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REMOTE UPDATING OF RASTER IMAGES OF NAUTICAL NAVIGATION
CHARTS OVER THE INTERNET1
Yu.G.Vasin2, S.V.Zherzdev2, E.S.Sorokin2
2
State Research Institution - Research Institute for Applied Mathematics and Cybernetics,
NNSU, 603005, Russia, Nizhni Novgorod, Ulyanov street, 10,
tel.: (831) 236-23-61, e-mail: [email protected]
The technology of organization of remote updating of raster images of nautical
navigation charts (NNCs) on ships with the use of global data transmission networks is
proposed. The proposed and implemented methods allow the actualization of NNCs to
be made in an automatic mode with minimal requirements to channel capacity.
It is unthinkable to ensure the safety of
navigation without updated (actualized)
versions of naval navigation charts (NNCs) on
board the vessels. At present, the updating of
paper NNCs on the vessels via communication
channels is carried out as follows. Notices are
transmitted to the vessels in the PDF format
with the description of changes that should be
plotted.
The notices are presented to mariners in the
form of text instructions or graphic fragments
of NNCs (inserts). The vessel’s navigator,
having received the notice, manually makes
respective changes on the paper NNCs. The
main disadvantages of such approach are a
relatively large volume of the data transmitted
(especially graphic inserts), great volume of
manual work for the actualization of paper
NNCs and, as a consequence, the human factor
(mistakes made by the navigator).
With the development of the means for
automation of navigation and for solving
navigation problems and the problems of
navigation safety, more and more often raster
and vector NNCs (for example, in the
international format S-57) are used on the
vessels alongside with paper charts. However,
the problems connected with the updating of
all kinds of charts still remain.
In the Research Institute of Applied
Mathematics and Cybernetics, an essentially
new technology of remote editing (updating)
of raster images of NNCs has been developed
that involves the actualization of raster NNCs
at the center on the shore using the Notices to
Mariners. The results of this updating are used
for editing the collections of raster NNCs on
board the ship over the Internet in a
completely automatic mode without any
human participation. Thus, the volume of
information transmitted via communication
channels for updating is negligibly small in
comparison with the original data (less
than 1%).
Further, the stage of development of this
information technology is considered. This
stage is directly related to synchronization
(matching) of raster images of NNCs.
The proposed technology is based on the
development and adaptation of the following
mathematical models and methods:
- Mathematical models, methods and
technologies
of
hierarchical
adaptive
compression of graphic information;
- Hierarchical representations of information;
- Methods for construction of hierarchical
spatial digests;
- Effective algorithms for comparison of
hierarchical spatial digests;
- Remote access to large-format raster
images with level-by-level data transmission.
For solving the problem of synchronization of
images with the minimum requirements to the
capacity of communication channels, a two-
_______________________________________________________________________
The work was performed with the support of RFBR (Project №05-01-00590).
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stage algorithm for information exchange has
been proposed.
At the first stage, differing fragments of the
images are identified at the server (the new
version) and at the client (the old version) and
the information on the changes is transmitted.
The principal idea is to use digital hierarchical
digests for the comparison of fragments
without transmitting the raster data of these
fragments. The identification of image blocks
requiring a repeated loading is based on the
fact that the changes that have been
introduced, as a rule, are localized in space.
The algorithm effects a hierarchical division of
the sheet of the chart into decreasing blocks
for checking their identity, starting with the
check for any changes of the whole sheet and
finishing by revealing the concrete changed
fragments. At each step the server and the
client calculate and compare the values of the
digests of the corresponding portions. The
algorithm is applied recursively to those
portions whose digest values differ at the
server and at the client. This procedure allows
to reveal the fragments that require updating
with minimum expenditure of time.
At the second stage, the problem of
construction of the updated image is solved.
For the realization of the second stage, the
block structure of the file in a hierarchical
format is essentially used, which permits to
manipulate rather small fragments of the
image independently.
The following stage in the development of the
technology for updating raster images of
NNCs is the creation of a full-fledged system
for controlling the versions, taking into
account the specific nature of geodetails,
unlike the commonly used general purpose
version control systems that are designed, first
of all, for effective work with text (linearlyordered) data. The proposed system provides
for the storage of the whole chain of NNC
versions with minimum use of disk resources.
To achieve this, as a new version of the image
file of NNC is entered into the system, the
search of the changed image fragments is
effected and they are stored in a compact
difference file. The structure of the versions
storage ensures rapid retrieval of any version
of the NNC, storage of any auxiliary data for
each NNC version, and remote updating of any
version of electronic NNCs to the actual
condition with minimum volume of data
transmitted over the network. The use of
unambiguous version labels allows to exclude
the stage of determination of the current state
of the NNC on the client’s side from the data
exchange in the network. Besides, it is
possible to construct and transmit effectively a
"cumulative" updating package. It means that
all the corrections between the user’s inquiries
about updating are merged, and all the
duplicated data are excluded, so that only the
last versions of the repeatedly changed
fragments are transmitted.
The described technologies are realized in the
form of separate applications or program
modules. Compatibility with the existing
system of electronic charts archive is provided.
It is possible to receive and print out the
inserts for paper charts using the updating
protocols of raster NNCs.
Experimental testing has confirmed the
efficiency of the proposed technology, when
raster NNCs were updated using Notices to
Mariners. The volume of the information
transmitted to the ships over communication
channels did not exceed 1% of the original
data volume.
References
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methods for the processing of graphic information. //
Automation of processing of the complex graphic
information: Inter-university collection of papers.
Gorky State University, Gorky, 1984, p.131. (in
Russian)
2. Vasin Yu.G. Efficiency of various strategies of
video information processing on the basis of local
homogeneous recurrently-recursive functions //
Methods and means of processing of the graphic
information: Inter-university collection of papers.
Gorky State University, Gorky, 1986, pp.4-47. (in
Russian)
3. Vasin Yu.G., Zherzdev S.V. Technology of
hierarchical coding of video information // Abstracts
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graphics and machine vision GraphiCon'2002.
N.Novgorod: NGASU Publishing house, 2002,
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Hierarchical access to large-format images in the
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Internet // Abstracts of VIII All-Russia scientific
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