When presented with a spatial problem, we have seen that the SPARTA system delivers solutions as sets of alternative addresses, generated from a number of declarations of objects and constraints between them. These addresses are easily presented to the us er as a map.
The integration of functions such as that of noise level against distance from the road source enables the reasoning technique to be applied to data stored in the tesseral GIS. From this it follows that we are able to reason about areas related by their acoustic level, and obtain answers to questions such as "where are the sites suitable for housing development if a major road is constructed through this area?''
We can also reason about the effects of mitigation of noise levels by erection of barriers at suitable sites - ``How high and where should a barrier be to bring this area into noise level A'' and ``With this barrier at this site, where are the alternative sites for a hospital'. This is accomplished by solving the appropriate acoustic equation with corrections applied for the barrier information.
We illustrate this functionality here. We define a problem in which objects are declared to represent a road, which generates noise, areas which are suitable for building, and areas which have other features which are relevant to the problem. The area which is sought for a development site must be within 5 km of the road. We then apply constraints which are couched in terms which define the restrictions we are seeking, and which yield all the addresses which fulfil the constraint.
The level of noise at a particular point along a road is a function of its distance from the source of the noise. Solving the equation for a given noise level delivers the required distance from the source at which this level is found. This distance is then used to calculate the limits for the various levels of noise, where development would not be allowed to proceed.
For example, assuming no unusual circumstances (such as limited angle of view or steep gradient), traffic flow of 1700 vehicles/ hour at a speed of 91km/h, 10 percent of which are heavy vehicles, then the distance from the noise source at which category A noise level of less than 55 dB(A) applies is calculated to be 673 metres. This distance is converted to the appropriate number of tesseral tiles according to the scale, for use as the radius of a circle as described in the overview to this section, and forms part of a constraint.
The tesseral map of the Wirral peninsular as shown in Figure 3 is declared in the SPARTA system as:
object: noiseA
object: water location
object: rural location
object: urban location
object: M53 location
object: forDevelopment
and the constraints:
constraint: forDevelopment notWithin urban
constraint: forDevelopment notWithin M53 offsetBy circle radius1
where radius1 is the distance calculated as above.
constraint: forDevelopment within M53 circle radius2
where radius2 is 5km converted to tesserals.
Solutions after applying the first constraint are the tesseral addresses of all the area which is not greenbelt land, and this set of addresses is now associated with the object forDevelopment. Applying the second constraint further prunes the set to include only those which fall outside the acceptable noise level generated by the road, and the third constraint delivers the final solution of all those addresses which are within 5 kilometres of t he road. These addresses are displayed as a map, thus providing the user with visual information which supports the planning process.
With the incorporation of functions to calculate the effects of introducing mitigating measures for the acoustic effects of the road, such as the erection of barriers close to it, the system is able to present the user with an alternative map of suitable areas. For example, with the erection of a 3.5 m high noise insulation barrier situated 5.0 metres from the edge of the carriageway, the distance at which noise level category A occurs is reduced to 55 metres. The new distance is input and the new map displayed.
Inputting values of the decibel levels for the other noise categories enables the users to produce a map of the noise levels around the road.