International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 4

Number 1

March 2010

1 INSTRUCTION

With the fast development of water transportation in

recent years, significant projects of harbour and wa-

terway increase constantly, and the traffic density in

water areas also increases unceasingly. Usually the

investments of many harbour projects are enormous

and it was costly if some design mistakes could not

be identified. Once the accident happens, the direct

and indirect losses are inestimable. Hence, it is im-

portant to carry out the assessment of Navigational

Safety in harbour and waterway design to ensure

safety of navigation when the projects are imple-

mented (Guan et al. 2005).

To assess the navigational safety of designing

projects of harbour and waterway, ship-handling

simulator is employed to carry out simulated tests in

real time. Results retrieved from analysis of the test

data are benefit not only for the navigational safety

of the vessel, but also harbour and waterway facili-

ties. The tests help reduce the expenses of the engi-

neering experiment, and optimize the design of the

project. The shiphandling simulator assessment can

improve the economic benefits and competitiveness

of the port. It can check out the potential capacity of

the port and berths, and provide approaches to make

fully use of the berthing ability of the port.

The research work in this paper is partially sponsored by the

Shanghai Leading Academic Discipline Project (grant number:

S30602), and the Natural Science Foundation of China (grant

number: 40801174).

Usually the fast simulation of navigation is

adopted, using the simulation system of two-

dimensional (2D) display. The system is composed

of the Electronic Chart Display and Information Sys-

tem (ECDIS) and the navigational Simulation Con-

trolling System. The operator, who is shown a 2D

chart display, use the keyboard to control the engine

and the rudder. Multiple PC systems can be used

carry out simulation tests of different operation

mode at the same time to accelerate the assessment

procedure.

In order to perform the simulation test described

above, it is a very important step to generate the

ENC data for the planning harbour and waterways.

In this paper, approaches are studied to use various

existing chart data sources and design data of har-

bour and waterway projects. A rational and fast

method is developed for the generation of ENC data

specifically for the assessment of navigational safety

of harbour and waterways.

2 THE NEEDS OF ENC DATA IN NAVIGA-

TIONAL ASSESSMENT

The work of the assessment of navigational safety in

the harbour and waterway design include mainly:

1 Assessing the efficiency of navigation in the

channel. The data, such as the channel width, wa-

ter depth, navigational marks, etc. of the design

waterway, are checked whether the requirements

could be met for the navigational safety of the

Generation of Electronic Nautical Chart Data

for Assessment of Navigational Safety in

Harbour and Waterway Design

K. Guan, C. Shi, S. Wu & T. Xu

Merchant Marine College, Shanghai Maritime University, Shanghai, China

ABSTRACT: Navigational simulator is widely applied in the assessment of Navigational Safety in the har-

bour and waterway design. According to the needs of ENC(Electronic Nautical Chart) data in the navigational

assessment, this paper analyzes the source of ENC data, such as S-57 data, MVCF(Military Vector Chart

Format) data and CAD(Computer Aided Design) data. An effective method of ENC data generation has been

developed. Special techniques are investigated for generating ENC data, such as ENC data structure design-

ing, chart data conversion, digitization method of raster images of CAD design drawing, optimization ap-

proaches and data integration methods. Software has been developed to edit the chart data with good perfor-

mance. The technologies developed in this paper have been applied to more than 100 practical projects and

successful results have been obtained.

vessel with design tonnage under certain hydro-

logical and meteorological conditions. This step

is performed mainly through simulator opera-

tions, obtaining the width of the vessels’ paths

and the tracks of vessels out of control or drifting.

2 Assessing the capacity of berthing in the port.

The data to be assessed include the size and water

depth of manoeuvring area of the design quay.

Simulator checks are carried out to make sure the

requirements are met for safe berthing operations

of the vessel with design tonnage under certain

hydrology meteorological conditions. (Qian

2003)

In order to meet the needs of the navigational as-

sessment, the ship-handling simulator should pro-

vide the ENC data with large scales. Those data

should be organized with a rational structure. The

general precision of the ENC data is required to be

within the range of meter. And it is required that

ENC data must include the following details,

1 Lands and islands;

2 Quays, docks, bridges and inshore facilities;

3 Beaches, depths of water, depth contours and bot-

tom characteristics;

4 Channels, anchorage, security area and sea floor

pipelines;

5 Obstacles;

6 Aids to navigation;

7 For the ENC database used in the assessment, the

following demands should also be considered,

8 Good compatibility and expansibility,

9 Adapting of the standard electronic chart data

structure,

10 Adapting of the data of the design drawings of the

project,

11 Efficiency and costs,

12 Maintainability and portability.

Meanwhile, it must be easy to search and revise,

and in a hierarchical structure to raise the speed of

data processing.

3 ANALYSIS OF THE SOURCES OF ENC

DATA

The assessment of navigational safety in the harbour

and waterway design usually assesses the project

that is going to be implemented, or in progress of the

design phase. There is, therefore, no ready-made

nautical chart to be used. We can only combine the

design drawings of the project and the existing nau-

tical chart of water areas to set up specific ENC spe-

cific database to meet the needs. The sources of the

ENC data can include the existing paper nautical

chart, S-57 electronic nautical chart data, MVCF

electronic nautical chart data, CAD project design

drawings and satellite remote sensing image, etc. As

to the existing electronic nautical chart data, corre-

sponding format change is necessary, changing the

standard S-57 format data into the system defined

format data. Special processes are needed for other

sources such as paper nautical chart, satellite images

and CAD design drawings, etc.

3.1 S-57 data

The Standard IHO (International Hydrographic Or-

ganization) S-57 is the most popular ENC data

worldwide. It is designed to permit the exchange of

data describing the real world. The data produced is

organised into named structures. Usually, more than

one object is involved in an exchange. Therefore,

since an object is structured into a record, an ex-

change is comprised of more than one record. To fa-

cilitate this, records are grouped into files. The set of

information which is finally exchanged is called an

exchange set (IHO. 2000).

This standard defines a set of records from which

an exchange set can be built.

These records fall into five categories:

1 Data Set Descriptive Record：Containing infor-

mation about the coordinate system, the projec-

tion, the horizontal and vertical datum used, the

source scale and the units of height and depth

measurement, and information about the origins

of the data set.

2 Catalogue Record: Containing the information

required to allow the decoder to locate and refer-

ence files within the entire exchange set. This part

can be compared with a table of contents. It also

contains information about special relationships

between individual records within the exchange

set.

3 Data Dictionary Record: Containing the descrip-

tion of objects, attribute and attribute values used

in an exchange set.

4 Feature Record: Containing the non-locational re-

al-world data.

5 Spatial Record: Containing the locational data.

They may be of types of vector, raster or matrix.

An exchange set may contain a mixture of the dif-

ferent spatial record types. Among them, vector

records include the information about the coordi-

nate geometry related to the feature records, in-

cluding spatial attributes, topological relation-

ships and update instructions. Vector records may

be of types node, edge or area.

S-57 data can be obtained from the nautical chart

publishing department.

3.2 MVCF Data

MVCF is an abbreviation of the Military Vector

Chart Format, which is the digital nautical chart in-

terchange standard of China. It possesses the charac-

teristics of the following:

1 It is a kind of geographical datum model without

the topological relation, supporting the fast dis-

play and easy editing of the data;

2 It supports the index file. The structure of the data

is succinct;

3 It supports point, line, polygon and annotation

notes. Therefore it supports the exchange of the

whole nautical chart data elements;

4 Attribute is supported. The attribute of the vector

is stored in dBASE format file, and the attribute

record is the one-to-one correspondence with vec-

tor record.

MVCF data file is organized by the sheet of paper

chart. It adopts the catalogue structure. The cata-

logue name is the same as the serial number of digi-

tal nautical chart. MVCF data compose of four files:

basic file, shape file, index file and attribute file.

Among them, the shape file is a variable length rec-

ord file of direct access. It contains the coordinate

position data of the nautical chart. Index file con-

tains describe the offset of the beginning record cor-

responding shape file record. The attribute file is in

dBASE format structure. It contains the attribute of

the vector data. The shape file record is one-to-one

correspondence with the attribute file record.

MVCF data can be obtained from the Navigation

Support Department of the Navy Headquarters. The

nautical charts published cover the whole coast area

of China.

3.3 CAD engineering design drawing

Usually, software of AutoCAD is employed in mak-

ing the drawings of design projects of harbour and

waterway. These drawings include data of water ar-

eas and land-based areas, especially the newly-built

objects, such as quays, docks, bridges, channels and

navigation marks, etc. These designs are the target

of the safety assessment. The data may also include

harbour building, shipyard workshop and coastline,

etc., which are not as critical in safety assessment.

Hence, the data that we care about are only part of

the engineering drawings for the relating water are-

as, and it is unnecessary to change the whole CAD

file directly. By retrieving part of the data from the

drawings, information redundant can be avoided.

In China, the domestic coordinate system, BJ-

1954, is generally used in the design drawings. Ad-

ditional conversions should be made to ensure com-

patibility with the coordinate system, WGS-84, that

ECDIS adopts. In our research an approach is devel-

oped for the processing of the drawings. The CAD

data file is printed to a JPG image. Then, with digiti-

zation technology, vectorization operation of the

parts we need is performed. In order to improve the

processing efficiency, we only concern the newly-

built relevant objects, such as quays, docks,

manoeuvring areas, channels and navigation marks,

etc.

3.4 The satellite remote sensing image

The satellite remote sensing is the new technology to

obtain the information such as resource, environ-

ment and calamity in the coastal areas. It has some

conspicuous advantages, such as large-scale, high

efficiency, synchronization, high frequency of dy-

namic observation and so on. With the fast devel-

opment of the remote sensing and computer technol-

ogy, the satellite remote sensing can replace the

survey artificially with a great extent. It becomes a

important data source of the digital chart. It is a kind

of very economical and practical method to use the

satellite remote sensing image of high-resolution. By

digitization, Data of coastlines, quays, berths and

buildings can be obtained from satellite images.

4 THE STRUCTURE OF ENC DATA

To meet the requirement of the navigational assess-

ment, one structure of reasonable ENC data has been

developed and named as HYENC (Electronic Nauti-

cal Chart Local Defined). Conciseness and memory

saving are considered, and it is convenient for trans-

formation, renewal and maintenance, as well as fast

display.

HYENC data structure defines that each file rep-

resents one nautical chart. The file includes sheet da-

ta and figure data. The sheet data on the head of the

file contain 600 bytes for the control information of

each chart, and they are divided into 25 data items.

The figure data are variable length records of direct

access, recording the data of layers of each chart,

and per layer of data includes the head data of 108

bytes and the records of variable length. The record

counts and type are stored in the sheet data. The

structure of HYENC data is shown as Figure 1.

HYENC digital chart

Sheet datum

Figure datum

Layer datum

Record datum

Head (600b

)

(the control

information

of each chart,

it composes

of 25 data

items.)

Layer

Layer 2

……

Layer n

……

Head (108b)

Record 1

Record 2

……

Record n

……

Head

Data：

(Point、

Line、

Polygon、

Attribute)

Figure 1. The structure of HYENC data

The sheet data includes information such as the

name, range, scale, coordinate system of the nautical

chart. By this information, chart search can be per-

formed rapidly, and chart panning and seamless

splicing can be realized. The figure data is such

structured that it helps the hierarchical display of the

chart, as well as convenience for combining, adding

and deleting relative information.

5 THE METHOD OF ENC DATA GENERATION

5.1 ECDIS coordinate system and conversion

To display the chart on the computer screen, it needs

converting Mercator projection coordinate into com-

puter screen coordinate. When performing chart

work on ECDIS, we need to convert computer

screen coordinate into geographic coordinate. Con-

version and calculation of all kinds of coordinate in

real-time for the display and operation can influence

system performance of ECDIS.

For fast display, the ENC stores the point assem-

ble data in longitude and latitude coordinate. Longi-

tude data is in the unit of minute, and latitude in me-

ridional parts. When displaying the chart on the

computer screen, the time for converting latitude in-

to meridional parts can be saved, improving the

speed of displaying.

In ECDIS, the point of left bottom is taken as the

origin of coordinate with display format of north up.

We establish coordinate system that the OY axis is

upwards, OX axis rightwards. Suppose that a geo-

graphical coordinate point,

),(

000

λϕ

, corresponds to

screen coordinate point,

),(

000

xyP

, then any geograph-

ical coordinates and screen coordinates may be con-

verted using equation (1) and (2):

Longitude

converts into x:

fxx ×−+= )(

λλ

(1)

Latitude

converts into y:

fyy ×−−= )(

ϕϕ

(2)

where f is a scale, expressing the ratio of meridional

parts of geographical coordinate to the display

screen coordinate.

By the similar manner, it is easy to convert screen

coordinates into geographical coordinates.

When performing zoom in, zoom out, drag and

other operations, we can fast convert coordinates,

and display ENC figure on the computer screen.

Meanwhile, we use the screen clipping algorithm to

filter the ENC data. It filters out the data beyond

screen range, and improves the displaying speed of

ECDIS.

In the ECDIS, the geographical position is ex-

pressed in longitude and latitude coordinates, i.e.

degree, minute and second. Then the corresponding

algorithm of mutual conversion between latitude and

meridianal parts may refer the paper (Zhang 2003).

5.2 The procedure of ENC data conversion

For the assessment of navigational safety in the har-

bour and waterway design, the design department

supplies the project design drawing in CAD format.

We must use another method to obtain other data

such as the nearby coastline and channel. Through

the analysis described above, these data can be ob-

tained from sources such as paper chart, S-57 format

data, MVCF format data, remote sensing satellite

images and CAD project design drawings ,etc. These

data are mainly divided into two kinds, the digital

ENC data and raster image. For ENC data, we need

compile programs to apply converting of S-57 for-

mat data and MVCF format data, while a digitaliza-

tion is need for paper charts, remote sensing images

and CAD project design drawings. Then we inte-

grate all data into one ENC data file which serves

the simulation assessment. The converting proce-

dures are illustrated in Figure 2.

S-57data

MVCF data

Digitized

Combine all ENC data

Result ENC data for

Simulation

Check the size of the

design data in ECDIS

Format turn

Origin chart

CAD design data

Print to CAD map

Turn to DXF file

Print to base map

Intercept base

chart

Digitized

the part of CAD map

Accurate

Error happen

Paper Chart

Add to the base map

Turn water

sounding

Satellite

Picture

Figure 2. The procedure of data converting.

5.3 Digitization of raster images

Digitization is a very important step in the procedure

described above, i.e. use certain apparatus and soft-

ware to digitize raster image and convert them into

vector data. Hu (1999) recommended a method of

using digitizer to convert paper chart. This method

utilizes digitizer and corresponding software of col-

lecting ENC data together, which convert raster data

into vector data. The method which relies on cir-

cumscribed digitizer, a paper chart can only use on

one machine at a time. It is kinds of complicated in-

efficient to convert the data, and inconvenient to

modify latter data. The approach is kinds of ineffi-

cient and can hardly meet the requirement of project

research in the time limit.

A PC-based ENC data editor system is developed

to meet our needs. It uses the mouse and interface

software to digitize raster images. Firstly, it is im-

portant to determine the key point position i.e. its

longitude and latitude, the coordinates of the screen

of southwest and northeast point. We can obtain the

coordinates from the paper chart or the satellite re-

mote sensing image. After determining the key

point, we can display the raster image in PC-based

ENC data editor's system, and then use the mouse to

collect manually the point-line-face data of the chart.

The system automatically converts a mouse position

of the screen coordinate into geographical coordi-

nate, and save the coordinate data into the data file.

Figure 3. ENC data editor’s system.

We adopted layered storing and displaying tech-

nology of ENC data. We can digitally compile paper

chart on several PC at the same time, and collect all

the data into one file finally. Thus it can improve the

speed of making ENC data, and shorten develop-

ment period. Furthermore we may add, delete, edit

the data randomly and maintain the data convenient-

ly. Figure 3 illustrates the ENC data editor's system

software interface.

If the image is the CAD design drawing, we need

to convert the format of the CAD file into *.JPG im-

age. Then The ENC data editor's system software in-

terface is the image processing software such Pho-

toshop is used to superimpose the image with the

base map. The JPG format image needs to be

zoomed in or out in the same proportion. Firstly we

match the base map and the CAD design drawing.

Then the length of the quay or size of turning circle

area is measured by using the digitized system soft-

ware. The size is compared with the dimension of

CAD design drawing, and the difference proportion

is calculated. Secondly, adjust the size of JPG image

in the proportion until the two images are identical

in size. At last the composite image can serve as dig-

itized base map. When digitizing the image, we only

need to choose useful information, for example,

quay, dock, newly-increased coastline, turning area,

channel line, designed anchorage, navigation mark,

and depth of water and note information.

5.4 Generation of water depth data

Water depth is an important parameter in the as-

sessment of navigational safety in the harbour and

waterway design. The design water depth of chan-

nels or turning area should ensure enough Under

Keel Clearance (UKC) for vessels. The designer

supply CAD design drawings that includes survey

data of depth of water. We can obtain water depth

data according to the digitized method described in

Section 5.3. But it is relatively heavy workload to

input a large amount of depth of water manually. So

we plan to obtain water depth data with data conver-

sion method. Firstly export the CAD drawing format

file(*.DWG) as Drawing Interchange Format

file(*.DXF). Then extract water depth data from the

file with certain algorithm, and keep a series of

point, P (x, y, z), where the coordinate x and y ex-

press plane coordinate, and z express the depth of

water, into a collection. Finally convert the point

collection into ENC water depth data.

If there are no newly surveyed data, water depth

can be obtained from the present paper chart. We

can convert present S-57 format data or MVCF for-

mat data. Water depth data of S-57 format denote in

SG3D record, while water depth data of MVCF for-

mat are specially stored in the sounding layer. In the

ENC data editor’s system, we can use the mouse to

add, delete, and edit water depth data. Based on pre-

sent data of water depth, neural network technology

is used to carry out difference calculation (Shi

2004). While navigating in the simulation area, wa-

ter depth nearby the ship is detected in real-time, de-

termining whether the water depth of the channel

meets the demands or not.

5.5 Data combining and correction

In order to ensure the maintainability of ENC data,

we adopt layered processing technology, which clas-

sifies point object, line object and area object based

on different characteristic of ENC data. For example

water depth, navigation mark, marks on the bank are

inducted as point object; and coastline, depth con-

tour and submarine cable, etc are inducted as line

object; land, island and quay, etc. are inducted as ar-

ea object. Because of data the layered structure, we

can integrate pieces of ENC data easily. There are

two kinds of situations. One adds data of additional

map directly to base map data, at the same time ad-

just the sheet data of base map, thus additional map

will overlay on the base map. Second method is to

integrate the index number of layer data of addition-

al map and layer data of base map corresponding to

the index of layers.

In order to maintain ENC data and develop ENC

editor system, when we edit point, line and area ob-

ject, only the mouse is needed to finish adding, cor-

recting, deleting of the point collection, and to edit

attributes. Several computers can work simultane-

ously on one chat, and the generated data are put to-

gether finally, improving the efficiency of making

ENC data.

6 CONCLUSIONS

Navigational simulator is widely applied to assess-

ment of navigation safety in harbour and waterway

design at present, but the ENC data are the funda-

mental element of the simulation. The ENC data

produced by above described method can be applied

to two-dimension ship handling simulation system.

Meanwhile, it is the source of the simulation radar

echo data and coastline, port building and topogra-

phy of three-dimension visual system in large ship

simulators. In this way, we can make all data totally

identical, ensuring reliability of the simulation re-

sult. Software has been developed to edit the chart

data with good performance. The technologies de-

veloped in this paper have been applied to more than

100 practical projects and successful results have

been obtained.

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