CST2013: Coordinate Systems

For structure modelling, two coordinate systems are available: global and local coordinates. At any time, only one particular coordinate system is active. Moreover a coordinate system can be attached to a solid. This solid will own a local solid coordinate system from then on, see below for more details.

When the global coordinate system is active, all structure definitions will be performed in x/y/z coordinates. You cannot change the orientation of these coordinate axes.

To define a structure that is not aligned with the axes of the global coordinate system, (e.g., a brick) you may first create the shape in global coordinates and then apply a transformation. However, a more flexible way is to define a local coordinate system before starting the shape creation and then create the shape in this local coordinate system. Such local coordinates are also referred to as the working coordinate systems (WCS).

In general, a local coordinate system (or WCS) is defined by the orientation of its u, v and w axes and the position of its origin. Because the coordinate axes still need to be orthogonal to each other, it is sufficient to define the orientation of the w and u axes.

Activating and Deactivating Local Coordinate Systems

The global or local coordinate systems activity may be toggled by choosing the option: Modeling: WCSLocal WCS. The same option may also be chosen from the toolbar or from the context menu.

As soon as the WCS is activated, it is displayed in the structure view showing the u, v and w axes. The working plane will then be centered at the origin of the WCS and aligned with it’s uv plane. Coordinates of picked points, edges and faces are displayed in the local coordinate system.

Defining and measuring the Parameters of the Local Coordinate System

The parameters of the WCS may be directly entered from the Modeling:WCSLocal WCSLocal Coordinate System Properties dialog box. Here, you may specify the origin of the coordinate system and the orientation of its w and u axes. This option is the most general way to define a local coordinate system. However, the WCS parameters are more frequently changed by the  ”align operations” function described below.

The information concerning the relative position and orientation of the local coordinate system in respect of the global coordinate system is also shown in this dialog box.

Store Current WCS

The currently active local coordinate system may be stored for later use in the  Modeling:WCSFix WCSStore Current WCS dialog box. Please define a specific user name for the coordinate system and activate it later by selecting Modeling:  WCSFix WCSRestore Selected WCS, Restore from the context menu orby double-clicking on the corresponding WCS in the navigation tree.

Move and Rotate Local Coordinates

The origin of the local coordinate system may be moved by a fixed translation vector either in local or global coordinates. The orientation of the local coordinate system may be rotated by a certain angle around one of its axes. This can by achieved by using the  Modeling:  WCSTransform Local Coordinates dialog box. Rotating around u, v or w by 90 degree may be performed by pressing Shift-U, Shift-V or Shift-W respectively.

Align the local coordinate system

To align the WCS with edges, faces or points, press "W" or choose  Modeling:  WCSAlign WCS.

Depending on the most recent selection one of the following steps will be performed:

If nothing is selected, you will enter the interactive WCS alignment mode.

If three points, only one point, an edge or a face is selected, one of four below WCS alignments will be performed.

If a face and an edge are selected and the edge is directly connected to the face, the WCS will be moved onto the middle of the edge. The u-axis will be aligned parallel to the edge in the chosen point, the normal of the WCS will be aligned parallel to the normal of the face in the chosen point.

Align WCS with Selected Face

In many cases, the orientation of the local coordinate system must be aligned with planar faces from within the structure. This common operation is supported by the  Modeling:  WCSAlign WCSAlign WCS with Selected Face operation that may be selected after picking a planar face. This operation will align the uv plane of the WCS with the surface of the most recently selected planar face and move the WCS to the center of the face.

 If the picked face is not planar, the WCS will be moved to the closest point on that face relative to the current WCS. The normal of the WCS will be set to the normal of the face at the chosen point.

Align WCS with Selected Edge

The orientation of the local coordinate system’s u-axis may be simply aligned parallel to the most recently picked linear edge by choosing the Modeling:  WCSAlign WCSAlign WCS with Selected Edge operation. If the selected edge is connected to any face, the normal of the WCS will be adapted to the normal of one of the adjacent faces. The origin of the local coordinate system will be moved to the center of the picked edge.

Align WCS with Selected Point

The origin of the local coordinate system may be easily moved into the most recently picked point by choosing the Modeling:  WCSAlign WCSAlign WCS with Selected Point operation.

Align WCS with 3 Selected Points

The origin of the local coordinate system may be easily moved into the three most recently picked point by choosing the Modeling:  WCSAlign WCSAlign WCS with 3 Selected Point operation. The first picked point defines the origin. The second and third points the u and v axis.

Align WCS with Global Coordinates

The position of the WCS will be changed to the position of the Global Coordinate System. In other words, a reset of the WCS into its origin position.

Fix WCS

The position of the WCS is stored in absolute coordinates

Use the Context Menu to Define the Local Coordinate System

All the operation described above may also be accessed from within the context menu in the modeler mode, if no shape is currently selected.

Use the Ribbon to Define the Local Coordinate System

Besides the context menu, the operations for changing the local coordinate system may also be accessed from the Ribbon tab Modeling: WCS :

Shortcut Keys to Align the Local Coordinate System

The most important shortcut key in combination with the local coordinate systems is the "W" key. The main view must be activated (by clicking into it) in order to use this shortcut. After pressing the W key, the local coordinate system will be aligned with the most recently picked point, edge or face (See Align WCS with Selected Item above.)

Local Solid Coordinate System (SCS)

Application:

For features which depend on the orientation of a solid (like anisotropic materials), it is useful to define a local solid coordinate system which transforms with solid transformations and which is copied when the solid is copied within a transformation.

Definition a SCS:

A local solid coordinate system is defined by attaching the currently active (global or local) coordinate system to a selected solid. This can be done in the context menu of the selected solid (Local Solid CoordinatesAttach Active WCS) or via Modeling: ToolsShape Tools Local Solid CoordinatesAttach Active WCS. Likewise, with multi-selection, an active coordinate system can be attached to more than one solid in one go.

Change a SCS:

The local solid coordinate system can be changed by simply attaching a new WCS to the solid.

Preview all SCS:

Via the context menu (Local Solid Coordinates View SCS for all solids) or the ribbon tab (Modeling: ToolsShape ToolsLocal Solid CoordinatesView SCS for all solids) the preview of all defined solid coordinate systems can be activated (or deactivated). Likewise you can switch on or off this preview in the View Options dialog box (View: OptionsView Options).

When the preview of all solid coordinate systems is selected, the appropriate systems are drawn in a shaded style with the axis labels u', v', w'  for each solid owning a local solid coordinate system.

Preview selected SCS:

Via the context menu (Local Solid Coordinates View SCS for selected solids) or the ribbon tab (Modeling: ToolsShape Tools Local Solid CoordinatesView SCS for selected solids) the preview of solid coordinate systems can be activated (or deactivated) for selected solids. Likewise you can switch on or off this preview in the View Options dialog box (View: OptionsView Options).

When the preview of solid coordinates systems of selected solids is selected, the appropriate systems are drawn in a shaded style with the axis labels u', v', w'  for each selected solid that owns a local solid coordinate system. When only one single solid is selected, the solid description contains a line "Local SCS" which states "active" when a local SCS is defined (and previewed) or "not defined" when no local coordinate system is attached to the selected solid.