International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 1
Number 4
December 2007
395
Specificity of ENC Data Representation on an
Archipelagic Sea Area – Example of the East
Coast of the Middle Adriatic Sea Area
T. Duplancic Leder
Hydrographic Institute of Republic of Croatia, Split, Croatia
ABSTRACT: Production of ENCs is based on the theory of multiscale data management (usage bands) and
multiple representation of ENC data, controlled by scale minimum (SCAMIN) attributes. This paper presents
a solution to the problem of multiscale data management and multiple representation as a part of ENC data
production for archipelagic sea areas, using the east coast of the Middle Adriatic Sea area as a typical
example. This study is based on a long-standing experience in the production of paper charts and recently
ENC production for eastern coast of the Adriatic Sea, which is believed to be the second largest archipelagic
area in the Mediterranean. A new method of using SCAMIN attributes for archipelagic seas was proposed,
based on Canadian method. Also, a new usage band scale range, compilation scale (twice the chart scale) for
all navigational purposes and method of using SCAMIN attributes for archipelagic seas are proposed.
1 INTRODUCTION
The Hydrographic Institute of the Republic of
Croatia (HIRC) issues about 100 navigational charts
and 30 nautical publications. Production of
electronic nautical charts (ENC), according to
International Hydrographic Organization (IHO)
specifications S-57 Edition 3.1, started in HIRC in
2001. Croatia started ENC production within the
North Adriatic VRENC international pilot project, in
cooperation with the Italian company C-Map
(Altamura, 2003). HIRC and C-map adopted the
paper chart compilation scale, which proved to be
inadequate for an archipelagic sea (Duplančić Leder
and Lapaine, 2005).
The Croatian part of the east coast of the Middle
Adriatic Sea area is archipelago area (which is
believed to be the second largest archipelagic area in
the Mediterranean), filled with islands and shallow
waters. In an archipelago area navigation is
demanding and complex. Besides, the proposal of
chart classification according to navigational
purposes does not meet specific qualities of the
Croatian part of Eastern Adriatic coast (archipelago
area), and it is not consistent with the HIRC tradition
of paper chart production.
In 2006 HIRC started its own production of ENC
data. During the ENC production of an archipelagic
area, the high object density on the computer screen
was apparent. It was concluded that an ENC
produced with the paper chart compilation scale
contained too many objects that then caused clutter
on an ENC. In order to reduce the clutter or density
of objects on the display, a new usage band scale
range for the Croatian part of the Adriatic Sea and
ENC compilation scale for all navigational purposes
has been proposed. Moreover, a new method of real-
time generalization of ENC content by using method
of SCAMIN attribute coding was proposed.
396
2 ENC CHARACTERISTICS
2.1 ENC usage band and navigational purposes
The same area and ENC cell objects could be used
on different representation levels in different themes
or navigational usage, called multiscale data
management model. Such model imposes that the
data be passed to users on board grouped into usage
bands according to navigational purposes, which
mariners use depending on the situation. For
example, when a ship approaches harbour from the
open sea, navigational purposes change from an
overview one (minimum details), through general,
coastal, approach, and harbour navigational purposes
to anchorage navigational purpose (most details).
S-57 standard (IHO, 2000) requires that each
ENC cell be marked into 6 categories or usage bands
(Table 1) according to navigational purpose, depend-
ing on the scale of the source material. Each ENC
producer shall be responsible for assigning a
navigational purpose to a particular cell. By assig-
ning usage bands to ENC cells, their users will get
information for which navigational purpose the ENC
was produced (IHO, 2002 and 2003).
S-57 standard does not prescribe the scale ranges
assigned to particular usage bands or the minimum
or maximum scale for each usage band. The standard
allows chart compilers to adapt the scale range
within a navigational purpose to their needs. It is
recommended that the selection of ENC compilation
scale be based on the standard radar sequence
(Urlich et al., 1997; Table 1).
Table 1. Interdependence of usage band, navigational purpose,
scale range, compilation scale and radar range (according to
IHO, 2004a and b; Urlich et al., 1997)
Navigation
al
purposes
Usag
e
band
Scale
Range
1:
Available
compilation
scales 1:
Radar
ranges
(NM)
Overview
1
<1 499
999
1 500 000 –
3 000 000
and smaller
96 –
200
General
2
350 000 –
1 499 999
350 000 –
700 000
24 – 48
Coastal
3
90 000 –
349 000
90 000 –
180 000
6 – 12
Approach
4
22 000 –
89 999
22 000 –
45 000
1,5 – 3
Harbour
5
4 000 –
21 999
4 000 –
8 000 –
12 000
0,25 –
0,5 –
0,75
Berthing
6
> 4 000
3 999
and larger
< 0,25
Most of ECDIS systems allow their users to select
the display of ENCs according to usage bands, but
not according to navigational purposes, which
requires that the relation between the scale group
and navigational purpose of the chart be defined
(Table 1). By designing the process of ENC
production, to each usage band a particular scale
range is assigned. For example, an approach ENC of
usage band 4 will appear on the ECDIS screen at
1:22 000 to 1:45 000 scale, which corresponds to a
radar range of 1.5 to 3 NM. Position coordinates in a
cell are calculated from the centre (according to
established standard the ship position is plotted in
the centre of the screen display) (Greenslade, 2003).
Figure 1 shows the concept of ENC reading into
memory by selecting ENC from the chart list. When
a ship approaches harbour from the open sea, ENCs
of different usage bands and navigational scales
from A through B, C, D and F to G change on
ECDIS (Hecht and all., 2002).
Fig. 1. Selection of chart from the preliminary chart list
(according to Hecht et al., 2000)
2.2 Proposal of usage band range for the Croatian
part of the Adriatic
According to Recommendation for Consistent ENC
Data Encoding (IHO, 2002, 2004a and b) adopted at
the meeting of CHRIS Working Group, it has been
proposed that the compilation scale should be
assigned to each navigational purpose (Table 1). It is
a modified proposal based upon two IC-ENC
documents (IHO, 2004b), adopted at the meeting of
TSMAD Working Group. These documents are
intended to give recommendation and guidance to
Hydrographic Offices in the production of ENCs.
However, it should be pointed out that they leave
them a possibility of assigning their own scale
ranges to particular areas by means of specified
navigational purposes.
Studying of different proposals and
recommendations for the classification of scale
ranges for each of the six navigational purposes
proposed by CHRIS and TSMAD Working Groups
(Table 1; IHO, 2004a and b) has led to a conclusion
that none of the proposed classifications is adequate
for the Croatian part of the Adriatic. Taking into
consideration the proposed recommendations, a new
classification of scale ranges for navigational
purposes is proposed to be adopted at the HIRC. In
Table 2 it is proposed to assign navigational
purposes to a number of scales, with respect to
archipelagic characteristics of the Croatian part of
the Adriatic Sea and cartographic tradition of the
HIRC.
397
Table 2. Assigning of navigational purposes to a number of
scales (according to Duplančić Leder and Lapaine, 2005)
purposes
Usage
band
Scale
Range
1:
Available
compilation
scales 1:
Selectable
radar
ranges
(NM)
1
400 000
and
smaller
400 000
and smaller
48 - 96 -
200
2
90 000 –
399 999
180 000 -
350 000
12 - 24
3
45 000 –
89 999
45 000 –
90 000
3 - 6
4
22 000 –
44 999
22 000
1,5
5
4 000 –
21 999
4 000 –
8 000 –
12 000
0,25 - 0,5
- 0,75
6
4 000
and larger
3 999
and larger
< 0,25
2.3 Proposal of the compilation scale for the
Croatian part of the Adriatic
Compilation scale is the scale at which the data was
originally compiled, for example, it may define the
scale of the paper chart from which the data was
digitized (IHO, 2000). It turned out that using the
paper chart scale as compilation scale often resulted
in a cluttered screen display (Duplančić Leder and
Lapaine, 2005), especially in archipelagic areas with
numerous islands and islets. Being difficult for
navigation, such areas are heavily marked with
navigation signals (lights, beacons and buoys). On
the basis of the scientific research carried out by the
HHI it was proposed that the ENC compilation scale
for the Croatian part of the Adriatic should be twice
as large as the paper chart scale (Fig. 2).
Fig. 2. Example of ENC of Šibenski Cannel with a compilation
scale equal to that of the paper chart (left) and compilation
scale twice the paper chart scale (right)
3 USING SCAMIN
3.1 Using SCAMIN attributes for multiscale data
management on the east coast of the Adriatic
Sea
According to S-57 standards, the ENC database was
build as a multiscale database which stores nautical
data at different scale levels (several digital dataset -
ENC cells). This makes it possible for the data be
provided to the ship as a set of “navigational usage”,
allowing the navigator to adapt appropriate usage to
the situation. According S-57 standard, ENC is
assigned to one of the 6 usage bands dependent on
its intended navigational purpose (IHO, 2004b). As a
vessel moves from the open sea towards port, the
navigational usage shifts from an overview (least
detailed), through general, coastal, approach and
harbour level to berthing level (most detailed).
When zooming out the compilation scale (the
scale on which the data was originally compiled -
attribute “Compilation Scale of Data” CSCALE;
IHO, 2000) or using ENC cell for other navigational
purposes, an ECDIS display becomes crowded.
Therefore, to reduce clutter on an ECDIS display it
is necessary to use SCAMIN (scale minimum)
attributes. SCAMIN is the S-57 attribute designed to
provide the means for controlling on-line generaliza-
tion and multiscale ENC data management in the
ECDIS (Vachon, 2003). SCAMIN attribute
represents the minimum scale at which the object
may be used (e.g., for an ECDIS presentation). IN
order to optimize the performance and clarity of the
ENC data, it is strongly recommended that SCAMIN
is used (IHO, 2000). SCAMIN attribute allows
optimal nautical data representation for any scale
and purpose.
The experiences of other countries in using
SCAMIN attributes, reported by Bisset and Fowle
(IHO, 2003), indicate that most of the hydrographic
offices use one of two methods: the semi-automatic
method proposed by an expert group from the
Canadian Hydrographic Service (Vachon, 2003), and
an automatic method suggested and initiated by the
expert group of 7Cs, a German producer of the
software package for ENC cell creation (Ulrich et
al., 2003). The German (7Cs) and Canadian (CHS)
methods of assigning SCAMIN attribute values are
based on their own experiences. In analysing these
methods we determined that neither of them was
entirely suitable for archipelagic sea areas (e.g.,
eastern Adriatic, Croatia, Greece, Sweden, Norway,
Finland, etc.). Therefore we propose a new method
of using SCAMIN attributes for archipelagic seas.
Among available methods, we took the Canadian
method of on-line generalization and then modified
and adjusted it further for an archipelagic sea such as
the Middle Adriatic.
A new method (named the Croatian method) of
cartographic rules for applying SCAMIN objects
coding based on the tradition of compiling charts at
the HIRC (Duplančić Leder and Lapaine, 2005),
classified all ENC objects into 4 groups according to
their navigational purpose and each group includes
objects that should be used for the particular
398
navigational purpose (Duplančić Leder et all, 2007).
The objects on harbour and berthing charts belong to
the same group.
SCAMIN value for the particular group was
calculated by the formula:
( )
9,0*__ factorSCAMINCSCALEvalueSCAMIN ∗=
(1)
CSCALE is compilation scale of ENC cell.
This formula was obtained by experimental
examination of percentage decrement of SCAMIN
value, ranged from 5% to 25%, by comparison and
result analogy with the Canadian method. It was
found that the SCAMIN value decreased by 10%
gives the optimal density display for an archipelagic
sea area (Duplančić Leder, 2006). So, formula (1) is
a modification of the Canadian formula, in such a
way that SCAMIN value is decreased by 10%. The
SCAMIN values resulting from formula (1) are in
agreement with the Croatian method of navigational
purposes assignment to scale range and compilation
scale proposal for Croatian part of the Eastern
Adriatic Sea (Table 2).
The method of real-time ENC content
generalization was presented in Duplančić Leder et
all (2007; Fig 3).
Fig. 3. Wider area of Telašćica Bay (scale 1:90 000) without
SCAMIN (left) and with SCAMIN (right)
4 CONCLUSION
During ENC production of the Croatian part of the
east coast of the Adriatic Sea area, which is a very
complex navigational area, considered as an
archipelagic sea, object density on the computer
screen was apparent. In order to reduce the clutter or
density of objects on the display, especially when
zooming out, a new usage band scale range for
archipelago sea area and compilation scale (twice the
chart scale) for all navigational purposes has been
proposed, according to IHO guidelines and IC-ENC
recommendation for “Improving ENC Consistency”.
In addition, a new method of multiscale ENC data
management by using method of SCAMIN attribute
coding was proposed. This method, as opposed to
previously known methods, used a new formula for
calculating SCAMIN attribute value and proposed a
new classification of Geo object groups, in
compliance with specific features of the Adriatic
Sea. This method was developed by modification of
the Canadian method. Since this method brought
some original solutions we named it the “Croatian
method of multiscale ENC data management”. The
method is in compliance with the traditional
production of charts at the Hydrographic Institute of
the Republic of Croatia and was demonstrated on a
coastal ENC of Šibenik Cannel and Telašćica Bay.
With slight modifications, this method could be
applied to other archipelagic sea areas.
REFERENCE
Altamura F., 2003. Mediterranean North Adriatic Pilot Project,
2nd International ECDIS Conference “ECDIS for Coastal
and Ocean Navigation”, http://www.ecdisnow.org/ (1. 6.
2005.)
Duplančić Leder, T. 2006. A New Approach to Electronic
Navigational Charts Production in Croatia, Doctor Thesis,
Geodetic Faculty of Zagreb University, 136. (in Croatian)
Duplančić Leder, T., Lapaine, M. 2005. Assigning S-57
SCAMIN attributes for archipelagic seas: Eastern Adriatic
Coast Experience, The International Hydrographic Review,
Vol., 6 No. 1, 33-43.
Duplančić Leder, T., Lapaine, M. 2007. Multiscale ENC Data
Management on Eastern Coast of the Adriatic Sea as an
Archipelagic Sea Area, Journal of Navigation, Vol., 60 No.
2, in press.
Greenslade, B. 2003. UKHO Generic ECDIS Kernel,
TSMADWG meeting, www.iho.shom.fr (1. 6. 2005.)
Hecht, H., Berking, B., Büttgenbach, G., Jonas, M., Alexander,
L. 2002. The Electronic Chart: Functions, Potential and
Limitations of a New Marine Navigation System, GITC bv,
Lemmer, Netherlands, 283.
IHO 1994. Hydrographic Dictionary, IHO Special Publication
No. 32, Edition 5, International Hydrographic Bureau,
Monaco, 280.
IHO 1997. Glossary of ECDIS - Related Terms, III Edition,
International Hydrographic Organization, Monaco, 24.
IHO (2000). IHO Transfer Standard for Digital Hydrographic
Data. 3.1 Edition, IHB, Monaco.
IHO 2002. Minutes of 9
th
TSMADWG meeting, October 2002,
IHB, Monaco, www.iho.shom.fr (1. 6. 2005.)
IHO 2003. Minutes of 10
th
TSMADWG meeting, October
2003, International Hydrographic Bureau, Monaco,
www.iho.shom.fr (1. 6. 2005.)
IHO 2004a. Recommendation for Consistent ENC Data
Encoding, www.iho. shom.fr/COMMITTEES/CHRIS (1. 6.
2005.)
IHO 2004b: Improving IC-ENC Consistency, CL 47/2004,
www.iho.shom.fr (1. 6. 2005.)
IHO 2004c. Electronic Navigational Chart (ENCs) “Production
Cookbook” – A guide to the requirments and processing
necessary to the produce ENCs, IHB File No.
S3/8152/WEND.
Vachon, D. (2003). Canadian Implementation of SCAMIN
Attribute for ENC. online at http://www.openecdis.org/
Ulrich C., Rottmann, E., Büttgenbach, G.B. (2003). SCAMIN -
The Tool to control Online Generalization,
http://www.openecdis.org/ discussion/scamin /scamin.Html