Circular Layout

Circular is a layouter that portraits interconnected ring and star topologies and is excellent for applications in:

– Social networking (criminology, economics, …)

– Network management

– WWW visualization

– eCommerce

Circular produces layouts that emphasize group and tree structures within a network. It creates node partitions by analyzing the connectivity structure of the network, and arranges the partitions as separate circles or disks. These circles are arranged in a radial tree layout fashion.

General Tab

Layout Style

Controls which policy is used to partition the nodes of the graph. Each node partition will be arranged as a separate circle or disk. Available options are

BCC Compact: Each partition will represent a so-called biconnected component of the graph. A biconnected component consists of nodes that are reachable by two edge disjoint paths. Nodes that belong to more than one biconnected component will be assigned exclusively to one partition.
BCC Isolated: Partitions will be formed as with BCC Compact with the difference that all nodes belonging to more than one biconnected component will be assigned an isolated partition.
Custom Groups: Partitions will be formed from groups created with Hierarchy->Group Selection.
Single Cycle: All nodes form a single partition.

Act on Selection Only

Whether or not to act on selected nodes and edges that are connected to selected nodes only.

Use Drawing as Sketch

Whether to use existing layout information. If enabled, the algorithm tries to:

– Find nodes that should lie on the border of the disks (for Disk or Organic Disk partition styles)

– Maintain the circular order of the border nodes around the center of the partition

– Keep the orientation of the root partition intact, if possible

– Maintain the cyclic order of tree edges around its parent node. For partition policies other than BCC Compact, this may not work as expected, since the underlying tree structure usually isn’t well defined

This option works best if the structural and layout changes are small, i.e. partition policy and partition layout style are kept.

Node Labeling

Specifies how to place node labels.

None: Automatic node labeling is deactivated.
Horizontal: All node labels are placed horizontally centered on the corresponding node. There will be no overlaps between node labels and other graph elements.
Ray-like: The algorithm places the label of nodes that belong to the perimeter of a circle ray-like outside the node with the same orientation as their nodes’ incoming edge.
Consider Position: The algorithm considers the current position of the node labels, i.e., the node labels keep their relative position and do not overlap with other graph elements.

Partition Tab

This section influences the layout style, size, and compactness of the partitions themselves.

Layout Style

Determine the basic layout style with which the partition contents are arranged.

Circle: This style places all partition nodes on the boundary of a single circle
Disk: This style only guarantees that nodes that have edges into other partitions lie on the border of a circle. All other nodes are placed in the inside of this circle and arranged with an organic layout style. The resulting arrangement usually is more compact than with the Circle style, at the price of a higher running time. This style is best suited when the focus lies primarily on the connections between different partitions, while also enhancing the structure of the partitions themselves.
Organic Disk: This style uses a different approach to create a compact arrangement. All nodes (even nodes with connections into different partitions) can be placed in the inside of a circle and are arranged with an organic layout style. The resulting arrangement usually is very compact and as organic as possible. However, connections to other partitions can be less obvious, so this style is best suited when the focus lies primarily on the structure of the partitions themselves, or for single cycle cycle partitions. Like Disk, this style is usually slower than the Circle style.
Compact Disk: This style creates a compact disk layout for each partition. Even nodes that connect to different partitions may be placed in the interior of the resulting disk.

Choose Radius Automatically

Whether or not to determine the radius of each circle in the layout automatically. An automatically chosen radius is usually the smallest possible radius that obeys Minimal Node Distance.

Fixed Radius

If Choose radius automatically is not set then this option determines the fixed radius for all circles in the resulting layout. Minimal Node Distance will be ignored in this case.

Minimal Node Distance

Determines the minimal distance between the borders of two adjacent nodes on a common circle. The smaller the distance the more compact the resulting layout. For the Disk layout style, this value is strictly observed only for nodes on the circle border, inner nodes may have a smaller distance. For the Organic Disk style, this value cannot be strictly guaranteed, but is observed as close as possible.

Node Types

Determines the type of the nodes. The nodes of a partition are sorted according to their type. In addition, the specified node types also influence the layout of the tree-like components.

None: The nodes have no types.
Defined by Color: The type is defined by the node color. Nodes with the same color have the same type.
Defined by Label: The type is defined by the node label. Nodes with the same label have the same type.

Edges Tab

This section contains settings with respect to edges including their routing style.

Interior Edge Style

Specifies the routing style for edges within partitions.

Straight: A routing style specifying that edges should be straight lines.
Curved: A routing style specifying that edges should be straight lines.

Inter Edge Style

Specifies the routing style for edges between partitions.

Straight: A routing style specifying that edges should be straight lines.
Curved: A routing style specifying that edges should be straight lines.

Circle Edge Style

Specifies the routing style for edges between neighbors in one partition.

Straight: A routing style specifying that edges between neighboring nodes should be straight lines.
Curved: A routing style specifying that edges between neighboring nodes of a partition are curved towards the circle’s center.
Curved on Circle: A routing style specifying that edges between neighboring nodes of a partition are curved outwards on the circle’s border.

Edge Routing Policy

Specifies the edge routing policy that determines whether edges are routed internally or externally with respect to a single partition circle.

Interior: An edge routing policy specifying that all edges are routed inside the circle and on its border as simple straight lines.
Automatic: An edge routing policy specifying that the algorithm automatically determines which edges to route internally and which externally.
Exterior: An edge routing policy specifying that all edges are routed around the exterior of the circle, except the ones that connect two neighboring nodes.
Selected Edges Exterior: An edge routing policy specifying that all selected edges are routed around the exterior of the circle and the remaining edges as simple straight lines.

Edge-to-Edge Distance

Specifies the minimum distance that exterior edges keep to each other.

Circle Distance

Specifies the minimum distance between the outer border of the circle partition and the arc path of exterior edges that run around the circle.

Preferred Angle

Specifies the preferred angle (in degrees) between adjacent segments of exterior edges at the same node. When the angle is zero, all exterior edges start/end with a segment of the same slope and, thus, overlap each other. The segment in this case is the extension of the line connecting the partition circle center with the respective node center.

Curve Length

Specifies the preferred length of the curve part that connects the first or last segment with the outer arc. An exterior edge consists of a straight part starting at the source node (or ending at the target node) and a main arc that runs around the exterior of the circle from source to target. A curve connects these two parts. Its length is configured by this setting.

Smoothness

Specifies the smoothness of the exterior edges which determines how many bend points are generated to approximate the curvature of the edge paths. The smoothness is defined to be a value between 0 and 1 where a higher value means smoother curves, and, thus, more bends.

Edge Bundling Tab

Enable Edge Bundling

Whether or not to enable the bundling of the edges. If enabled, the common parts of different edges are to some degree merged into a bundled part.

Bundling Strength

Determines how tightly the edges are merged/bundled if the Edge Bundling is enabled. The higher this value, the stronger the connection of the bundled edges.

Tree Tab

This section influences the compactness of the tree-like components that this layouter produces. The tree-like structures are the parts of the layout that do not belong to the circularly arranged node groups.

Preferred Child Wedge

This setting determines the angular range of the sector that will be reserved for the children of a root node. The possible angular range lies between 1 and 359. The remaining angular range (360-x) will be automatically used to accommodate the edge that connects to the root node.

The smaller the chosen value, the more one will gain the impression that the nodes drive away from their root nodes and the center of the graph.

Generally speaking, the compactness of the layout will decrease with smaller values. Very small values will lead to layouts that consume a lot of space.

Minimal Edge Length

Determines the minimal length of an edge that connects two nodes that lie on separate circles (tree-edges). The smaller the chosen value the more compact the resulting layout.

Maximal Deviation Angle

Whenever tree-edges connect to a node that lies on a circle together with other nodes, the layouter tries to direct that edge in such a way that its prolongation crosses through the center of the circle. This is not always possible though, for example, if multiple tree-edges connect to the same circle node.

This parameter determines the valid angular deviation from the optimal edge direction as described above. The bigger the chosen value, the more compact the resulting layout. If a value smaller than 90 degrees is chosen, the tree-edges might cross through the circularly arranged components.

Compactness Factor

This parameter influences the length of the tree-edges as it is computated by the layouter. The smaller the compactness factor, the shorter the tree-edges and the more compact the overall layout. The bigger the compactness factor the more difficult, and hence slower, the layout computation.

Minimal Node Distance

Determines the minimal distance between tree nodes.

Allow Overlaps

If activated this option further increases compactness of the resulting layout but may introduces slight node overlaps.

Place Children on Common Radius

Determines whether child nodes in a subtree structure have to be placed on a common circle. If this option is disabled, the resulting layout will be more compact.

Substructure Layout Tab

The algorithm can be configured such that it uses predefined layout styles for specific substructures contained in the input graph.

Stars

A star consists of a set of degree one nodes that are all connected to the same node (called the root of the star).

Ignore: The algorithm does not use a special layout style for stars.
Separated Radial: The set of degree one nodes associated with the same root are drawn as a separate structure in radial layout style. Compared to style “Radial”, this style does not place the nodes around the root node but in a separate structure connected to the root.
Radial: The set of degree one nodes associated with the same root are drawn in a radial layout style around the root node.

Separate Node Types

If enabled, nodes of different type are strictly separated during the substructure detection, see Node Types.

Arrows Define Edge Direction

If enabled, the arrowheads will be used to derive the direction of edges. An edge with an arrow at one end is considered to be directed. An edge without arrows or with arrows at both ends is considered to be undirected, which means that its direction is not important. The layout algorithm will use this information to determine the substructures, i.e., nodes may only be associated with the same substructure if this complies with the specified direction of the incident nodes. For example all edges of a chain or circle have to be directed in the same direction.

If this feature is disabled, all edges will be treated as undirected edges.

Hints

The most compact layout will be achieved by choosing
  Disk
or
  Organic Disk
as Partition Layout Style, small values for parameters
  [Partition]: Minimal Node Distance
  [Tree]: Minimal Edge Length
  [Tree]: Compactness Factor,
and big values for
  [Tree]: Preferred Child Wedge
  [Tree]: Maximal Deviation Angle.
If slight partition overlaps are acceptable, option
  [Tree]: Allow Overlaps
should be activated as well.