis= rn.low-r.high;
if(dis<=par.joinGap){
try{
Region ovl= new Region(r.low, rn.high);
rs.set(i, ovl);
rs.remove(rn);
i--;
}catch(RegionException re){
re.printStackTrace();