# 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`(Free, 0, 0)`

: Frame is free to rotate about the x-axis`(Free, Free, 0)`

: Axis system is free to rotate about any axis with z=0. The effect of this is hard to visualize, setting this will issue a warning in the Gui.`(10,10,0)`

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

If Euler angles are needed then axis systems can be stacked to obtain the same result: To define subsequent rotations about different axis stack Frame-nodes on top of eachother. For example to model a rotation of 20 degrees about the z-axis (yaw) and rotation of 5 degrees about the y-axis (pitch) simply consider the following:

Create a

`Frame`

for the yaw. Set the rotation to (0,0,20)Create a

`Frame`

and place it on the yaw-frame. Set the rotation of this axis system to (0,5,0).

## 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.