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e.g.		0									8
0				1	1	1	1	1	1	1	0
				1	1	1	1	1	1	1	0
				1	1	1	1	1	1	1	0
				0	0	0	0	0	0	0	0
4

• Compactness can be a measure of mass distribution,

P2

C = -----

A

where,

C = compactness P = perimeter

A = area

• Another measure of mass distribution is thickness,

Area = 21

Perimeter = 16

x Centroid = 3.5

y Centroid = 1.5

Tmin	Dmin	Tmax	Dmax
	= -----------		= -----------
	A		A

where,

T = thickness

Dmin/Dmax = smallest/largest diameters A = Area

17.10 RECOGNITION

17.10.1 Form Fitting

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• It can sometimes help to relate a shape to some other geometric primitive using compact-

ness, perimeter, area, etc.

-ellipse

-square

-circle

-rectangle

17.10.2 Decision Trees

•In the event that a very limited number of parts is considered, a decision tree can be used. The tree should start with the most significant features first, then eventually make decisions on the least significant. Typical factors considered are,

-area

-hole area

-perimeter

-maximum, minimum and average radius

-compactness

•An example of a decision tree is given below. (Note: this can be easily implemented with ifthen rules or Boolean equations)

Part A

C<10 Dmin<0.1

Part B

Dmin>=0.1

Part C

C>=10

Part D

C>=20 A>=20

Part E

A<20

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Bar Codes

•Bar codes are a common way to encode numbers, and sometimes letters.

•The code is sequential left to right, and is characterized by bars and spaces of varied widths. The bar widths corresponds to a numerical digits. These are then encoded into ASCII characters.

•To remain noise resistant there are unused codes in the numerical sequence. If any value scanned is one of the unused values the scan is determined to be invalid.

•There are different encoding schemes.

Code 39/Codabar - these use bars of two different widths for binary encoding

Code 128 - these use different bar widths uses proportional widths to encode a range of values

UPC (Universal Product Code) - EAN (European Article Numbering) -

• The example below shows how a number is encoded with a bar code.