The GRASS Program

The Grass-mower Routing and Scheduling System (GRASS) has been designed to provide an interface with the data for each of the individual locations mown by City Care, the types of mowers available, and all the problem-specific parameters linked with the heuristic. In addition, it houses the model for estimating grass-growth and the routing and allocation heuristic used for creating the daily routes. It also enables the users to plot each mower operatorís route on a map of Christchurch, and allows easy updating of the grass lengths for every location mown in a day.

 

The Data
Grass Growth Model
Daily Process
Viewing the Map of the Routes Constructed
Breakdown Contingency
Absent Employee(s)
Preferences

The Data

The GRASS program provides an easy-to-use interface with several text files in which all the data required for the construction of the daily routes is stored. Obviously, if the user were to open these files manually to try and modify some of the data, it would be a very long and arduous process. Therefore, forms such as the one shown below have been designed to allow easy additions to, deletions from and modifications to the data set.

 

Location Information

Figure 1. Location Information Form

 

Grass Growth Model

The code for the entire grass growth model is housed within the GRASS program, and all that the user is required to input are four weather readings for each day. Before the mowing rounds for the following day are created, the user is required to enter estimates of each of these readings for that day, and correct the estimates they made the previous day. The grass growth for each location is estimated as a function of these four weather variables, the growth rate of the grass at that particular location, and whether or not that location is irrigated. How urgently a location requires mowing is calculated as a function of the estimated grass length at that location if it were not mown the following day.

 

Weather Form

Figure 2. Enter Weather Information Form

 

Daily Process

Daily Process Form

Figure 3. Daily Process Form

 

Each day, a particular process must be followed in order to construct the mowing rounds for the following day. After the corrections and estimations of the weather details have been provided, the next step is for the locations that were mown on the previous dayís mowing rounds to be checked off. This resets the grass length for these locations to the mown length (20mm in the City Care case). Also on the Route Completion form, shown below, the user can enter the time it took for each individual location to be mown, which updates the expected mowing time for that location stored in the data.

 

Round Completion Form

Figure 4. Check Off Locations Mown Form

 

Viewing the Map of the Routes Constructed

The final step in the daily process is to press the Solve button on the Daily Process form, which creates the mowing rounds for the following day. The rounds are automatically exported to a timesheet template in Microsoft Excel and printed for the operators. Also, the user is able to view a map of Christchurch onto which the routes are overlaid, so that if need be, each operator can be assigned to a route in the area they know best. The route number in the graph key can be clicked, which automatically brings up the Route Completion form for that route.

 

View Route Diagrams Form

Figure 5. View Route Diagram Form

 

For each mowing round shown on the map of Christchurch, the locations mown within the scheduled round time (i.e. eight hours) are joined by a thick line. Those mown after eight hours are joined by a thin line.

 

Breakdown Contingency

If an operatorís mower were to break down in the middle of a round, the GRASS program contains an option for creating a new route for the number of hours left in the day. The route constructed may be for any one of the types of mowers available, depending on to which mower the most urgent locations have been assigned. If the new mower assigned is the same as the one that broke down, the new route is likely to contain most of the locations that were not mown already that day.

 

Single Route Form

Figure 6. Find a Single Route Form

 

Absent Employee(s)

If an operator were to be absent from work before the rounds have been assigned, or more rounds are created than there are employees available, then the GRASS program can rank the rounds in increasing order of priority, and therefore decide which is the best route to leave out of the rounds that day.

 

Route Priorities Form

Figure 7. Daily Route Priorities Form

 

Preferences

As with any application, the GRASS program has many options concerning such things as where the data and output files are stored, what the contractual requirements are (e.g. the dates of the cricket season), what length the grass is cut to, the length of the routes to create, and more technical options such as how long to run the route creation procedure. Each of these options can be adjusted in the Preferences section of the program, through a standard Windows-style multi-tab form.

 

Preferences Form

Figure 8. Preferences Form

 

 

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Paul Stewart & James Tipping, November 2002