Dump Method

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Dumping Material on a Terrain Surface

The method used by 3d-DigPlus to dump material on a terrain surface is described below.

The Dump Settings Window allows users to control the dumping of material on the terrain surface. The description here concentrates on the method used to calculate dumped material shape and the meaning of controlling parameters.

Point Dump Algorithm

The fundamental calculation used in material dumping is the 3d-DigPlus Point Dump Algorithm or simply Dump Algorithm. This Dump Algorithm lies at the heart of 3d-Dig’s terrain reshaping and machine modeling.

This algorithm:

•takes a given volume of material

•dumps this volume at a given point on the terrain surface

•calculates the shape of this material after it "flows" over the terrain surface i.e. predicts the surface shape after dumping.

Dump repose angle

The flow of material is controlled by:

•the terrain surface shape

•the dump repose angle

The dump repose angle is an important controlling parameter of the dump algorithm. This angle is measured from horizontal. It determines the maximum angle at which newly dumped material can remain stable on the terrain surface. If the angle of material dumped on the terrain exceeds the dump repose angle, then material will move to reduce the angle.

Note that the repose angle is applied only to newly dumped material. Existing terrain shape may exist at angles steeper than the repose angle. In this case, no dumped material can remain on the terrain at such steep high points.

Discrete dump volume

A given volume of material is dumped in the following way:

•the volume of material is divided into parcels, each of approximately the discrete dump volume

•the Point Dump Algorithm is applied to dump each parcel on the terrain

The discrete dump volume is another important parameter of the dump algorithm. For most practical applications, the resulting terrain shape does not depend very strongly on the value chosen for the discrete dump volume. This is true over a fairly wide range of values for this parameter (typically 100 – 10,000 cubic meters).

Point, Line and Area Dumps

The Dump Algorithm can be applied to dump material

•at a point,

•along a "line" (i.e. similar to a terrain surface feature) or

•within an "area" (i.e. a closed polygon on the terrain surface).

This is done in the following way:

1.Divide material to be dumped into parcels with volume near the discrete dump volume as described above.

2.Dump each parcel on the terrain at the next dump point.

The next dump point is:

•The dump point (for a point dump).

•The next point selected for dumping on the terrain surface feature (for a line dump).

•The next point selected for dumping within the closed polygon dump area (for an area dump).

Next Dump Point Choice

The choice of next dump point strongly affects the operation of the line and area dumps.

For an unconstrained dump, this point may be chosen in one of three possible ways:

1.Lowest dump point

2.The next dump point is the lowest of all possible dump points. For a line dump, this is the lowest point on the terrain surface feature making up the dump line. For an area dump, it is the lowest point within the closed polygon defining the dump area.

3.Highest dump point

This is like the lowest point, except that "lowest" is replaced by "highest" in each case.

4.Random dump point

Here the next dump point is chosen "randomly". This means that all possible dump points are equally likely to be the next dump point.

Dump Constraints

Two kinds of dump constraints are applicable to the dump algorithm:

•Height constraints (dump to level, plane and surface)

•Extent constraints (dump to feature)

These will now be briefly described.

Height constraints (dump to level, plane or surface)

These constraints affect the height to which dumped material can reach. The maximum height at each point is set in one of three ways:

•A single maximum level (dump to level)

•A plane (dump to plane)

•An inner surface (dump to surface)

These three methods all work in the same way to apply the level constraint. During dumping each discrete dump volume the terrain height at the next dump point is checked against the dump level constraint. If the terrain height reaches the dump level constraint, dumping in that part of the dump line or area ceases. Material is not dumped in areas where the terrain height is set above the constraining height.

Setting a single level constraint is easy: the value is simply nominated. Setting a surface constraint simply involves nominating the inner surface to act as the constraint.

Defining a plane

Setting a plane constraint involves nominating the plane’s maximum slope below horizontal (i.e. its dip), and the direction of this maximum slope from north i.e. the plane’s dip direction. A line on the plane perpendicular to the dip direction is horizontal.

Alternatively it is possible to specify the slope of the plane in any two perpendicular directions. The first direction is termed the gradient direction, and the plane’s slope in this direction is termed the gradient. The second direction is termed the crossfall direction, and the slope of the plane in this direction is termed the crossfall. These terms are illustrated in the following figure.

Please note:

If the crossfall is set to zero, the gradient becomes the dip and the gradient direction becomes the dip direction.

Extent constraints (dump to feature)

These constraints are applied by nominating some Dump Limit Features as limiting features for a dump. These features are very similar to terrain surface feature. During dumping of each discrete dump volume, the terrain height around the limiting feature is checked for change. If the terrain height changes, dumping in that part of the dump line or area ceases.

Advancing Dump

This method of dumping applies to line dumps and area dumps. In this method, dumping starts at one end of the line dump or area dump and advances to the other end.

Dump advance can only happen if there is some way of stopping the dump on the current part of the line or area, so that that dumping can advance to the next part. This "stopping for advance" is provided by a dump constraint. The constraint is usually a height constraint, although an extent constraint can also be used.

Advancing Area Dump

An advancing area dump combined with a height constraint gives a way of filling an area up to a certain level or surface. The dumping process starts at one end of the area and advances to the other end as the area is filled. This closely models the action of many earth moving processes, for example truck dumps.

The direction of the advancing dump is defined by a Direction of Advance parameter. Conceptually an Advancing Area Dump works in the following way:

The direction of advance controls the movement of a "hidden" dump line. This dump line is perpendicular to the advancing direction. Dumping takes place along this line within the area dump. Movement of the dump line takes place when dumping can no longer take place. This is because the dump constraint has been reached all along the dump line. The dump line is then moved a short distance (related to the grid step) along the Direction of Advance and the dumping is repeated. This continues until the area is completely filled or there is no more material to dump.

Advancing Line Dump

An advancing line dump combined with a height constraint (or perhaps an extent constraint) gives a way of sequentially dumping along the line from one end to the other. The dumping process starts at one end of the line and advances point by point to the other end. Each advance to the next point occurs when the dump constraint is reached for the current dumping point on the line.

There are two possible directions of advance along the line dump i.e. End 1 to End 2, or from End 2 to End 1. The Advancing Dump calculation for a Line Dump is illustrated below: