# Axes

This feature enables new user-defined axes systems to be specified e.g. to specify an inclined roller support, to assist in interpretation of results, or to specify the construction grid. Axes systems may be Cartesian, cylindrical or spherical.

## Definition​

A user axes set is created by specifying the following:

### Name​

Used as a convenient way of identifying an axis.

### Type​

Axes can be Cartesian, cylindrical or spherical.

### Origin​

The location of this axis system in the global axis system.

### X vector​

A vector, defined in the global axis system, in the direction of the local x-axis.

### XY vector​

A vector, defined in the global axis system, which lies in the local xy-plane.

An example of the definition and application of user-defined axes is given below.

The user axis origin coordinates are thus defined as $(x, y, z)$ above. The rotational orientation is defined in terms of a vector along the positive $x_n$-axis and a vector in the $x_ny_n$ plane. These two vectors are defined in the laterally shifted axes system shown above.

E.g. consider the simple case of rotation about the $y_n$ axis alone to give an inclined plane for a support

The $\mathbf{x}$ vector could be expressed as $(a, 0, 1)$. This defines the position of the $x_n$ axis.

The rotation of the user axis system about this axis must be defined by specifying any $\mathbf{xy}$ vector in the $x_ny_n$ plane, apart obviously from the $x_n$ axis itself. In our case here, there is no rotation and the vector can be taken as $(0, 1, 0)$ i.e. the $y_n$ axis.

## Modify axis​

The modify axis dialog is used to modify an axis set. This dialog can be activated from the Axis definition dialog and modifies the axis definition. To apply multiple transformations use this dialog to apply the modifications one after the other.

### Translate by / rotate by​

The user can choose to modify the axis either by translating along one of the current axis directions or rotating about one of the current axes by the amount specified.