ORIGINAL ARTICLE

Overlap-avoidance algorithm for automatic generationof ship assembly drawings

Won-Sun Ruy • Young-Soon Yang

Received: 30 December 2009 / Accepted: 21 July 2010 / Published online: 28 August 2010

� JASNAOE 2010

Abstract The aim of this paper is to investigate an

overlap avoidance algorithm to improve the readability of

automatically-generated ship assembly drawings. Improved

readability can help designers reduce the necessary man-

hours for completing drawings and can improve the quality

of the drawings produced within the given time. An auto-

mation technique is necessary for reasons of economic

efficiency and to perfect communication between designers

and manufacturers. The overlap-avoidance algorithm used

in this paper maximized the readability of drawings using

optimization techniques such as the Genetic Algorithm

and Simulated Annealing, especially in the field of ship

assembly.

Keywords Automatic drawing generation �Overlap-avoidance algorithm � Assembly drawing

1 Introduction

Until now, almost all manufacturing companies have used

‘‘Drawing Middleware’’ for smooth communication

between designers in the office and manufacturers on the

product line. However, it is not easy for designers to

express all of their content on the limited medium of

drawing paper. Moreover, the content is too huge to be

described exactly in a restricted duration of time. Unfor-

tunately, assembly drawings in the ship-building field are

no exception to this problem. Figure 1 shows the assembly

drawing of a longitudinal bulkhead.

These days, some CAD systems provide us the ability to

automate the drawing process. A typical example is auto-

matic dimensioning [1, 2] based on pre-defined rules and

company drawing standards. Another example is the pro-

cess in which one selects and extracts the sectional view

from the entire product. Guan and Fang [3] tried to remove

the hidden lines of a 3-D product from a 2-D drawing. In

another case, Chen et al. [4] tried to select the necessary

views in an assembly drawing in the mechanical field. In

the field of ship-building, Woo et al. [5] developed an

automatic pipe ISO-Drawing and BOM generation system.

It locates pipe views on the drawings and attaches the

corresponding product information. The resulting pipe

installation drawings require designers to do additional

touch-up work. This paper focuses on the fact that in the

case of the more complicated drawings, most designers

consume their time and effort in adding and relocating the

design descriptions and related symbols on the product

contour, and that related studies and application cases have

not been reported yet in the literature; however, Joseph and

Pridmore [6] presented a methodology for the interpreta-

tion of images of engineering drawings. In this paper, the

authors try to adjust the position of the text and symbols in

order to increase the readability of drawings after the given

algorithm recognizes a drawing.

Various kinds of drawings are required during the

process of ship-building. Okumoto et al. [7] explain the

process in detail and the kinds of drawings used in the field

of ship-building. Among them, the assembly drawing

describes the detail assembly guide on the base of the shell

structure and some outfitting information at various stages

W.-S. Ruy (&)

Daejin University, Sundan, Gyeonggi-do,

Pocheon 487-711, Korea

e-mail: ruy@infoget.co.kr

Y.-S. Yang

Seoul National University, Gwanak-ro, Gwanak-gu,

Seoul 151-742, Korea

e-mail: ysyang@snu.ac.kr

123

J Mar Sci Technol (2010) 15:386–394

DOI 10.1007/s00773-010-0103-0

of the detailed design. To complete an assembly drawing, a

designer should select a compartment and a group of panels

and acquire the view from the CAD system. After that, the

product information of the acquired parts should be placed

at a suitable position. For example, the thick contours on

Fig. 1 are depicted as the structure of the longitudinal

section, and the others describe related information for

assembly and production, with symbols and text which are

comprised of the properties for the elements (plate name,

thickness, bevel value, welding angle, and so on.), fabri-

cation explanations on assembly, and the dimension of the

structures.

The quality of the drawing is the key factor that prevents

errors and communicates the designers’ exact intent to the

site manufacturer. For this, it is significant to note the

following:

1. Standardization of the design properties to be depicted

on the drawings. Unless each designer uses standard-

ized rules to describe product items, the site manufac-

turers might have their own interpretation different

from the designers’ intentions. Therefore, the design-

ers’ group must have a unified standard rule for the

design and product properties description. If the group

has an automatic system generating design and product

properties, this problem can be naturally solved.

2. There are too many kinds of design and product

properties to be described on drawings; even if the

design group has used a fully customized CAD system,

it is impossible for all the different kinds of properties

to be automatically displayed on the screen and placed

at their proper positions. Therefore, designers are

obliged to write the properties themselves. In that case,

there is a strong possibility that the drawing will

contain errors in the written text. The assembly

drawings of ship-building generally have no less than

50 kinds of properties. Table 1 shows representative

properties’ groups which are used to describe an

assembly drawing.

3. Drawing Time DSME annual report (unpublished

outside) said that the time required to complete

assembly drawings takes about 30% of the total time

for detailed ship design, which is comprised of the

modeling, generating all sorts of BOMs and drawings,

and the task of revision. This means that minimizing

the drawing generation time is a key factor in

competitive ship-building.

Fig. 1 An assembly drawing of a longitudinal bulkhead

J Mar Sci Technol (2010) 15:386–394 387

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The contents on a drawing can be classified into 4

groups. One is the contours which represent the product

outlines. The next is the symbols which simply describe

complex objects. The third is the dimensions which depict

the size of the product and its elements. The last is the text

which is used for the detailed explanation of the product.

Depending on the complexity of the product, too many

elements can degrade a drawing’s readability. Generally,

customized CAD locates the properties’ text and symbols

on the representative position of the elements, which can

be the center position of a line or a rectangle. With this

approach, descriptions have no choice but to be attached

and overlap each other. Thus, it has been the designers’

role to arrange the text and symbols of a drawing so it is

easily read by the manufacturers. This job is tedious,

repetitive and time-consuming. However, the real problem

is text and symbols which are not supported by the cus-

tomized CAD system. The designers have no choice but to

bear the burden of supplying the text and symbols based on

their design knowledge and the characteristics of the

elements.

This paper explains an automatic algorithm which can

generate all information without regard to the CAD system

and can arrange all text and symbols so as to avoid each

other using the 2-Dimensional Genetic Algorithm [8, 9],

Simulated Annealing [10], and heuristic methods.

2 Strategy for evaluating the quality of a drawing

To make better drawings, an evaluation strategy should

come before all other considerations. Although there can be

many methods to evaluate a drawing, this paper gets its

idea from graphic image processing and a 2-D individual-

based approach using the Genetic Algorithm.

Figure 2 explains the basic principle for constructing a

data structure describing a drawing’s status. First, a reso-

lution should be decided at which to recognize the drawing.

Table 1 Items in the assembly

drawingProperties Items to be automated

Drawing level Drawing name, drawing form, view arrangement, scale

View level View title, shrinkage, shop fillet air test, hatching region, ruler, detail view

Assembly level Assembly name, section panel

Plate Assembly ID, plate name, thickness, grade, hole dimension, hole name, welding type,

member assembly name

Stiffener Part no., welding angle, welding symbol, molding direction, stiffener dimension, grade,

stiffener type, stiffener end symbol

Others Collar plate symbol and name, thickness difference with adjoin plate, chamfer, various

dimension, welding length

0 0

1 1 0 0

0 1 1 0 0 0 0

0 0 1 1 0 0 0 0 0 1 1

0 1 1 0 1 1 1 0 0

0 0 2 1 1 0

0 0 1 1 0 2 2 0 0

0 0 1 1 0 0 0 0 1 1 0

1 1 0 0 0 0 1 1

0 21

Fig. 2 Basic concept for

evaluating the quality of a

drawing

388 J Mar Sci Technol (2010) 15:386–394

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According to the paper’s resolution, a memory structure is

constructed of cells, each of which is composed of an

unsigned integer. If the elements of a drawing pass by a

grid cells, the relevant grid adds one point. As a matter of

course, a blank cell of the drawing has no point. This

representative method has the merit of easily organizing

the memory structure of the drawing. In addition, running

time can be minimized by choosing the proper resolution.

Above all, this strategy can simply recognize the overlap

status between the elements of the drawing.

However, it is important that the overlap status must be

evaluated from all sides for an exact and practical evalu-

ation of the drawing quality. If a drawing is of sufficient

complexity, the product-contours can be overlapped nor-

mally, and the status data structure cannot be blamed for

incorrect and low-quality drawings. Therefore, the above

mentioned method can be further developed to consider the

unavoidable overlap, avoidable overlap, and impossible

overlap so the evaluation strategy must be expanded as

follows.

For the expanded strategy (see Fig. 3), the contours,

symbols and text must not get the same 1 point. Instead, the

contour gets 1 point and the symbol and text group gets 2

points. This modified strategy changes the evaluation

method of each cell. The unavoidable overlapped cells,

which are composed of two contours, get 2 points and have

no penalty. On the other hand, the avoidable overlapped

cells, which are composed of one contour and a symbol-or-

text, take 3 points and have a relatively small penalty.

However, the impossible-overlapped cells, which are com-

prised of text and symbol, get above 4 points, are mainly

responsible for low-readability, and get the higher penalty.

It is noteworthy that the position of contours and

unmovable symbols (e.g., end symbol of stiffener, collar

plate, etc.) are not variables for the drawing quality but just

constants. Even though there are overlapped cells between

the contour and those symbols, no one can improve the

quality of the drawing for those constants. It is just a

problem of modeling. The key factor for improving the

drawing quality is the position of text and movable sym-

bols whose cells might be imposed by above 4 points. In

the end, the cells evaluated at 3 (movable symbol-text and

contour) and 4 points should be eliminated for better

readability of the drawing.

3 Hierarchical data structure for automation of hull

assembly drawings

Figure 4 shows the hierarchical data structure for a draw-

ing’s recognition. The shadow-line boxes are virtual clas-

ses and specified by the subordinate structure. The filled

boxes are unmovable and constant elements; the white and

black-line boxes are the variables which are the main

elements for the drawing quality and are comprised of

symbols and text.

For example, when the sorts of stiffeners are displayed,

the right-bottom of Fig. 4 shows the traditional drawing

format. Of course, the drawing format can be different

depending on each product field and company. Constant

symbols and contours are not able to move, but the

attached angle, stiffener piece name, and molding direction

should be placed away from the adjacent elements.

4 Arrangement strategy

Globally speaking, the maximum range one variable can

move within a drawing is proportional to the defined reso-

lution of the drawing. However, the detail drawing element’s

position is restricted to its own characteristics. For instance,

the symbols and text of a stiffener should be positioned on the

1-D line or curved line. On the other hand, a plate or panel’s

elements must be located on or near the 2-D in its own region.

2

2

0

4

4

1 1 1

1 1 1

1 1 1

1 1

1 1 1

1

1

1

1

1

1

2

2

1

1

2

4 22 3 2

Empty Region

Forbidden Occupied Region

Allowable Occupied Region

3

Contour

Symbol

Contour+Symbol

Symbol+Symbol

- K2 TB

98

A

31 5 .0 A 3 2

Fig. 3 Concrete concept for

evaluating the quality of a

drawing

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As anticipated, there are too many variables and wide fea-

sible regions on a drawing. One assembly drawing for ship-

building usually has at least 500 variables, and the designer

should carefully consider the relationship between the can-

didate regions of each variable.

In conclusion, this paper suggests two arrangement

strategies for overlap-avoidance, when there are too many

design variables and too many complex rules. The first is

the Knowledge Based Arrangement System (KBAS) which

contains the rules, preference, and alternatives of each

company. Using KBAS, the system specifies the mean-

ingful patterns and converges to the feasible region close to

an exact solution. The second is the Optimization Based

Arrangement System (OBAS), which automates the opti-

mal overlap-avoidance status of the drawing. Table 2

summarizes the roles of KBAS and OBAS, and the 2

chapters below provide more detailed explanations.

4.1 KBAS

To focus on the meaningful design region and accelerate

the arrangement process, the following three rules were

implemented in this paper. These three rules reduce the

design variables and add practical constraints so that the

OBAS can search for a solution within the restricted time.

1. Set the allowable arrangement region of each design

element

Using a heuristic experience-based method, each ele-

ment has the proper constraints and relationship with the

others. For example (see Fig. 5), stiffener name, mold

direction and attach angle, and the related symbol should

be located near its stiffener line. Generally, attach angles

and their symbols move together. Stiffener name and mold

direction also have a pairwise relationship. Surely, this rule

can change depending on the product and the company.

2. Set the arrangement order through the variables’

grouping

Fig. 4 Hierarchical structure of

drawings for avoidance

algorithm

Table 2 Arrangement strategy of ship assembly drawing

KBAS OBAS

1. Candidate space

according to its own

region

1. Representation method: 2-D matrix

chromosome genetic algorithm

2. Preference based

sequential arrangement

3. Construction of various

alternative patterns

2. Searching method: simulated

annealing

Fig. 5 Feasible region and grouping strategy of stiffener’s elements

390 J Mar Sci Technol (2010) 15:386–394

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Without KBAS, it takes 10 min more to get the drawing

solution with a global search algorithm such as SA. Fur-

thermore, the quality of the solution is far from satisfactory

within the restricted time period. Thus, this paper divides the

variables into several groups and applies the OBAS

sequentially for a meaningful solution within the restricted

time period. Here, the sequence order means that the position

of the next groups is determined separately from the

arrangement status of the previous groups. So, the previous

groups have influence on the solution. Its sequence is based

on the designers’ experience.

Table 3 illustrates the four groups of variables for ship

assembly drawings. The 0th group, whose position does not

need to be decided, would be placed at the proper location

without the algorithm. Next, SA is run a total of 3 times com-

pleting the drawing solution. Surely, its drawing is not a strict

solution. If there was plenty of time, SA without KBAS could

search for a more optimal solution. However, this sequential

approach with the designers’ experience can produce a mean-

ingful drawing solution within a restricted time period.

Figure 6 shows the convergence history for the sequential

arrangement strategy. As the SA iteration goes through each

phase, the objective value decreases gradually. Here, the

objective value means the quality of drawings and will be

explained in the next section. Since there are a large number

of important variables in Phase 1, the convergence degree is

steeper than the ones in the other phases.

3. Set the patterns

Generally, each product-manufacturer has unique pat-

terns or rules for drawing descriptions. To generate the

patterns, several properties constitute the one pattern and

act as the role of one variable. This approach has the merit

of reducing the variables and the design domain (Fig. 7).

Even plate is mainly expressed by using the pattern T1;

the patterns T2 and T3 can be used when the allowed space

is too narrow and already occupied by the other properties.

However, if possible, T1 is highly recommended for its

clearance and tradition. T3 on the plate pattern has a

direction line; using T3 should be minimized. The stiffener

and hole pattern is not different from the plate pattern.

4.2 OBAS (fitness function)

The search method description is not a matter of interest in

this paper. Instead, this paper sets the focus on the fitness

function which is composed of four functions as shown in

Table 3 Sequential arrangement strategy of a ship assembly drawing

Arrangement

sequence

Relevant entities

Phase 0th Title, collar plate, assembly name, shrinkage (not

by algorithm)

Phase 1st Stiffener, flange, bracket, neighbor plate thickness,

sub-assembly name

Phase 2nd Block seam symbol, seam bevel, thickness

difference

Phase 3rd Plate description, water air tight information

Fig. 6 Convergence history for the sequential arrangement strategy

Fig. 7 Patterns of each drawing

of design

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Table 4. It is an interesting fact that each function of fitness

has a different weight-value. The ‘‘No Overlap’’ function is

handled as the most important one, and the lower order

functions have less weight value in sequence of prece-

dence. The second function means that the corresponding

description should be located, to the degree possible, at the

center of the drawing item, and the third function controls

the use of the simple pattern as explained in the previous

chapter. The final function causes the description text to

have a larger size under the allowed size. The formula (1)

is the fitness function as follows.

Fitness Fn ¼ Rwkf k; where; wk is weighting value of fk

ð1ÞThis is not a bin packing searching algorithm [9] which

fills up the given space with arbitrary objects without their

overlap. Instead, this algorithm selects the appropriate

pattern and arranges the elements on the restricted region

for drawing readability.

5 Example of overlap-avoidance algorithm applied

in a ship assembly drawing

The overlap-avoidance algorithm reconstructs the rela-

tionship between the product’s contours and the drawing

elements’ descriptions (texts and symbols). This chapter

explains the detail characteristics of each step and surveys

the effect of the algorithm with an example of a ship

assembly drawing.

Figure 8 shows the memory map of a drawing after

applying the overlap-avoidance algorithm, which has a total

Fig. 8 Example of a drawing’s memory map

Table 4 Elements of fitness function

Fitness function Description Importance

No overlap (f1) Symbol and text must not be overlapped and these layouts get the big penalty in the inevitable case

Center position (f2) If possible place at the center of entities.

Simpler pattern (f3) Each entities should be represented as simple as possible (more typical pattern)

Bigger shape (f4) More bigger text

392 J Mar Sci Technol (2010) 15:386–394

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of (210 9 297)/4 grids on a base of A4 paper. The grid size

is 2 mm 9 2 mm. The white space in Fig. 8 means that

there is nothing; the slim width contours (product line) have

a score of 1, and the filled squares have a score of 2–3.

Almost all of a drawing’s elements (plate, stiffener, bracket,

etc.) have their descriptions by their notes.

On the other hand, Fig. 9 is the final result which is

mapped on the CAD system on the basis of the corre-

sponding memory map. All entities which look like a

meaningless black boxes are implemented by the drawing’s

elements, respectively.

Figure 10 compares the status of the two drawings. The

right side drawing is the result of the avoidance algorithm,

and the left side is the initial status. The initial status

contains the texts and symbols which are supplied by the

CAD system, and the unsupplied entities are automatically

generated on the center position of each one. This example

shows the one panel which is comprised of 2 plates and

numerous section panels cross the example drawing. The

slim ellipses on the ‘‘before’’ status indicate the status of

need-to-improve, whereas all texts and symbols on the

‘‘after’’ status are arranged well. Table 5 shows

the numerical comparison between the before and after.

The number of score-3 and score-4 grids definitely

decreases in the after status.

According to the kinds of drawings, the time con-

sumption of this algorithm can vary over a wide spectrum.

The number of elements on the drawing and the size of the

Fig. 10 The comparison

between before and after the

adaptation of avoidance

algorithm

Fig. 9 Mapping result to

Tribon M3 [11]

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drawing are the main factors which determine the running

time of this algorithm. Table 6 shows the time consumed to

generate drawings of a bulk carrier (24,740 ton).

6 Conclusion

To generate good quality assembly drawings, commonly

practice is to extract the data from the CAD system, select

and arrange the appropriate view, determine the scale, and

finally classify the drawings based on the plan of fabrica-

tion for a ship. The avoidance algorithm described in this

paper should be treated as a primary technique to employ

within the field of drawing automation.

To apply the algorithm effectively, the appropriate

feasible region on the drawing is first located through

KBAS, and the final position is then determined by OBAS

in order to produce a good quality drawing within a

restricted time period. This algorithm can be applied to

ship-assembly drawings, which are well-known in the field

as being complicated. The presented algorithm promises to

maximize the readability of a drawing, to standardize

drawing generation, and to reduce the man-hours necessary

to generate a drawing.

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Table 5 Numerical comparison between before and after

Before After

Score No. of grid Score No. of grid

Score 3 2321 Score 3 124

Score 4 and above 471 Score 4 and above 3

Table 6 Consumption time of the avoidance algorithm

Kinds of drawings No. of elements Running time (s)

Section view 345 161

Elevation view 130 31

Deck view 300 132

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