Resources Allocation
The resources allocation is a function that identifies an influence zone
of a center or a point object. This center, source or receptor, has a demand
value associated. This demand value might correspond, for instance, to the
total power that an electrical substation can afford, or a number of students
that can go to a certain school.
For this type of application, the parameters that have to be modeled in the
network are the following:
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The center has to correspond to a point object and has an attribute that can be
used as a demand (application dependent).
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Each linear representation has to have a demand value associated, which is
equivalent to the center demand. This demand value can be obtained from an
object attribute for each linear representation.
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As in the shortest path application, the flow
directions in the network must be modeled. These flows are specified by the
positive (from the initial node) impedances (costs) and negative ones (from the
final node). Impedance values equals to -1 indicate a blocking in the
respective direction. The impedance can be modeled using its own lines distance
or any object attribute.
The resources allocation can be computed from the reference object, in this
cases the flow directions considered are the ones that come from the source.
For instance, the electrical power produced in an electrical power plant is
distributed to the consumers through a network. The electrical power plant is
the center and concentrates the available energy. The consumers, located
throughout the network, creates a demand to be allocated. In this case, the
resource available, electrical power, has to be transported through the
network, starting in the power plant, to satisfy the consumers demand.
In another situation the flow directions considered has to be the ones arriving
to the center. As an example, imagine the students situation, they live
throughout a streets network and they have to move towards the school. The
school has a total capacity, which works as a demand, and the demands of each
linear element in the network corresponds to the number of students in each
part.
In the network modeling the impedance item is fundamental. Impedance is the cost
for moving around the network. In the school example, the impedance could be
the time that the student spent to arrive in the school. Each linear element in
the network has impedances associated in both of the flow directions.
Executing a resource
allocation:
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activate the IL of the network model in the "Control Panel";
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verify if the Current Infolayer's name corresponds to the active
layer in the Object area:
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click on Select... to select the point object in the
window. The objects name selected is then presented in the Name field
and the object attributes listed in Demand Attributes. Click over
a demand attribute and its value is presented in the Demand
field. The selected attribute has to be of the numerical type.
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click on Allocate: and select between Arriving Node or Leaving
Node to the considered flow direction. In the school example it would
be "Arriving Node", because the students move towards the school. In the
electrical power plant case serving consumers in the network, the "Leaving
Nodes" should be selected.
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in the Network Parameters Cost area:
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click on Impedance
if one wants or not to have the impedance values computed again. If the
processing is repeated and the cost values are the same, this item can be
unmarked, forcing the system to use the data stored in the database without
computing them again.
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select if the impedance will be an Object Attribute or a Distance
among the nodes in the network. Notice that in the distance case, the
attributes list of the impedance stay deactivated;
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type the Maximum Impedance
value. The program ends when the maximum impedance is reached or when the
demand parameter of the selected center is reached;
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choose in the category list the one that belongs to the linear objects
that are represented in the network;
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Select the impedance attribute to be used;
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Activate or deactivate the demand attribute for each linear element. Select the
demand attribute of the linear elements . - Press the Apply button. -
The "Description" button lists the obtained results.
See also:
Digitalization of Maps
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