PlaneGeometryIntersection Class 
Class for computing the intersection of geometry with a plane.
Preview Feature: this class is fully supported and can be used in Open Inventor applications. Being tagged as a Preview Feature just means that the implementation is still subject to API changes and adjustments based on feedback from early adopters. Please be also aware that source compatibility might be broken regardless of the Open Inventor compatibility changes policy due to our commitment to bring needed changes to be sure the specifications of this Preview Feature match the expectations of our customers.
Namespace: OIV.Medical.Nodes
The PlaneGeometryIntersection type exposes the following members.
Name  Description  

PlaneGeometryIntersection 
Recompute the intersection.
Recomputes the intersection boundary(s) based on the current #scene and #plane.
Normally used when the #automatic field is set to false. Useful when the goal
is simply to compute the intersection. Also useful if recomputation is too
slow. For example, to defer recomputation until the user has finished moving
the clip plane.
Returns 0 if successful. Any other value means that an error occured during the
computation and the geometry may not be valid.

Name  Description  

AddChild  Adds a child as last one in group.  
AffectsState  Returns true if a node has an effect on the state during traversal.  
Callback  (Inherited from SoSeparator.)  
ClearCacheList  (Inherited from SoSeparator.)  
Copy  Calls Copy(false). (Inherited from SoNode.)  
Copy(Boolean)  Creates and returns an exact copy of the node.  
CopyFieldValues(SoFieldContainer)  Calls CopyFieldValues(fc, false). (Inherited from SoFieldContainer.)  
CopyFieldValues(SoFieldContainer, Boolean)  Copies the contents of fc's fields into this object's fields.  
Dispose 
Releases all resources used by SoDisposable.
(Inherited from SoDisposable.)  
Distribute  (Inherited from SoNode.)  
DoAction  (Inherited from SoSeparator.)  
EnableNotify  Notification at this Field Container is enabled (if flag == true) or disabled (if flag == false).  
Equals  Determines whether the specified Object is equal to the current Object. (Inherited from Object.)  
FieldsAreEqual  Returns true if this object's fields are exactly equal to fc's fields.  
FindChild  Finds index of given child within group.  
Get  Returns the values of the fields of this object in the Open Inventor ASCII file format in the given string.  
GetAllFields  Returns a list of fields, including the eventIn's and eventOut's.  
GetAlternateRep  This method is called by actions to allow the node to provide an "alternate representation" when appropriate (typically depending on the action type).  
GetBoundingBox  (Inherited from SoSeparator.)  
GetChild  Returns pointer the child node with the given index.  
GetEventIn  Returns a the eventIn with the given name.  
GetEventOut  Returns the eventOut with the given name.  
GetField  Returns a the field of this object whose name is fieldName.  
GetFieldName  Returns the name of the given field in the fieldName argument.  
GetFields  Appends references to all of this object's fields to resultList, and returns the number of fields appended.  
GetHashCode 
Overrides GetHashCode().
(Inherited from SoNetBase.)  
GetMatrix  (Inherited from SoSeparator.)  
GetName  Returns the name of an instance.  
GetNumChildren  Returns number of children.  
GetPrimitiveCount  (Inherited from SoSeparator.)  
GetRenderEngineMode 
This override is mandatory to specify the custom node's render
engine mode. If not overridden, a warning message will be displayed.
(Overrides SoNodeGetRenderEngineMode.)  
GetRenderUnitID  (Inherited from SoNode.)  
GetShape 
Get the shape node that contains the computed vertices and indices.
Returns null if no shape has been computed yet.
In curve mode this is an SoLineSet. In polygon mode this is an SoIndexedFaceSet.
In both cases the vertices are in the shape node's attached SoVertexProperty
node's 'vertex' field.
The application must not modify these nodes.
 
GetStringName  (Inherited from SoBase.)  
GetType  Gets the Type of the current instance. (Inherited from Object.)  
GLRender  (Inherited from SoSeparator.)  
GLRenderBelowPath  (Inherited from SoSeparator.)  
GLRenderInPath  (Inherited from SoSeparator.)  
GLRenderOffPath  (Inherited from SoSeparator.)  
GrabEventsCleanup  (Inherited from SoNode.)  
GrabEventsSetup  (Inherited from SoNode.)  
HandleEvent  (Inherited from SoSeparator.)  
HasDefaultValues  Returns true if all of the object's fields have their default values.  
InsertChild  Adds a child so that it becomes the one with the given index.  
IsBoundingBoxIgnoring  Used by BoundingBoxAction to known if bounding box computation should be ignored or not.  
IsNotifyEnabled  Notification is the process of telling interested objects that this object has changed.  
IsOverride  Returns the state of the override flag.  
IsSynchronizable  Gets the ScaleViz synchronizable state of this object.  
Pick  (Inherited from SoGroup.)  
RayPick  (Inherited from SoSeparator.)  
recompute 
Recompute intersections and (if requested) boundaries.
 
RemoveAllChildren  Removes all children from group.  
RemoveChild(Int32)  Removes child with given index from group.  
RemoveChild(SoNode)  Removes first instance of given child from group.  
ReplaceChild(Int32, SoNode)  Replaces child with given index with new child.  
ReplaceChild(SoNode, SoNode)  Replaces first instance of given child with new child.  
Search  (Inherited from SoSeparator.)  
Set  Sets one or more fields in this object to the values specified in the given string, which should be a string in the Open Inventor file format.  
SetName  (Inherited from SoBase.)  
SetOverride  Turns the override flag on or off.  
SetSynchronizable  Sets this to be a ScaleViz synchronizable object.  
SetToDefaults  Sets all fields in this object to their default values.  
ToString 
Converts this SoBase structure to a human readable string.
(Inherited from SoBase.)  
Touch  Marks an instance as modified, simulating a change to it.  
Write  (Inherited from SoGroup.) 
Name  Description  

automatic 
Specifies whether to recompute the intersection automatically or not (default true).
If true, the intersection (curve or polygon depending on the #polygon field)
will be recomputed automatically when the scene or the plane changes. If false,
the intersection will only be recomputed when the recompute method is called.
 
plane 
Plane to intersect with.
Default is (1,0,0) at 0 (same as SoClipPlane).
Typically this field is connected from the clipping node's 'plane' field.
 
polygon 
Specifies whether to compute a capping polygon (default false).
If true, compute a capping polygon. If false, compute only the intersection curve.
 
scene 
Scene to intersect with plane. Default is none.
 
tolerance 
Tolerance for testing if vertices are equal.
Default is 1e6. This tolerance is used for calculation of triangle
intersections with the plane.

Name  Description  

boundingBoxCaching  (Inherited from SoSeparator.)  
boundingBoxIgnoring  Whether to ignore this node during bounding box traversal.  
fastEditing  Specifies the fast edit mode of the separator node.  
IsDisposable  ISafeDisposable interface implementation.
(Inherited from SoDisposable.)  
pickCulling  Whether to cull during picking traversal.  
renderCaching  Obsolete. Whether to cache during rendering traversal.  
renderCulling  Whether to cull during rendering traversal.  
renderUnitId  Used during the ScaleViz depth compositing process, this field specifies which render unit (OIRU) will render the sub scene graph below this separator.  
UserData 
Gets or sets the user data to be contained by the field container.
(Inherited from SoFieldContainer.) 
This class computes and (optionally) renders the intersection of the geometry in the specified scene graph with the specified plane. In curve mode it computes a set of line segments corresponding to the intersection. In polygon mode it computes a set of polygon boundaries that can be used as a "cap" for clipped geometry. The intent is that the specified scene graph is one shape. In fact it can be any scene graph, but the result is always a single polygon with multiple boundaries (if necessary). The computed vertices (and indices in polygon mode) can be accessed using the GetShape() method. The curve or polygon may be exported to a file like any other Open Inventor geometry using SoWriteAction, SoSTLWriteAction, etc.
Curve mode:
By default we compute and render the curve(s) defined by the intersection of the scene geometry and the plane. This is fast and works reliably for any Open Inventor geometry that produces triangles when an SoCallbackAction is applied (almost all Open Inventor geometry nodes). The appearance of the intersection curve can be controlled like any Open Inventor geometry using SoMaterial, SoDrawStyle, etc. nodes. The application may need to use an SoPolygonOffset node to "push" the scene geometry behind the intersection curve (polygon offset does not affect the intersection curve because it is a line set). Curve mode is useful to see where a clip plane intersects the geometry. Because it is much faster than polygon mode it is useful as a preview of where the polygons will be generated (if possible).
Polygon mode:
When the polygon field is set to true, the node converts the intersection curves to polygon boundaries. All the boundaries are stored in an SoIndexedFaceSet node and an SoShapeHints node is created with the 'windingType' field set to ODD_TYPE. All boundaries have counterclockwise vertex ordering and the face normal vector is the opposite of the current plane normal vector (because for a clip plane the plane normal points toward the unclipped half space which is effectively toward the interior of the shape). The appearance of the polygon can be controlled like any Open Inventor geometry using SoMaterial, etc. nodes. There are cases where polygons cannot be constructed, for example if the geometry is selfintersecting.
The coordinates of the intersection boundaries can be accessed using the GetShape() method. This is an SoLineSet in curve mode and an SoIndexedFaceSet in polygon mode. In either case the coordinates are in the shape's attached SoVertexProperty node. Note that in curve mode the line segments are in random order and do not form a connected polyline. This allows the intersection geometry to be computed in minimum time and does not (visually) effect rendering. If you need the boundary(s) as a connected polyline for some purpose, use the polygon mode. Note that in polygon mode there are redundant vertices in the vertex list because it still contains all the line segments. To follow the boundaries in connection order use the coordinate indices in the SoIndexedFaceSet node.
Notes:
Multiple boundaries in polygon mode.
Currently does not test if whether multiple boundaries are "holes" or "islands". Rendering should be correct in either case, but eventually some optimization could be done if all boundaries are disjoint.
Memory.
Memory allocated for vertices and indices is reused on each recomputation and is not freed until the node is destroyed. This is best for performance. Eventually there should be a method to force memory to be freed.
Limitations:
Valid geometry.
For polygon mode to work correctly, the geometry must obey the same rules as a valid STL geometry. In particular the geometry must form a closed solid and must not be selfintersecting. All the intersection boundaries must be closed and must not intersect any other boundary. However in curve mode, there are no limitations. For example, the node can be used to render the intersection of a surface with a plane.
Triangulation of the polygon.
This node simply computes the intersection boundary(s). For rendering it relies on Open Inventor to convert the polygon to triangles. In many cases the resulting triangles have a poor (large) aspect ratio.
Floating point precision.
Curve mode should work reasonably well with any geometry and any coordinates. However constructing polygon boundaries is very sensitive to floating point precision problems. If the results are not good, try adjusting the tolerance value.
Redundant coordinates.
In polygon mode the SoVertexProperty node contains all the coordinates computed for the intersection line segments. The SoIndexedFaceSet node only indexes a subset of these vertices (typically about half). Not removing the unused vertices saves time and has no effect on rendering. To get only the coordinates that are actually used, extract vertices based on the index values in the SoIndexedFaceSet node. Eventually could be an option.
Performamce.
This is currently a "brute force" implementation and performance could be better.
PlaneGeometryIntersection {
scene  NONE 
plane  1 0 0 0 
polygon  FALSE 
automatic  TRUE 
tolerance  1e6 