Curves and Surfaces
The majority of entities supported in PolyCAD are curve or surface type entities. Given the growth of the use NURBS based entities certainly for representing hull surfaces, effective manipulation of these entities is one of the most important factors in providing an effective and efficient design tool. PolyCAD optimises the display of these elements, and hence the operational speed of software, by keeping a display list for each complex entity and updating them only when there is a change. With each entity having their own edit mode, locking the geometry others unless relationally linked, manipulation becomes more focused and the user no longer needs to worry if other entities will be accidentally affected by any erroneous selection. To further optimise the editing process, entities can be hidden, shown as only bound boxes, displayed in wire frame or rendered. In addition, the viewer employs adaptive degradation which maintains rapid updates of the model environment when manipulating the view.
All editable entities support control polygon points used to manipulate the geometrical definition of the element. PolyCAD primary is to provide effective ways manipulating control points so that the user can realise their design. To these ends, when manipulating control points, the user has the choice of using the SnapToGrid, SnapToObject and Enhanced 3D Editing features. These tools provide the means to accurate manipulate control points using the mouse with respect to accurate dimensions within the model enviroment, to other entities and to contraint reducing the number directions a point can be edited in.
In version 8, the OpenGL graphics system underwent a major upgrade to improve the editing experience. The biggest change is that the manipulation of the viewer has change from being based around the transformation matrix to a camera based system. This allows much more flexible view manipulations and now makes it possible to allow editing in perspective views. All of the old functions are still available but the camera now, but default, rotates about a look at point rather that the centre of the model. The view can now rotate about the edit location and is particular effective if used with zoom to selection. The viewer functions are summaries as follows.
|Select and View|
|Select entities. Press F2 to edit.|
|Interactive Zoom in and out on the Left mouse button. Roll the mouse wheel for the same effect. Can also be set as the middle mouse button/mouse wheel click behaviour depending on the settings in PolyCAD Options.|
|Pan the screen. Can also be set as the middle mouse button/mouse wheel click behaviour depending on the settings in PolyCAD Options.|
|Rotates the view either at the centre of the model or at the focal point of the screen. Can also be set as the middle mouse button/mouse wheel click behaviour depending on the settings in PolyCAD Options.|
|Zoom to display the selected entity.|
|Zoom area described by the interactively drawn rectangle.|
|Zoom to the previous view.|
|Zoom in by 10%.|
|Zoom out by 10%.|
|Toggle between parallel and perspective projections.|
|View the model in the YZ plane/Hull Cross Section Plane.|
|View the model in the XY/Plan/Waterline plane.|
|View the model in the XZ/Elevation/Buttock plane.|
|Display the selected entities or, if none selected displays all entities, as detailed wire frame.|
|Display the selected entities or, if none selected displays all entities, as shaded surfaces if appropriate for the entity.|
|Hides the selected entities or, if none selected hides all entities.|
|Selects all visible entities|
|Deselects all entities|
|Toggles the selection of all displayed entities.|
When viewer complex or rendered models, the increased time required to update the screen can make positioning of the viewer difficult. In these situations, the adaptive degradation can be used to temporarily simplify the model to bounding boxes for the duration of the view manipulation. Adaptive degradation settings are found in the PolyCAD Options Panel -> Adaptive Degradation.
The axis icon assists in understanding the orientation and origin of the model in the viewer. It can be displayed located at the model origin, in the bottom left corner of the view or turned off in PolyCAD Options Panel -> Axis Icon.
The grid assist in understanding the orientation and scale of the model. It can also be used to locate control polygon points when SnapToGrid is enabled. Options for controlling the grid are found in PolyCAD Options Panel -> Manipulation Options.
Colors are extensively used for highlighting features while manipulating entities. While each entity has its own color, in edit mode specific colors are used to define parts of the editing framework and control polygon. These colors are set and control in PolyCAD Options Panel -> Colors.
As the major aim of PolyCAD provide the user with the ability to achieve a higher level of accuracy and quality in the geometric definition, curve and surface analysis tools are provided to give feedback on shape. For curves the a porcupine plot displays the magnitude and direction of curvature, while in surfaces, gaussian and mean curvature can be displayed using various color models which highlight different qualities in the curvature values. These color models are specified in PolyCAD Options Panel -> Surface Curvature Shading Model.