Cryptography Reference
In-Depth Information
6.1.1 The Necessities of GIS Data Watermarking
Generally, GIS data is of great value. The acquisition of vector maps is a high
cost process, in which the high precision instruments and a large amount of
physical and labour resources are required. The digitization and the vectoriza-
tion of original data also represent hard work to produce the required vector
maps. Consequently, digital maps in GIS normally cannot be used without
cost. The application of GIS has to share its geographical data within the
user group in many ways. For example by the via web, or by CD. It means
that the map owner must provide some map copies to the users and con-
sumers. This makes the protection of the distributed data sets a crucial issue.
There are some special environments, where extra security requirements are
needed, especially for sensitive usage. For instance, the application of secret
military digital maps requires the capability of authenticating the source of
map data as well as confirming the integrity. Digital vector maps are still
unable to take the place of traditional paper maps until these requirements
can be met. Watermarking can provide solutions to the above issues. A map
owner can embed the product ID into the vector maps before distribution in
order to protect the copyright. The sources of military maps can be traced
by hiding unique identifications in them. Data hiding can also be a feasible
method of integrity verification or secret communication by using the hash
value or the secret message for the hidden data. Compared with general mul-
timedia data types, there are relatively few research works done in the area
of vector map watermarking. To our knowledge, a corporation in Uruguay
named
The Digital Map Ltd
is going to patent a copyright protection scheme
for vector maps where a watermarking scheme for polygonal data is utilized.
A commercial software called
MapSN
has also been developed for digital map
producers [1].
6.1.2 Characteristics of 2D Vector Map Data Hiding
The data structure and the application of 2D vector maps are also distin-
guished from the pixel images as well as other multimedia data types. This
results in the differences between the vector map watermarking and the gen-
eral multimedia watermarking in many aspects. For example these concern the
basic principle for data embedding, and the criteria for fidelity evaluating. All
above features should be considered when hiding data in vector maps.
Vector Maps: Data Structure and Basic Embedding Principle
Generally, a vector map is formed by Spatial Data, Attribution Data, and some
additional data used as indices or extra descriptions. Spatial data normally
takes the form of a sequence of 2D coordinates which describe the geograph-
ical locations of the map objects which represent the geographical objects in
the real world. All map objects can be categorized into three basic geometrical
