## 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](https://en.wikipedia.org/wiki/Axis%E2%80%93angle_representation#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.