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<< Click to Display Table of Contents >> Using Approximate and Virtual Vertical Alignments |
  
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<< Click to Display Table of Contents >> Using Approximate and Virtual Vertical Alignments |
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In the preceding topics procedures were described for creating Roads on Terrain. The the Vertical Alignments for the three Modes of Operation had the following characteristics:
•Main Haul Roads. The Main Haul Roads described all had a horizontal alignment which followed an existing surveyed road on the topography. Hence the Vertical Alignment required already exists in the surveyed topography. The Roads Vertical Alignment was placed to follow the topography in the longitudinal section along the Horizontal Alignment. In this case the topography along the line of the Horizontal Alignment and the Vertical Alignment are coincident or close to within a small tolerance.
•Excavation Access. In the examples in previous topics the design surface for the excavation incorporated a high wall ramp. The Excavation Access Horizontal Alignment ran down the centreline of the ramp. The Vertical Alignment followed this design ramp. Consequently as each lift is excavated, the Vertical Alignment in the Active Portion of the Excavation Access Road was consistent with the topography exposed for that lift.
•Dump Access. In the examples in previous topics the design surface for the dump incorporated an access ramp. The Dump Access Horizontal Alignment ran down the centreline of the ramp. The Vertical Alignment followed this design ramp. Consequently as each lift is dumped, the Vertical Alignment in the Active Portion of the Dump Access Road was consistent with the topography formed for that lift.
In these examples the three-dimensional road system formed by the Excavation Access, Main Haul and Dump Access Roads follows the topography exactly. This road system is the one used to determine truck speeds during simulation. When such a road system is used simulation trucks will be animated and will appear to follow the roads running along the topography.
Trucks always follow the Horizontal Alignment during animation, and they always appear on the topography regardless of the gradient of the topography at any point. Internally however simulation always takes place on the Vertical Alignment. In the examples in previous topics, where the Vertical Alignment and topography are consistent this relationship is intuitive and the simulation appears quite realistic. However it is important to understand that internally during simulation trucks run on the Vertical Alignment not the topography. Trucks will always appear on the topography but the gradients used in the simulation will be those from the Vertical Alignment.
In detailed simulation it will typically be the case, as in the examples of the previous topics, that access ramps will exist in design surfaces and Vertical Alignment and topography will be consistent. However there are several situations where it is convenient and advantageous to have a Vertical Alignment which is either fully or partially independent of the topography. These situations are referred to as Approximate Vertical Alignments, and Virtual Vertical Alignments.