# General¶

## Terminology¶

A model in DAVE is called a Scene. Elements/parts of a model are called Nodes.

So Nodes are placed in a Scene to model something.

Groups of nodes can be saved as an Asset. This is then a re-usable building block.

## Axis systems¶

Axis systems are right-handed.

In the global axis system the Z-axis points up.

The mean sea-surface is defined as Z=0

## Units¶

The default unit system is m, kN, mT (metric tonne). G and RHO are defined accordingly.

## Rotations¶

Unfortunately there is no standard way of defining rotations in 3D.

DAVE uses a rotation vector to represent rotations. This means that the rotation is defined as a vector with three components (rx,ry,rz). The magnitude of the vector is the rotation in degrees. The axis of rotation is the direction of the vector.

Some examples:

`(0,0,90)`

: A rotation of 90 degrees about the Z-axis`(0,-10,0)`

: A rotation of -10 degrees about the Y-axis`(10,10,0)`

: A rotation of sqrt(10^2 + 10^2) about the (1,1,0) axis.

Hint: If euler angles are needed then axis systems can be stacked to obtain the same result.

### 2D rotations¶

The following 2D rotations are available: tilt_x, tilt_y, heel, trim, heading and heading_compass. These are derived from the projection of one of the local axis onto the global axis system. For example the tilt about the x-axis is derived from the z-component of the y-axis.

Example: A 3d rotation of (5,0,0) will give a heel of 5 degrees and a tilt_x of 8.7% A 3d rotation of (0,0,120) will give a heading of 120 degrees and a heading_compass of 330.