Creating and Manipulating Geometry

Geometry Creation

There are modal operators provided for the creation of new geometry. In the Create menu, you can select from a variety of shapes. Once a geometry creation operator has been selected, geometry may be interactively created with the mouse. All operators respond to the following sequence: left mouse button down, left mouse button down & moved (motion), left mouse button up. The following geometric entities may be created: 

  • Spheres
  • Cylinders
  • Cones
  • NURBS Curves (second degree)

The Sphere entitiy is defined by one full cycle of left mouse button (LMB) down, LMB down & motion, LMB up. The Cylinder and Cone entities require two full cycles, the first defines the circle for their base and the next sequence defines the height vector. To create a NURBS curve, click the left mouse button to define the starting point of the curve. Move the mouse and click left mouse button for each control point location. Double click to define the end point of the curve.

Geometry Selection

In the Selection menu, you will find four Geometry Selection Operators which are modal operators associated with the view. There are four selection operators provided: Select By Single Click, Select By Window, Select By Polygon and Select By Polyline.

  • Select By Single Click

    Select By Single Click is the default pick mode. This type of selection operator selects and highlights the HOOPS geometry that is nearest to the coordinate of a Windows mouse click.

  • Select By Window

    Select By Window selects and highlights all the specified geometry types in a user defined the window. The window is defined by a sequence of events using the left mouse button: down, down and motion, up. On the mouse up event, the selection calculation is performed and the selected geometry is higlighted.

  • Select By Polygon

    Select By Polygon selects and highlights all the specified geometry types within a user specified polygon. The polygon is defined by a sequence of events using the left mouse button: down, down and motion, up, down, down and motion, up and so on. These motions are continued until all side of the polygon are describe. To end the process, double-click the left mouse button. On the double-click event, the selection calculation is performed and the selected geometry is higlighted.

  • Select By Polyline

    Select By Polyline selects and highlights all the specified geometry types that intersect a user define polyline. The polygon is defined by a sequence of events using the left mouse button: down, down and motion, up, down, down and motion, up and so on. These motions are continued until the polyline is completely defined. To end the process, double-click the left mouse button. On the double-click event, the selection calculation is performed and the selected geometry is higlighted.

To create a selection list of multiple entities hold down either the Shift or Ctrl key while using either of the Selection Operators. The Modeling Transform Operator operates on the geometry in the current selection list.

You can delete all the objects in the active view's selection list by pressing the [DELETE] key.

In Tools->Options, the selection mode can be changed from the standard "analytical" selection of HOOPS to a visibilty based selection model. This option causes selection to choose only one object, the visible, front-most one. It is expected behavior for this model to select invisible geometry if back-face culling is on.

Clash Detection

From Selection menu, the "clash detection" option can be activated once you have selected an object. When this option is on, HOOPS will detect and highlight objects that intersect with the selected object as you move it around the scene.

Moving Geometry

In the Selection menu, two operators are provided for moving objects around the scene:
  • Object Translate
  • Object Rotate

The user can either move an object around in the view plane or rotate an object about its centroid.  If the shift key is held down while moving geometry with the translate operator the selected geometry will be moved in/out the window z-plane.  Both operators operate on objects in the selection list and work only when the selected objects are segments (you control the selection level with the right click menu).  However if no object is currently selected, the object which is currently under the mouse cursor is temporarily selected for the operation. The translate operator is designed to work independent of the size of the selection set.  However, the rotate operator is designed to only work when there is only one object in the active view's selection set.

In addition to using an explicit operator to manipulate geometry it is also possible to active "handles" on a geometry piece by either double clicking on an object while the orbit operator is active or by using the right-click menu with Manipulator->Activate. By clicking and dragging on the handle geometry users can intuitively translate and rotate objects. Using the Manipulator menu, individual handles can be activated/deactivaed or all handles can be removed from the scene at once.

2.5.5 Cutting Sections

From the Create menu, you can insert a two-sided or three-sided Cutting Section. These cutting sections are a more advanced form of cutting plane, where the cutting planes intersect and affect each other. The cutting sections can be manipulated via the manipulators, like normal cutting planes.

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