4 Component Navigation and Selection

An example component hierarchy is shown in Figure 15. At the top is a root model (class RootModel), in this case named Rigid Body Spring. The root model in turn contains a list of models, one of which is a mechanical model named msmod, which here contains particles and rigid bodies.

It is important to node that in the component hierarchy, any collection of components is itself a component (usually an instance of ComponentList). This provides automatic “grouping” of components of like type, but does introduce additional levels into the hierarchy. Hence the particle red is a child not of msmod, but rather the component list particles.

A navigation panel in the main ArtiSynth frame allows direct navigation of the component hierarchy. The panel can be open or closed by clicking on the main toolbar icon .

Figure 16 shows an navigation panel containing a superset of the hierarchy diagrammed in Figure 15.

Left clicking on any component in the navigation panel selects that component. Clicking while pressing the CTRL key (or the CMD key on some platforms, such as Mac) allows selection of multiple components. Clicking while pressing the SHIFT key allows selection of a range of components.

Components that are rendered in the viewer can generally be selected by variety of methods (the exception is for a few renderable components that do not support selection). These methods include click, box, and elliptic selection. The top two icons in the selection toolbar at the left of the ArtiSynth frame control the current selection method. In addition, hitting the ‘c’ key from within the viewer (Section 3.11) clears the current selection.

The selection display Figure 19 at the bottom of the main ArtiSynth frame shows the full path name of the last component added to the selection list. This is useful for identifying components in detail.

If no components are selected, then the selection display is blank.

The selection display is useful for disambiguating situations where it is not clear what component we have actually selected in the viewer. For example, FEM models keep their surface mesh contained within a descendant component. Selecting the surface mesh will cause this container component to be selected and highlighted, making it appear as though the FEM model itself is selected rather than the container. Checking the selection display makes it clear what component has actually been selected. If desired, one can easily navigate to one of the ancestor components using parent selection, as described in the next section.

Sometimes, when you select a component, you actually want to select one of it’s ancestor components.

There are several ways to do this:

1. 1.

   Hit the escape (ESC) key within the viewer window. This will select the parent of the currently selected component. Hitting escape repeatedly is a fast way to proceed up the component hierarchy.

2. 2.

   Click on the “up” arrow located at the left of the selection display (Figure 19). This will also select the parent of the currently selected component.

Parent selection is particularly useful in the commonly occurring situation where a composite component is not rendered and therefore not selectable in the viewer. For instance, suppose we wish to select a FEM model. One can select any renderable descendant of the model, such as a node, element, or its surface mesh (if displayed), and then use repeated parent selection until the model itself is selected.

Selected components are rendered in the viewer using a special selection color (yellow at the time of this writing). It is important to note that descendants of a selected component are not presently rendered in any special way. For instance, if an FEM is selected, it’s nodes and elements will be rendered normally.

While this has the potential to be confusing, we have not yet found this to be problematic, as the navigation panel and selection display provide alternative indicators as to what is currently selected.

A specialized tool is available for selecting FEM nodes, because it is often necessary to identify collections of nodes for connecting to rigid bodies or other FEM models, or to set localized properties and/or boundary conditions.

To open the node selection tool, first select the FEM model containing the nodes, and then invoke the context menu (usually via right-click) and choose “Select nodes ...”. A node selection tool will appear, as shown in Figure 20. From top to bottom, this contains several controls:

1. 1.

   A selection mode chooser that specifies how nodes are selected, possibly followed by mode-specific fields to adjust the selection behavior;

2. 2.

   An instruction box describing what action the user should take;

3. 3.

   A surfaceNodesOnly check box that allows selected nodes to be restricted to the FEM model’s surface;

4. 4.

   Buttons for clearing, growing or shrinking the selection, reducing the selection to its boundary, or for filling it in;

5. 5.

   Buttons for saving/loading a list of the selected nodes to/from a file, or for attaching or detaching selected nodes from other bodies.

While a node selection tool is open, GUI selections are restricted to certain components, usually nodes of the indicated FEM model. If surfaceNodesOnly is checked, selection is restricted to the FEM surface nodes. Selection is also held in a “multiple component” mode, equivalent to holding down the multiple selection key (usually CTRL), so that the selection can be easily edited and is not reset with each selection action.

The different selection modes and their parameters include:

INDIVIDUAL

Nodes are selected directly by the user, using click, box or elliptic selection (Sections 4.3.1 and 4.3.2). Selection is held in a “multiple component” mode, regardless of whether the “multiple selection” modifier key is pressed.

PATCH

Nodes are selected, on the mesh surface, within a patch region defined by a set of faces for which the bend angle between adjacent faces is less than or equal to a specified maximum bend angle. The bend angle is defined as the absolute value of the angle between two faces along their common edge, such that parallel faces have a bend angle of and perpendicular ones have a bend angle of . Within the tool, the maximum bend angle is specified (in degrees) by the field maxBendAngle. To find the patch nodes, the user selects a node within the desired patch area. Starting with the node’s adjacent faces, the patch is then grown outwards to find all neighboring faces such that the bend angle between them does not exceed maxBendAngle (Figure 21, left).

EDGE_LINE

Nodes are selected, on the mesh surface, along an edge line defined by faces meeting at a bend angle greater than or equal to a specified minimum bend angle. Within the tool, this minimum angle is specified (in degrees) by the field minBendAngle. To find edge line nodes, the user selects a node lying along the desired edge line. The line is then followed from node to node, by locating edges with a large enough bend angle.

EDGE_LINE selection is illustrated in Figure 22, and the following fields adjust its behavior:

minBendAngle

Minimum bend angle, described above.

maxEdgeAngle

Specifies (in degrees) the maximum edge angle between two adjacent edges along the edge line. Line following is terminated when the angle between the current edge and the next edge exceeds this threshold.

allowBranching

If selected, allows the edge line to branch in different directions. Otherwise, edges are followed sequentially so as to minimize the edge angle between them.

DISTANCE

Nodes are selected based on being within a prescribed distance of a polygonal mesh, which may be the surface mesh for a rigid body or FEM model, or some other mesh component. The distance threshold is specified by the field distance. To select nodes, the user may select any mesh component containing a polygonal mesh. The user may also select a rigid body or FEM model, which will cause the body’s surface mesh to be used for the distance calculation.

The following fields adjust the behavior of DISTANCE selection:

distance

Distance threshold, described above.

useSignedDistance

If selected, causes the distance computation for closed meshes to be signed, so that nodes inside the mesh will have a negative distance. This means that for a non-negative distance threshold, nodes inside the mesh will always be selected.

surfaceNodesOnly

If checked, the selection is restricted to the FEM model’s surface.

MINIMUM_PATH

In this mode, the user selects an individual node, and the tool then selects a minimum path of nodes between it and the previously selected node. This is particularly useful for “drawing” the boundary of a nodal region on the FEM model’s surface.

If surfaceNodesOnly is checked, the path will be restricted to the FEM surface; otherwise, the path may proceed through the FEM interior.

When forming the path, the tool chooses from adjacent nodes based on the topology induced by the FEM elements. This can sometimes lead to a path that is less minimal than if nodes could be chosen arbitrarily, particularly for quadratic hex, wedge and pyramid elements.

The user is free to change modes during the selection process. Because selection is held in multiple selection mode, it is easy to edit the selection. In particular, INDIVIDUAL selection can be used for fine editing of selections obtained using PATCH, EDGE_LINE, DISTANCE, or MINIMAL_PATH.

Below the surfaceNodesOnly check box, the tool contains a number of buttons:

Clear

Unselects all the nodes.

Grow

Enlarges the current selection to include adjacent nodes.

Shrink

Reduces the current selection by removing nodes on the boundary.

Boundary

Reduces the current selection to include only its boundary nodes (Figure 21, right).

Fill

Fills a region in the current selection. After clicking this button, the user selects a node inside the desired region. The selection is then grown outward from the selected node until it reaches the region’s boundary.

Attach nodes

Attaches the selected nodes to another body which is either a rigid body or an FEM model. The body may be chosen by selecting it directly, or by selecting one of its component meshes. Nodes which are currently attached are not attached to the body.

Detach nodes

Detaches all selected nodes from any body or particle that they are currently attached to.

Save

Saves the nodes to a file that has been previously specified using either “Save as ...” or “Load ...”.

Save as ...

Saves the nodes to a user-specified text file. The format consists simply of integer node numbers (with respect to the selection tool’s FEM model), separated by white space. More details on the file format are given in the section “Selecting nodes in the viewer” of the ArtiSynth Modeling Guide.

Load ...

Loads the selected nodes from a text file, the format for which is described under “Save as ...”.