Integration
The integration process began by looking at the
implementation requirements, drawn from both the SRD and SAD along
with discussions with the algorithm development team. Specifically
consideration was given to three main areas:
- Support of the all algorithmic modules operation
- Support of algorithmic testing
- Support integration and system test
To support the operation of the algorithmic modules,
i.e. system I/O, image analysis, threat detection and man machine
interaction, a dataflow architecture was selected. Portioning of
the SUBITO data flow was carried out according to the functional
needs with the resulting implementation schema shown in the figure
below.
Implementation Architecture
The I/O services and collaboration schema was
implemented to allow the system to obtain images directly from
on-line cameras, video recorded sequences or as a collection of
image files. Applications were constructed to a common paradigm
which allowed development of the algorithm modules to occur in
different environments (Linux and MS Windows) depending on the
developers' preference.
The data exchange uses a common database, which
guarantees platform independence but pays a price in system
performance, although this did not prove to be a constraint in
the SUBITO implementation. Only processing results were exchanged
via the system database, the video imagery was accessed using a
custom API created for that specific purpose.
In general applications implement a simple loop
including:
- • Read image,
- • Process image frame(s),
- • Send eXtensible Markup Language (XML) data to the database.
Those applications not requiring images simply
loop on the database, reading, processing and writing data therein.
To support the algorithm testing it was decided
while defining the implementation requirements that it would be
beneficial to utilise the same I/O API at the developers' site
to support individual algorithm module testing as was to be used
in the final implemented system. Thus the developers' could be
confident that the developed modules could correctly access the
image streams when integrated with the other component modules.
For support of system integration and test a
communication framework was defined which provided a flexible
mechanism to switch between online and offline operating modes.
This combined approach would be used to verify the system performance
allowing recorded test video sequences to be submitted to the
system and the resulting output data collected. The same data
could also be played back offline, with the MMI allowing the
operator to examine in detail the system behaviour and outputs.
With the implementation requirements defined,
the focus of the work then moved to the actual hardware integration.
The approach adopted was to separate the logical components forming
the physical architecture and provide loose coupling of the modules.
The primary requirement was for an efficient yet
flexible system, with respect to:
- Multiple and heterogeneous platform support;
- Use of field devices;
- Simplicity and uniformity of the interface;
- Simplicity of the data exchange mechanism.
The platform support was provided by a collaborative
model, which with the exception of image data took the form of
XML data, exchanged via database tables in a Structured
Query Language (SQL) database. Information in the database is
synchronised via time tags applied to the data as it is written
to the database, which allows the system modules to consume data
either one entry (image) at a time or in batches, without the need
to know a priori the granularity of the data.
The flexibility in the use of test equipment was
motivated by the need to be able to incorporate easily changeable
configurations, e.g. camera Field of View, orientation etc., however
the camera type was limited to analogue cameras as this corresponds
to the reality of current surveillance installations and provides
an immediate measure of SUBITO with the surveillance market.
The cameras used on the test site were PTZ, but
were optimised for orientation and focal length until the most
suitable arrangement was found to meet the demonstration requirements,
from which point on they were used as fixed cameras. Encoders
connected to the cameras translated the analogue signals to digital
data for use in the rest of the system.
Consideration of the applicability of the SUBITO
results to real life situations, e.g. public buildings and spaces,
suggested that the test site be of medium to large size, and in
practice the area eventually chosen was approximately 40 by 40
metres and can be considered similar to many public buildings.
With the implementation architecture and test site
defined, the task of off-line data collection commenced to provide
representative test data to the algorithm developers and to provide
data for use in the test and validation of the SUBITO results.
The scenarios used for the data collection were chosen to satisfy
the following requirements:
- Provide a set of videos covering all the expected project
objectives
- Provide a set of videos containing scenarios that are complete,
self explanatory and measurable
- Perform the recordings according to the standing laws and
rules for privacy: personal image rights, privacy of the public,
compliance with surveillance cameras laws.
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