Next, we turn to tools that allow you to construct spatial networks, add or remove Origins and Destinations on the networks and delete networks.
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Any network analysis in the Rhino UNA toolbox requires at least two geometry inputs—first, an input analysis network along which all trips are computed, and second, Origin and Destination points, where movement starts or ends.
The Add Curves to Network tool prompts you to select curves that you want to build your network out of. Select all the curves you want to involve in the network and press enter. This will automatically turn the selected curves into a network and build an adjacency matrix that is used for analysis.
Add/Remove Curves tool
The Add Curves to Network tool offers several options on the command line:
Options ( Weight=Length DefaultValue=0.01 FallbackType=Length ):
Weight = Length option is the default weight that is applied to determine the network cost for each segment. The default option is Length, using distance units in the given Rhino file (e.g. if the Rhino file is in meters, Length cost here will be in meters).
The default Weight can be changed to an alternative attribute by the user to add custom costs for calculating lowest cost routes to destinations. This allows routing algorithms to account for different perceived qualities of network segments for pedestrians. For instance, a street with wider sidewalks, more ground floor amenities or more tree cover may be perceived as preferable by pedestrians, therefore having a lower perceived cost than another street of the same length without such attributes. If segments with desirable qualities are assigned a correspondingly lower Weight, then they will likely attract more journeys to them since a number of different UNA tools work with cost minimization.
Custom costs can be applied to the network to account for specific conditions such as route quality which may reduce perceived route length and thus alternative route choices. The route on the left may represent the shortest distance path, but conditions may be less attractive for pedestrians. The route on the right applies a 0.5 multiplier to a street where pedestrian conditions are more attractive. Origins in blue. Destinations in red.
For practical purposes, when you work with custom network segment Weights, we suggest that you think of them in “distance equivalent” units–this allows you to use the same cost units (e.g. Length in meters, feet etc.) as in your drawing file. This means you can synthesize how the various qualities of network segments affect their perceived cost and change the segment Weight to Perceived Length ensuring that more desirable segments have lower perceived lengths and less desirable segments higher perceived lengths than their raw geometric length.
Literature on pedestrian path choice can provide some guidance in understanding how various street attributes can affect their perceived length for pedestrians. Basu and Sevtsuk (2022), synthesizes findings from a number of different pedestrian path studies to distance-equivalent terms and can be used as a resource for setting a custom Weight for segments.
Note that not all segments require a value for this option. The Fallback Type (described below) tells the tool what other cost units to use when no custom weight is available on some segments. See Add Numeric Attribute on how to assign weights.
DefaultValue = 0.01 is the default value for non-numerical or error values within the selected Weight attribute.
Fallback Type = Length is the default attribute value that will be used for segments that lack the selected attribute Weight. Using Length as the default Fallback Type for segment costs further highlights why it is useful to work with “perceived lengths” as custom costs—if you do not have detailed data on the qualities of all network segments but only some, you can just assign a custom Weight to select segments and rely on the raw Length on all others–the two costs are compatible with each other. This way, you do not necessarily have to populate the whole network with custom attribute costs.
In order to use newly added custom network segment weights in UNA analyses, you need to rebuild the network with the Add/Remove Curves from Network tool–adding custom Weights to an existing network will not be available to analyses tools until the network has been rebuilt.
Through a left click, the tool also enables you to add curves to an existing network. If some of the curves you might be adding to a pre-existing network are already part of the network, their GUIDs will be recognized and they will not be double represented. Right-clicking the tool, on the other hand, allows you to remove curves from an existing network.
In order for network analyses to work, network curves need to provide continuity between the Origin and Destination points you analyze (see figures to the right). If your network curves do not share a common end node, then Origin and Destination points found on different network segments might not be topologically connected to each other. If one curve ends on top of another, but the latter does not have a node at the intersection (e.g. T intersection with no shared endpoints), then there is no topological continuity between the two curves. Curves that intersect without sharing a common node can be used to model three-dimensional overpasses or underpasses.
The tool can accept any kinds of curves to participate in networks — lines, polylines, curves, arcs, etc. Networks of these curves can either be planar (2D) or three-dimensional, as long as adjacent curves share a common end node with each other. While 2D networks may be adequate for representing street and building networks in urban settings, 3D networks offer additional opportunities for analyzing circulation systems and layouts within buildings or in multi-layered urban infrastructure systems.
For visual clarity, the default settings in the UNA Graphic Options will visualize dead-ends or “naked edges” of the network with little black crosses (Figure 28). You can turn these black crosses off in the Graphic Options by turning off Nodes. The black crosses can be useful to visualize where your network might contain topological errors. In Figure 28, for instance, the first intersection from the top has topology issues. A black cross is drawn, indicating that one or more curves around that node has a dead end and does not connect to any other curve. On the second node, a red warning with a numeric value “2” is displayed. This warning, which can also be toggled on or off in the Graphics Options using the NodeD2 setting, detects “degree 2” nodes — that is nodes that have exactly two curves intersecting at the node. In this case it signals two polylines meeting at right angles, instead of four segments sharing an endpoint.
No nodes at intersection: no continuity between 2 curves
1 node at intersection: no continuity between 2 curves
3 nodes at intersection: continuity between all 3 curves
The Add Origins tool adds trip Origin locations to the network. As with network lines, left-clicking adds Origin points, right-clicking removes Origin points.
All UNA analysis functions require both Origin and Destination points, which can designate any spatial locations, such as address points, buildings, entrances, rooms in a building or even locations in utility or infrastructure networks, such as airports, stations etc. Analysis results are typically computed for either Origin or Destination points (and sometimes observer points), depending on the UNA tool used. For instance, Accessibility results, such as Reach or Gravity metrics, are always returned for Origin points, while Closest Facility results are instead returned to Destination points.
The tool first asks for a selection of points. After selecting points graphically (or right-clicking on a layer > Select Objects), the following options appear on the command line:
Press Enter to add origins to network
(Search=2D SavedEdges=On):
Search = 2D option determines whether the added points are snapped to the network in two-dimensional (default) or three-dimensional space. For planar networks, where all network links are on the same level (as is the case with many urban street network datasets), it is advisable to use 2D search, which functions faster than 3D search. When three-dimensional networks, such as building circulation networks, or multi-level urban networks are used, the Search option should also be set to 3D.
SavedEdges = On option allows you to check if a point has a saved edge that it is designated to. It is possible to tie a point to a particular edge of the network, which may not necessarily be the closest edge, using the unaBindEdge function from the command line. If the edge reference that a point carries is not found in the drawing file, regular closest edge joining is used. You can typically ignore this input.
Once you have added Origin points, each point is associated with its closest network element with a blue connection line. The location at which this blue connection line snaps to the original network, designates the assumed network location of the point. You can toggle the blue connection lines on or off in the Graphic Options by changing the DotConnections = On option.
Add/Remove Origins tool
Origin points are tied to the network with blue dot connections
The Add Destinations tool adds trip Destinations to the network. Left-clicking the tool adds Destinations points to the network, right-clicking removes Destinations points from the network.
The tool first asks for a selection of points. After selecting points graphically (or right-clicking on a layer > Select Objects), the following options appear on the command line:
Search = 2D option determines whether the added points are snapped to the network in two-dimensional (default) or three-dimensional space. For planar networks, where all network links are on the same level (as is the case with many urban street network datasets), it is advisable to use 2D search, which functions faster than 3D search. When three-dimensional networks, such as building circulation networks, or multi-level urban networks are used, the Search option should also be set to 3D.
SavedEdges = On option allows you to check if a point has a saved edge that it is designated to. It is possible to tie a point to a particular edge of the network, which may not necessarily be the closest edge, using the unaBindEdge function from the command line. If the edge reference that a point carries is not found in the drawing file, regular closest edge joining is used. You can typically ignore this input.
Once you have added Destination points, each point is associated with its closest network element with a red connection line. The location at which this red connection line snaps to the original network, designates the assumed network location of the point. You can toggle the red and blue connection lines on or off in the Graphic Options by changing the DotConnections = On option.
Add/Remove Destinations tool
Destination points are tied to the network with red dot connections
Observer points are only used in Betweenness analysis. They enable you to return Betweenness results for points that are neither Origins nor Destinations themselves, but rather locations that are potentially passed by trips between other Origins and Destinations. If trips originate from bus stops and go to shops, for instance, then building points in between bus stops and shops can be used as Observers to illustrate how many trips pass by each building. Betweenness analysis keeps track of how many times each Observer point is passed in the analysis. The weights of Observer points are not used as part of any analysis. Observer points are tied to the network with gray dot connections, which indicate their network locations. Just like adding Origins or Destinations, left-clicking the tool adds Observers, right-clicking removes Observers from the network.
Note that Observer points can be particularly relevant if the Origin and Destination points are located on the same edge segment. Betweenness results for observer points are always exact, while the Betweenness values for edges are approximations, found by taking the average of Betweenness values of the segment’s end nodes. Edge values can thus under-represent trips, where Origins and Destinations lie on the same network segment.
Add/Remove Observers tool
Observer points are tied to the network with grey dot connections
Search = 2D option determines whether the added points are snapped to the network in two-dimensional (default) or three-dimensional space. For planar networks, where all network links are on the same level (as is the case with many urban street network datasets), it is advisable to use 2D search, which functions faster than 3D search. When three-dimensional networks, such as building circulation networks, or multi-level urban networks are used, the Search option should also be set to 3D.