(c) 



FIGURE 7. THE "THREE LEVEL TOLERANCE" ALGORITHM USES A FIRST LEVEL 

 TOLERANCE VALUE, W], TO DETECT "THIN LINE SETS" IN A 

 DIGITAL PROFILE (a). A SECOND LEVEL TOLERANCE VALUE, 

 W2, IS USED TO DETECT "VIRTUALLY COLINEAR" POINTS IN A 

 REGRESSION SET (b). WHEN A VIRTUALLY COLINEAR POINT IS 

 DETECTED A NEW REGRESSION SET IS COMPUTED, COMBINING 

 LINE SETS ON EACH SIDE OF THE COLINEAR POINT. A THIRD 

 TOLERANCE LEVEL VALUE, W3, IS USED TO DETERMINE WHETHER 

 THERE IS A DATA POINT THAT IS AN "INTOLERABLE" DISTANCE 

 FROM THE RESULTING REGRESSION SET (c). 



13 



