One of the current directions in the
development of unmanned aerial systems is the application of unmanned aviation
in the field of cargo transportation [1, 2]. Specialized transport unmanned
aerial vehicles (UAVs) can be effectively utilized for the delivery of
essential goods to remote areas with limited or seasonal ground access,
including regions affected by natural disasters. As noted in [1], the use of
UAVs in such cases contributes to a reduction in flight-hour costs, decreases
dependency on weather conditions, and eliminates risks to human crew members in
emergency situations during mission execution. Other relevant and in-demand
applications of UAVs in the cargo transportation domain include the transport
of hazardous or condition-sensitive goods; delivery of seeds, fertilizers, and
samples of soil or plants between remote field stations and laboratories; and
the movement of cargo between warehouses and distribution centres, among
others.
In light of the above, a pressing challenge
is the development of robotic unmanned aerial transport systems (UATS) for
cargo transportation applications. A key component in addressing this challenge
lies in the development of mathematical models, information systems, and
software tools for UATS control systems [3], including data storage,
processing, and analysis platforms; automated control systems; communication
subsystems; information-analytical platforms; and decision support systems.
Decision-making support is required both during the execution of flight missions
and at the planning stage.
Planning flight missions for UAV groups
engaged in cargo transport involves a set of interrelated tasks, such as the
formulation of cargo transportation plans, the selection of UAVs with specific
operational characteristics, and the development of UAV loading plans that
account for the properties of the transported cargo and a range of
transportation-related constraints [4]. Each of these tasks demands the
consideration and analysis of extensive, multidimensional data sets that may
differ in format, structure, and source.
For example, when developing cargo transportation
plans optimized according to specified performance metrics, it is necessary to
account for various parameters, including the condition of the route network,
cargo characteristics, their distribution across source locations, and the
current status of delivery orders with respect to their priority levels. In
turn, information about the route network must include data on the throughput
capacity of individual routes and the resource costs associated with employing
particular UAV types. These costs may include, for instance, total route
traversal time (including time for preparatory and ancillary operations), the
cost of transporting various types of cargo, and other relevant operational
metrics.
These features give rise to novel
formulations of cargo transportation plan optimization problems, which require
the simultaneous consideration of multiple types of constraints and conditions.
Several such problem statements are examined in [5, 6], where corresponding
optimization models are developed and algorithms for determining optimal
cargo transportation plans are proposed. At
the same time, an essential aspect of implementing comprehensive software
support for these models and algorithms is the development of visual interfaces
that enable interactive specification of model parameters and facilitate the
presentation of optimization results. This, in turn, necessitates the
application of appropriate techniques and methods for the visualization of
multidimensional data.
The problem of constructing visual models
for cargo transportation optimization has been addressed in a number of
studies, including [7, 8]. However, these works primarily focus either on the
visualization of the graph structure of the transport network—without
incorporating many of the aforementioned parameters that characterize the
optimization model as a whole – or on simulation-based modelling of
pre-constructed cargo transportation plans. In this paper, we propose an
approach to the development of visual models intended to support the
interactive specification of parameters for the cargo transportation planning
problem, as well as the visualization of optimization results through a
graphical user interface, including within geographic information system (GIS)
environments. The proposed approach is grounded in the concepts of
visualization metaphors [9] and the cognitive clarity of visual representations
derived from them [10]. We illustrate this approach using the example of
constructing a cargo transportation plan for heterogeneous cargoes delivered by
UAVs under constraints imposed by limited route network capacity and considering
the prioritization of delivery tasks [5].
We address the problem of constructing an
optimal cargo transportation plan between source nodes (hubs) and destination
nodes (points of demand), considering the presence of intermediate nodes within
the transport network, where both UAV maintenance and cargo redistribution
operations may be performed. The objective is to determine which of the
currently available routes—accounting for the state of the transport network – should
be utilized for cargo delivery, as well as to specify the quantity of each
cargo type to be transported along the selected routes in order to fulfil
existing delivery requests. The model accounts not only for potential shortages
of certain cargo types, but also for scenarios in which it is not possible to
fully satisfy demand due to the limited throughput capacity of the available
routes.
Let
be a directed graph representing the current state of the transport network, where A is the set of nodes corresponding to the network’s vertices, and W is the set of arcs representing the connections between these nodes. The absence of an arc (i, j) in W indicates that, in the current state of the transport network, a direct UAV flight from node i to node j is not feasible.
For each node
,
we define two subsets associated with this node from the set A:
∙
,
ected to
node i by an incoming arc;
∙
,
which contains the nodes to which node i is connected by an outgoing arc.
Let G = {G1, G2, …, Gp} denote the set of cargo types, and let
be the set of node capacity values for each
cargo type Gk. The interpretation of
is as follows:
∙
If
,
then node
i
is a source of cargo Gk, with
representing the available stock;
∙
If
,
then node i is a sink (consumer) for cargo Gk, and
represents the demand volume;
∙
If
,
then node i is a transit node for cargo Gk.
– denotes the cost of transporting a unit of cargo Gk
along the route (i, j). It is assumed that
.
If the transportation of cargo Gk
along route (i, j) is prohibited for a given k, then the cost is set to
.
In practical implementations, this can be represented by a sufficiently large finite value,
for instance, one or two orders of magnitude greater than the maximum cost
value in the set C). Such routes are referred to as
forbidden for the k-th cargo type.
represents the quantity of cargo units Gk, transported along the arc
(i, j); thus, the set X defines the cargo transportation plan.
denotes the capacity constraints of the
routes. If the capacity of route (i, j) is
unbounded, it is formally assumed that
.
One may consider the subset
,
consisting exclusively of those arcs subject to capacity
limitations, i.e.:
.
When it is infeasible to transport the
entire volume of cargo due to these capacity restrictions and potential
shortages of certain cargo types, the cargo transportation plan must be
constructed to prioritize the fulfilment of the highest-priority demands, with
the objective of maximizing the total cargo flow through the network.
Let us define the cargo flow Gk as
the total volume (number of units) of the given cargo delivered to the nodes
that serve as its sinks, i.e., nodes for which (
):
.
The total flow is then defined as the
aggregate volume of all cargo types delivered to all sink nodes.
Thus, the problem can be viewed as a
generalization of the classical maximum flow problem [11], extended to account
for cargo heterogeneity and an arbitrary topology of the routing network:
|
(1)
|
subject to the
constraints
|
(2)
|
Under the given conditions, where constructing a complete cargo transportation plan is infeasible,
the following types of problems related to the prioritization of cargo delivery may arise [5]:
1. It is necessary to ensure the delivery of each
cargo type to its most prioritized sinks. This problem will be referred to as
the “sink priority for cargo” scheme.
2. It is necessary to supply each sink with the
cargo types that are most prioritized for it. This problem will be referred to
as the “cargo priority for sink” scheme.
3. The needs of the highest priority sinks must be
satisfied first. In other words, there is a comprehensive requirement to
prioritize the provision of all necessary cargoes to priority sinks. This
problem will be referred to as the “unconditional sink priority” scheme.
4. The delivery of the highest priority cargoes
must be prioritized above all else. In this case, the primary objective is to
transport cargoes according to their priority level. This problem will be
referred to as the “unconditional cargo priority” scheme.
The prioritization mechanisms for each of
the aforementioned tasks depend on the nature of preferences. In the present
work, we focus on lexicographic preferences [12], which are based on the strict
ordering of priorities, whereby the underperformance of a higher-priority
request cannot be compensated by fulfilling a lower-priority one.
Consequently, the modeling of the
considered problem involves multiple stages that necessitate interactive task
formulation and/or data visualization.
At the initial stage, through an
interactive interface supported by visualization techniques, general parameters
characterizing the problem formulation can be specified:
∙ The set of nodes A and arcs W defining the route network;
∙ The set of cargo types G;
∙ The set T of node capacity values corresponding to all cargo types in G;
∙ The cost values C associated with transporting cargoes along the available routes;
∙ The throughput capacity values U for the routes.
Subsequently, a delivery prioritization scheme is selected,
and its parameters are specified, also with the aid of various visualization
techniques. These parameters serve to supplement or refine those established at
the initial stage. The specific procedure for parameter specification depends
on the chosen prioritization scheme:
∙ When employing the “sink priority for cargo” scheme, for each cargo type Gk, a subset of nodes
is selected, representing the sinks for given cargo, and ordered in accordance with
descending priority;
∙ When applying the “cargo priority for sink” scheme, for each sink node
Al a subset of cargo types
is identified and ranked in
descending order of importance for that particular sink;
∙ When applying the “unconditional sink priority” scheme, a set of nodes
is formed, comprising all sinks for
at least one cargo type, and ordered according to the overall priority of cargo
provision;
∙ When applying the “unconditional cargo priority” scheme, the full set of cargo types
is ordered in descending delivery priority.
Finally, based on the obtained optimization
results, the visualization of the resulting optimal cargo transportation plan X
must be carried out.
Each of these stages involves visualizing a
distinct set of parameters; therefore, each step requires a corresponding type
of visual representation.
The approach to constructing a visual model
based on the concept of a visualisation metaphor was originally proposed in [9]
and further developed in a number of subsequent works, including [10], in the
context of visualising graph-based models.
A visualisation metaphor is a formalised
framework for mapping the characteristics of the source model data into the
feature space of a visual model. It comprises a set of principles and rules
that establish correspondences between model elements and visual
representations, as well as between their respective attributes and visual
properties. The visualisation metaphor consists of two key components: the
spatial metaphor and the representation metaphor. The spatial metaphor defines
the general principles for embedding the visualised object into the space of
the visual model. The representation metaphor, applied within the framework of
the chosen spatial metaphor, is responsible for refining the visual
representation in such a way as to emphasise those components that are most
significant for the problem at hand. Its primary purpose is to direct the
viewer’s attention to the semantically meaningful aspects of the visual image
that require interpretation.
In the context of the problem under
consideration, the spatial metaphor defines the positioning of the route
network graph nodes within the coordinate space of the territorial map. To
construct this spatial arrangement, various algorithms for graph layout in
two-dimensional space may be employed [13].
Based on the resulting spatial
configuration, a representation metaphor is then applied to generate visual
representations of the graph’s nodes and arcs, corresponding respectively to
the points of the transport network and the routes connecting them. Within the representation
metaphor, a central role is played by the mapping between the attributes of
nodes and routes and the applied visualisation techniques.
The degree of cognitive clarity of the
resulting visual representation, as well as the usability of the interactive
interface for specifying cargo transportation plan parameters, depends
significantly on the choice and design of the corresponding representation
metaphor.
In accordance with the representation
metaphor, the visual representation of the problem under consideration
comprises a set of visual features, including the following:
∙ for nodes (in addition
to their spatial positioning determined by the spatial metaphor): shape,
colour, and size of the graphical object representing the node, as well as
supplementary graphical elements such as labels or infographic markers;
∙ for routes between nodes: primarily the colour
and thickness of the corresponding arcs, along with possible textual
annotations.
The construction of a representation
metaphor requires the establishment of a mapping between the model parameters
to be visualised (i.e., the attributes of the formal model) and the
corresponding visual attributes outlined above. Given that the number of
parameters subject to visualisation often exceeds the number of visual features
that can be employed without compromising the clarity and interpretability of
the visual image, it is reasonable to introduce multiple representation
metaphors. Each such metaphor is designed to convey specific properties of the
problem or to reflect distinct stages of the modelling process.
As noted earlier, the visualisation of the
cargo transportation planning problem is based on representing the route
network as a graph, comprising nodes and arcs enriched with attributive
information. In this representation, the nodes are geographically anchored and
correspond to specific locations on the map.
To visualise the nodes, pictograms or
geometric primitives are employed, which are connected by straight lines
representing the arcs of the graph. The colour and thickness of these lines are
used to convey key properties of the routes, such as cost or throughput
capacity. Adjacent to the nodes, infographic elements are displayed to indicate
their capacity values with respect to different types of cargo.
The overall structure of the representation
metaphor used at the problem formulation stage is summarised in Table 1. These
parameters are universal across all prioritisation schemes and are designed to
provide a clear and concise visual representation of the core characteristics
of the problem formulation.
Table 1 – General structure of the representation metaphor at
the problem formulation stage
Attribute
|
Value Domain
|
Visual Representation
|
Node identifier
|
String
|
A circle positioned at the node’s
coordinates, containing a label (letter with a number)
|
Capacity by cargo type
|
Vector of integers
|
A set of infographic elements near the
node indicating stock (green, positive) or demand (red, negative)
|
Cargo transportation cost for a route
|
Vector of integers
|
Colour intensity of the arc;
green
brightness indicates lower transportation cost; red
indicates higher transportation cost
|
Route capacity for cargoes
|
Vector of integers
|
Arc thickness; greater thickness
indicates higher capacity
|
Figure 1 presents an example of the
visualisation of initial parameters based on the representation metaphor
described above.
Figure 1 – Visualisation of initial parameters of the task of cargo
transportation plan formation
Attributes that depend on the selected
prioritisation scheme are summarised separately in Table 2.
Table 2 –
Additional attributes of the representation metaphor depending on the prioritisation
cheme
Attribute
|
Value Domain
|
Visual Representation
|
Sink priorities for a cargo
|
Ordered set
|
Infographics of different cargo types
arranged vertically by descending delivery priority to sinks
|
Cargo priorities for a sink
|
Ordered set
|
Infographics of cargo types arranged
vertically by descending priority of delivery requests for each node
|
Unconditional cargo priorities
|
Ordered set
|
Global infographic scale representing the
relative priority of each cargo type across the entire network
|
Unconditional sink priorities
|
Ordered set
|
Node fill colour reflecting the relative
priority of cargo provision for each sink
|
Let us now examine in more detail the
visualisation of parameters specific to each prioritisation scheme.
“Sink priority for cargo” scheme. An example of the visual representation of this scheme is provided in Figure 2.
The scheme considers the prioritization of cargo delivery requests across all
sink nodes. As noted earlier, for each cargo type Gk,
a corresponding subset of sink nodes is defined as
,
where the elements are ordered in descending order of delivery priority.
In this scheme, the infographic illustrates the delivery request for a specific
cargo type. The fill colour of the corresponding visual elements reflects the
relative priority of delivering the cargo to each sink node. Nodes associated
with higher-priority requests are visually distinguished using more saturated
or darker tones, enabling intuitive assessment of delivery urgency within the
transport network.
Figure 2 – Visualisation of the parameters in the scheme “Sink priority for cargo”
“Cargo priority for sink” scheme. An illustrative example of this scheme is presented in Figure 3. It
reflects the prioritisation of different cargo types within each individual
sink node. For each sink Al, a
corresponding subset of cargo types is defined as
which includes the cargo types required at node Al, ordered by descending priority specific to that sink. The
visual representation of the set
for sink Al consists of a sequence
of infographic elements, each corresponding to a specific cargo type.
The arrangement of these elements reflects
the prioritisation order, with higher-priority cargo types placed earlier in
the sequence. To enhance interpretability, elements representing cargoes of the
same type are consistently coloured. This uniform colouring aids in visually
distinguishing priority shifts across different sink nodes and facilitates
comparative analysis.
Figure 3 – Visualisation of parameters in the “Cargo priority for sink” scheme
“Unconditional Sink Priority” scheme.
An example visualisation of this scheme is presented in Figure 4. In this scheme, the
overall priority of each sink node is considered with respect to the delivery
of all cargo types collectively, without distinguishing between them. The set
includes all nodes that act as sinks for at least one type of cargo,
and is ordered by descending priority of cargo provision.
To convey this information visually, a
colour gradient is applied to the sink nodes: warm colours (e.g., orange)
indicate higher priority levels, while cool colours (e.g., light blue) represent lower priority. The
infographic elements within this visualisation depict cargo delivery requests;
however, they do not explicitly encode priority data. This approach provides a
clear and intuitive overview of the relative urgency of servicing each sink
node across all cargo types.
Figure 4 – Visualisation of parameters in the “Unconditional sink priority” scheme
“Unconditional Cargo Priority” scheme. An example of the visualisation corresponding to this scheme is shown in Figure 5.
In this approach, cargo priorities are considered globally – that is, across
all sink nodes simultaneously. The set of cargo types
,
is ordered in descending order of delivery priority and forms the
basis of the visual representation.
For visual encoding, colour saturation is
applied to infographic elements: cargoes with higher priority levels are shown
in more saturated colours along a predefined gradient scale. Additionally,
infographic elements are arranged in descending order of priority, enhancing
clarity and enabling rapid interpretation of the most urgent cargo types.
Figure 5 – Visualisation of parameters in the “Unconditional cargo priority” scheme
Finally, attributes associated with the
presentation of optimisation results are summarised in Table 3. The goal of
this visualisation is to support the analysis of the computed cargo transportation
plan by providing a clear, interpretable display. This facilitates initial
evaluation and the identification of patterns or inconsistencies that could
inform the refinement of the original problem formulation or optimisation
parameters.
Table 3 – Structure of the visualisation metaphor
for representing the cargo transportation plan
Attribute
|
Value Domain
|
Visual Representation
|
Cargo transportation plan for a route
|
Vector of integers
|
Numeric labels displayed next to each
arc, indicating the volume of each cargo type transported along the route.
|
Aggregate cargo flow
|
Integer
|
Arc thickness reflects the total cargo
flow along the respective route.
|
Degree of unfulfilled delivery requests
|
Vector of integers
|
Infographic elements representing
different cargo types, showing the volume of outstanding (unfulfilled) delivery
requests.
|
Residual throughputs
|
Integer
|
Arc colour encodes the residual
throughput, i.e., the difference between the total cargo flow along the route
and its maximum capacity.
|
An example of the visualisation of a cargo
transportation plan, obtained as the result of solving the corresponding
optimisation problem, is presented in Figure 6.
In accordance with the structure of the
visual representation metaphor described in Table 3, the infographic elements
adjacent to the nodes reflect the state of the route network after the
execution of the transport plan. Specifically, they display the volumes of
unfulfilled delivery requests as well as the remaining cargo stocks at the
source nodes.
The thickness of the arrows (arcs)
indicates the aggregate cargo flow along the respective routes, while the
numerical values of the cargo volumes for each cargo type are shown as labels
on the arcs. The arc colour denotes the residual (i.e. unused) throughput of
the route, allowing for the identification of underutilised transport links
within the network.
Figure 6 – Visualisation of the resulting cargo transportation plan
To support the implementation of the
proposed approach to the construction of visual models, a dedicated software
module has been developed. This module is integrated into a broader software
framework designed for the modelling of planning and optimisation tasks related
to cargo transportation in unmanned aerial transport systems. It functions as a
subsystem responsible for the visualisation and interactive specification of
optimisation model parameters.
The direct solution of the corresponding
optimisation problem, as formalised in expressions (1)-(2), is handled by a
separate computational module, which operates as a plug-in and implements the
algorithms described in [5].
An example of the user interface of the
visualisation module –demonstrating the use of the “Cargo Priority for Sink”
visual scheme for setting optimisation problem parameters – is presented in
Figure 7.
Figure 7 – Interface of the software module
The software module was developed using the
Python programming language and the PyQt5 framework, in conjunction with a
suite of libraries provided by the QGIS geographic information system [14]. This
combination of technologies ensures both cross-platform compatibility and
integration with spatial data processing tools.
The module enables users to load
preconfigured datasets containing information about the current state of the
route network, interactively define and modify parameters for the problem
formulation, and visualise the problem using the proposed visual metaphor.
Additionally, the system supports saving the constructed model for future reuse
or further refinement.
To assess the clarity and informativeness of the developed visual models, consider the following example. Figure 1 illustrates the visual model representing the formulation of the optimization problem. Table 4 provides the capacity values of the nodes for each cargo type used in the model’s construction; for source nodes S1 and S2 these values correspond to cargo stock levels, whereas for sink nodes D1, D2, …, D6, they represent demand volumes. Table 5 details the capacity values of the routes, which were also incorporated into the construction of the visual model under consideration.
Table 4 – Capacity of nodes by cargo type
Node
Cargo type
|
S1
|
S2
|
D1
|
D2
|
D3
|
D4
|
D5
|
D6
|
Medicines
|
10
|
12
|
-3
|
-7
|
-5
|
-4
|
-3
|
-4
|
Means of communication
|
11
|
7
|
-3
|
-2
|
0
|
-3
|
-6
|
-4
|
Food supplies
|
1
|
7
|
-4
|
0
|
-2
|
0
|
0
|
-4
|
Table 5 – Capacity of routes
Sink
Source
|
D1
|
D2
|
D3
|
D4
|
D5
|
D6
|
S1
|
5
|
3
|
2
|
5
|
5
|
3
|
S2
|
6
|
7
|
9
|
6
|
5
|
3
|
According to the representation metaphor,
the thickness of the arrows in Figure 1 corresponds to the throughput capacity
of the respective routes. For instance, the arc from node S1 to D3,
exhibits the smallest thickness, whereas the arc from S2 to D3
demonstrates the greatest thickness. This observation aligns with
the data presented in Table 5, where the throughput capacity for these routes
are 2 and 9, respectively, while the throughput capacity for other routes range
from 3 to 7.
The priority information for delivery tasks
in the context of the current problem is specified using the “sink priority for cargo” scheme and is presented in Table 6.
Table 6 – Sink priorities for cargoes
Sink
Cargo type
|
D1
|
D2
|
D3
|
D4
|
D5
|
D6
|
Medicines
|
3
|
2
|
1
|
2
|
1
|
2
|
Means of communication
|
2
|
2
|
1
|
1
|
2
|
1
|
Food supplies
|
1
|
1
|
1
|
1
|
1
|
3
|
The priority values from Table 6 were
utilized to construct the visual model shown in Figure 2. It is evident from
Figure 2 that the most intense fill colours correspond to the delivery requests
for medicines to sink D1 and food to sinkD6.
This observation is consistent with the priority data presented in
Table 6, where these requests are assigned the highest priority.
The cargo transportation plan resulting
from the solution of the optimisation problem is provided in Table 7.
Table 7 – Cargo transportation plan
Sink
|
D1
|
D2
|
D3
|
D4
|
D5
|
D6
|
Source
|
Cargo type
|
Number of transported cargo
units
|
S1
|
Medicines
|
3
|
1
|
0
|
1
|
0
|
3
|
Means of communication
|
2
|
2
|
0
|
1
|
1
|
0
|
Food supplies
|
0
|
0
|
1
|
0
|
0
|
0
|
S2
|
Medicines
|
0
|
6
|
4
|
3
|
0
|
1
|
Means of communication
|
1
|
0
|
0
|
2
|
5
|
0
|
Food supplies
|
3
|
0
|
0
|
0
|
0
|
4
|
Due to cargo shortages and the limited
capacity of the route network, certain cargo delivery requests were only
partially fulfilled. Information regarding residual cargo volumes remaining at
the sources and cargo deficits at the sinks — that is, the residual capacities
of sources and sinks — is summarized in Table 8.
Table 8 – Residual capacities of nodes by cargo type
Node
Cargo type
|
S1
|
S2
|
D1
|
D2
|
D3
|
D4
|
D5
|
D6
|
Medicines
|
0
|
0
|
0
|
0
|
-1
|
0
|
-4
|
0
|
Means of communication
|
4
|
0
|
0
|
0
|
0
|
0
|
0
|
-4
|
Food supplies
|
0
|
0
|
-1
|
0
|
-1
|
0
|
0
|
0
|
The cargo transportation plan obtained
corresponds to the one previously presented in Figure 7. Visual analysis of
Figure 7 allows for several observations. For instance, the delivery request
for communication equipment to sink D6 was
not fulfilled, despite the availability of sufficient units of this cargo at
source S2. It is evident that the arcs leading to sink
D6 are greyed out, indicating that the capacities of these routes are fully utilized.
This observation is corroborated by the comparison of data presented in Tables
5 and 7. Moreover, Table 6 reveals that the delivery requests for communication
equipment had the lowest priority among all cargo delivery requests to sink
D6.
Therefore, the proposed representational
metaphor for the visual model of the cargo transportation plan effectively
visualizes the underlying causes for non-fulfilment of certain requests—namely,
the low priority assigned to communication equipment deliveries to sink
D6 combined with the insufficient capacity of the corresponding routes. Potential solutions
to this issue include increasing the priority of communication equipment
requests for the given sink, which may result in a more complete fulfilment of
these requests, potentially at the expense of partial non-fulfilment of other
cargo deliveries. Alternatively, if feasible, increasing the capacity of the
route from S2 to D6 could also alleviate the issue.
A different situation is observed with
respect to the delivery requests for medicines and foodstuffs to sinks
D1, D3 and D4. For each of these nodes, at least
one brightly colored arc is directed toward it, indicating the presence of
unused capacity on the routes connecting the sources to these sinks. This
observation is substantiated by the comparison of data in Tables 5 and 7.
However, the infographic elements associated with these sinks indicate that the
stock of medicines and food at all sources has been depleted, a fact further
confirmed by the data in Table 8.
Therefore, the visual model allows us to
conclude that the partial non-fulfilment of transportation requests for certain
cargoes to nodes D1, D3 and D4
is attributable to cargo shortages at the sources. Resolving this
issue necessitates an increase in the overall stock levels of these cargoes
within the system.
We demonstrate that the proposed
methodology for constructing representation metaphors adheres to the
foundational principles of their design as outlined in [10], thereby enhancing
the cognitive clarity of the resulting visual models.
1.
Principle of partial visualisation.
According to this principle, only a subset of model elements and their
attributes (or, in terms introduced earlier, one representation) is visualised
at each moment of time. This is due to both the high structural and parametric
complexity of models, often exceeding the cognitive capabilities of the
analyst, and the phase of the analysis process, within which at a certain stage
there is a need to display only part of the information related to the model.
Compliance with the principle of partial visualisation is manifested in the
choice of different representation metaphors for the data corresponding to
different stages of the cargo transportation plan generation problem. This
ensures that only those properties of the model that are required for analysis
at each particular stage are visualised.
2.
Principle of injective visualisation.
According to this principle, each model attribute within one visualisation
metaphor should correspond to a unique visual feature. In other words, one and
the same visual element should not simultaneously represent two or more
different attributes, as this leads to the confusion of model properties and
complicates their correct interpretation by the analyst. Compliance with the
principle of injective visualisation is due to the fact that different
attributes of the model are visualised in different ways. For example, the
metaphors for representing problem formulation and problem-solving use
thematically coloured arrows, but since this technique is used to represent
different properties, the colour of the arrows is chosen differently. A similarity
in visualization techniques for related concepts can be noted. For example,
arrow thickness represents route capacity in the initial problem visualization,
while in the results visualization, it represents the actual cargo flow.
3.
Principle of surjective visualisation.
This principle means that each visual attribute should represent an attribute
that is significant in the context of the problem to be solved. The
representation should not include visual attributes that do not carry
meaningful load within the current analysis, as this leads to perception
overload and reduces the effectiveness of visual analysis. Compliance with this
principle is conditioned by the absence of superfluous, non-significant
attributes in visual models.
4.
Principle of subordination.
According to this principle, the visual representation of subordinate elements
should provide the possibility of unambiguous identification of their relationship
to specific superior elements of the model. A special case of realisation of
the subordination principle is the display of logical nesting of elements in
the form of the corresponding visual hierarchy. An example confirming
compliance with the principle of subordination is the correspondence of
infographic elements reflecting the capacity for different cargo types to the
nodes to which they visually relate.
5.
Principle of restructuring.
In some cases, it is possible to combine two discrete attributes into one by means
of the Cartesian product of their value areas. Application of this principle
contributes to optimizing visual perception by making more effective use of
available visual parameters. An example of compliance with the principle of
restructuring is the allocation of residual route throughput as a separate
visualised property having a composite nature — it is the difference between
the initial route throughput and the volume of the cargo flow that actually
passed through it.
The use of visual models for displaying of
a set of heterogeneous parameters that characterise the problem of forming an
optimal plan for the transportation of heterogeneous cargoes using UAVs
provides interactivity of the Decision-Maker's interaction with the optimisation
model and, in general, contributes to increasing their situational awareness
when solving the tasks of planning flight assignments. The paper proposes an
approach to building a visual model for one type of cargo transportation plan
formation problem - maximisation of cargo flow in conditions of limited
capacity of the route network, where different prioritization schemes for cargo
delivery to sinks acted as additional conditions. In the future, it is planned
to consider visual models for other types of problems, for example, the problem
of forming a cargo transportation plan optimal by the criterion of minimum time
[6], or the problem of maximising the cargo flow under the transport time
constraint. Another area of further research is the development of visual
models for the tasks of operational monitoring and management of flight task
execution.
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