Glossing & Retracing of Existing Routes on a PCB in Altium NEXUS

Created: May 16, 2022 | Updated: June 30, 2022 | Applies to version: 5

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Parent page: Routing the PCB

Routing a printed circuit board is a detailed, iterative process. Rarely are you able to simply route, or ActiveRoute, all of the nets in a single pass. More often you will be routing a set of nets and as you move on to the next set of nets, you are continually adjusting and moving existing routes, perhaps manually dragging them, or perhaps pushing and shoving them as you interactively route more nets.

The end result is that your finished routing can end up looking like it was autorouted, with lots of unnecessary jigs and corners.

Re-routing & Rearranging Existing Routes

Routing a board can be a complex and time-consuming process as you work to position the components and complete the routing - move that component slightly, shove that routing, re-route those critical nets to avoid potential cross-talk, now see if that bus can be routed through that area, and so on. As you route your board, you will be constantly modifying routing that you have already done.

There are two approaches to modifying the routing; you can either reroute or re-arrange.

Rerouting is ideal when the new route path is more complex than simply moving a few track segments. Rerouting is performed in the same way as the initial routing using the Interactive Routing (or Interactive Differential Pair Routing) command - when you complete the new route path the old loop of redundant track segments is removed.

Alternatively, you can re-arrange the routing. To re-arrange existing routing, click and hold on a track segment then drag it to its new location. Connected track segments will remain connected at the angle they were previously connected - a behavior called interactive sliding. Interactive sliding also supports the Conflict Resolution Modes, including Push, Hug and Push, and Ignore.

Move - to move an object without regard to other objects that connect to it.

Drag - to move an object and have any connected objects remain connected to it. The connected objects may or may not retain their original placement angle.

Slide - to move a routing object and have the connected objects remain connected, with those objects retaining their original placement angle.

As well as using one of the Route » Un-Route commands to remove existing routing, it can often be quicker to select the track segments and delete them. Check out the Strategies for Selecting the Routing page for tips and techniques on selecting routing.

Reroute an Existing Route

There is no need to un-route a connection to redefine its path; simply click the Interactive Routing button on the Active Bar () and start routing the new path.
The Loop Removal feature will automatically remove any redundant track segments (and vias) as soon as you close the loop and right-click to indicate you are done.
You can start and end the new route path at any point, swapping layers as required.
You can also create temporary violations by switching to Ignore Obstacle mode (as shown in the video below), which you later resolve.

A simple animation showing the Loop Removal feature being used to modify existing routing.

Rearrange Existing Routes

To interactively slide or drag track segments across the board, click, hold and drag as shown in the video below.
The default dragging behavior is configured on the PCB Editor - Interactive Routing page of the Preferences dialog.
The PCB editor will automatically maintain the 45/90 degree angles with connected segments, shortening and lengthening them as required.

A demonstration of interactive sliding being used to modify the existing routing.

Interactive Sliding Tips

While sliding a route you can move the cursor and hotspot snap it to an existing, non-moving object such as a pad. Use this to help align the new segment location with an existing object and avoid very small segments being added.
During sliding, one of the Routing Conflict Resolution modes applies. Press Shift+R to cycle through the modes as you drag a track segment.
To convert a 90-degree corner to a 45-degree route, start dragging on the corner vertex.
The interactive sliding engine includes algorithms specifically for dragging a vertex (corner), configure the Vertex Action in the Preferences dialog, or in the Interactive Sliding mode of the Properties panel. Press the Spacebar to cycle through the modes as you drag a vertex.
To break a single segment, select the segment first, then position the cursor over the center vertex to add in new segments.
Existing pads and vias will be jumped, or vias will be pushed if necessary and possible when the Allow Via Pushing option is enabled.
Interactive sliding supports non-orthogonal routing.
The default behavior is to drag (slide) tracks (selected or unselected). If you need to move a segment without maintaining its connection to the attached segments, change the default dragging behavior using either the Unselected via/track or the Selected via/track options on the PCB Editor - Interactive Routing page of the Preferences dialog.

Modifying T-Junctions

There is specific support for interactively modifying a T-junction - click and drag on the junction point to modify a T-junction.

Examples of the T-Junction dragging capabilities.

Interactive Via Dragging

PCB designers can spend a lot of time adjusting the routing, perhaps due to a late design change, or to achieve completion of their design. This can mean pushing and shoving existing routing, dragging vias, and nudging components.

Adjust the via dragging behavior in the Properties panel.

Complimenting the support for glossing of neighbor routes, via dragging is also supported. Via dragging supports Neighbor Glossing, configured through the Interactive Via Dragging mode of the PCB editor's Properties panel. Press Tab during via dragging to access the panel and adjust the settings.

Press Tab as you drag to configure the Via Dragging options.

Differential Pair Dragging

To recognize the members in a differential pair, the concept of Coupling is used. When the software recognizes objects that belong to a differential pair it will attempt to drag the pair's partner track or via if the Keep Coupled option is enabled in the Interactive Sliding or the Interactive Via Dragging modes of the Properties panel.

Press X as you drag a via-pair to rotate the pair by 90 degrees.

To confirm that the partner objects are coupled, the software checks that the objects:

For via pairs - belong to the pair, and are closer than 2 * Preferred Gap
For track pairs - belong to the pair, are on the same layer, are separated by no more than the Preferred Gap

Options that Affect Routing, Rerouting and Interactive Sliding

There are a number of options that impact the rerouting behavior, these options are configured in the PCB Editor - Interactive Routing page of the Preferences dialog.

The Automatically Remove Loops option must be enabled to perform rerouting. There are situations when you may want to create loops, for example, power net routing. If necessary, Loop Removal can be disabled for an individual net by editing that net in the PCB panel. To access the option, set the panel to Nets mode, then double-click on the net name in the panel to open the Edit Net dialog.
As with Interactive Routing, the Current Routing Conflict Resolution mode will be used.
- Use the checkboxes to enable only those modes you want to be available in the Current Mode list.
- Press Shift+R to cycle through the enabled modes as you reroute.
The Automatically Terminate Routing option is useful. If it is enabled, as soon the new route connects to the existing routing, the redundant loop is removed (as shown in the video above). If this option is disabled, the loop is removed when you right-click to release the current route. The option can work against you when you need to place new routing on top of the existing routing (perhaps overlapping), in this situation it can be better to disable it.
The Glossing Effort options control how strongly the routing engine attempts to smooth or gloss the routing being modified, and it does this based on the Hugging Style, Arc Ratio, Miter Ratio, and Pad Entry Stability settings. Learn more about glossing in the, Improving the Quality of the Routing section below.

Interactive Routing and Interactive Sliding Panels

Whether you're interactively routing a connection or dragging an existing route to make way for more routing, the same set of routing technologies are applied. This section summarizes the options available in the Interactive Routing and the Interactive Sliding modes of the Properties panel. Press Tab as you work to open the Properties panel in the relevant mode. After changing the settings, click the icon in the middle of the screen to return to routing or sliding. The default settings for these options are configured in the PCB Editor - Interactive Routing page of the Preferences dialog.

Interactive Routing and Interactive Sliding Options

Routing Gloss Effort (Routed)

During a route event, such as interactive routing, interactive sliding, or ActiveRouting, the software runs the glossing engine. The glossing engine constantly reviews all of the segments placed or impacted by the current route event, attempting to improve the quality of the results. Measures of quality include: reducing the number of corners, reducing the number of segments, removing acute angles and reducing the overall route length.

Glossing has three settings:

Off - in this mode, glossing is essentially disabled. Note, however, that cleanup is still run after routing/dragging occurs to eliminate, for example, overlapping track segments. This mode is typically useful at the end stage of board layout when the ultimate level of fine-tuning is required (for example, when manually dragging tracks, cleaning pad entries, etc.).
Weak - in this mode, a low level of glossing is applied, with the Interactive Router considering only those tracks directly connected to or in the area of the tracks that you are currently routing (or tracks/vias being dragged). This mode of glossing is typically useful for fine-tuning track layout or when dealing with critical routes.
Strong - in this mode, a high level of glossing is applied with the Interactive Router looking for shortest paths, smoothing out tracks, etc. This mode of glossing is typically useful in the early stages of the layout process when the aim is to get a good amount of the board routed quickly. Note that when Strong glossing is combined with one of the arc in corner modes, it also allows any-angle traces. The assumption here is that since the designer is curving the corners they will be comfortable with non-orthogonal routing between corners.

Routing Gloss Effort (Neighbor)

Gloss Effort (Neighbor) configures the amount of glossing applied to adjacent routes that are impacted by the current interactive routing or sliding. It also has three settings; Off, Weak and Strong.

Hugging Style

This option controls how corner shapes are to be managed during interactive sliding and will affect both the tracks being slid and the tracks being pushed. During sliding use the Shift+Spacebar shortcut to cycle through the three modes.

45 Degree - always use straight orthogonal/diagonal segments to create corners during sliding (use this mode for traditional orthogonal/diagonal routing behavior).
Mixed - use straight track segments when the objects being moved/pushed against are straight, use arcs when they are curved.
Rounded - use arcs at each vertex involved in the move/push. Use this mode for snake routing, and to use arcs + any angle routes when glossing (during interactive routing and manual glossing).

Routing Mode / Sliding Mode

This option determines how you want the routing/sliding objects to react when they encounter an existing object. Use the Shift+R shortcut to cycle through the available modes during sliding.

These are the modes that are referred to as the Routing Conflict Resolution modes in the PCB Editor - Interactive Routing page of the Preferences dialog.

Vertex Action

To better support the designer's need to easily manipulate and re-shape the existing routing, there are specific options that are applied when you click and drag on a vertex rather than a track or arc (the vertex is the corner location where two segments meet). Use the Spacebar shortcut to cycle through the available modes during sliding.

Deform - break or lengthen the track segments attached to the moving vertex so that the vertex follows the cursor movement.
Scale - hold the corner shape and resize and move the incoming track segments, keeping the vertex attached to the cursor.
Smooth - reshape the corner smoothly, inserting arcs to create a curved corner when dragging inward (in Mixed or Rounded Hugging Style), at every vertex impacted by the sliding process. Also, add arcs when dragging outward in Rounded Hugging Style.

Checkbox Options

Automatically Terminate Routing - when the current connection being routed reaches the target pad, automatically stop routing that net but remain in the Interactive Routing command, ready to start routing another net.
Automatically Remove Loops - when this option is enabled you can route a new path for an existing route - when the new route path comes back to meet the existing path the redundant loop is automatically removed.
Remove Net Antennas - a net antenna is a short, unterminated track (arc) segment. These are automatically removed if the current routing impacts an object that the antenna is touching.
Allow Via Pushing - during routing/sliding in Push or Hug & Push modes, allow existing vias to also be pushed.
Display Clearance Boundaries - display the no-go area around existing objects, defined by the applicable Clearance design rule(s).
- Reduce Clearance Display Area - reduce this display to a circular zone around the current cursor location.
Show Length Gauge - the length gauge indicates how well the current route is meeting applicable Length and Matched Length design rules. Learn more about Length Tuning.

Pad Entry Stability

The Pad Entry Stability slider protects centered pad entries, preventing Glossing from un-centering a centered track (it holds a centered track on-center, it does not center an un-centered track). Use the slider bar to configure the level of protection:

Off = no protection
Max = maximum protection

Miter Ratio

The Miter Ratio controls the minimum corner tightness. The Miter Ratio multiplied by the current track width equals the separation between walls of the tightest U-shape that can be routed for that ratio, as shown in the Mitered Corners description, earlier on this page. Enter a positive value equal to or greater than zero (the x multiplier is added automatically).

Min Arc Ratio

The Min Arc Ratio is applied during any angle interactive routing and also during interactive sliding with Mixed Hugging Style. The ratio is used to determine the minimum radius arc allowed, when the arc radius falls below this minimum the arc is replaced by track segments, where:

Min Arc Radius = Min Arc Ratio x Arc Width

This setting is not applied during any arc in corner routing or interactive sliding with Rounded Hugging Style, as these modes do not use segmented arcs.
Set the Minimum Arc Ratio to 0 (zero) to always use arcs.

Routing-Aware Move Component

While routing the board, it is not uncommon for the designer to need to adjust the location of a routed component to create space for new routing. To help with this, the PCB editor includes a routing-aware move component feature. The feature is enabled via the Component Re-route checkbox, in the PCB Editor - Interactive Routing page of the Preferences dialog. Essentially, the feature will break the routing at the component pads, fanouts or escape routes, and then attempt to re-route those broken connections once the moving component(s) has been placed.

A key requirement of the feature is to preserve fanouts and escape routing. To support this, the Shift+Tab shortcut is used to cycle through the possible sets of objects being moved, as detailed below.

During the move process, the options can be controlled using the following shortcuts:

Component Re-route Mode (Shift+R) - toggles the re-route mode on and off. After the moving set has been released, the software will attempt to re-route the component(s) to reconnect any broken nets. Use the Shift+R shortcut to disable the Component re-route option in Interactive Routing page of the Preferences dialog. The current Component Re-route status is displayed in the Heads Up display and on the Status bar.
Change Component Selection (Shift+Tab) - while dragging, the set of objects being moved can still be changed. Press Shift+Tab to cycle through the following selection sets:
- Components only, then
- Components +Via Fanouts +Escapes +Interconnects, then
- Initial selection set (if different from the previous two), then
- Back to Components only.
The Move component with relevant routing option behaves as follows:
- Enable the option to start the move component action with the relevant routing (Components +Via Fanouts +Escapes +Interconnects), use the Shift+Tab shortcut to cycle the selection set as described above.
- Disable the option to start the move component action with components only selected. Because the set of relevant routing objects is detected prior to the move commencing, it is not possible to use Shift+Tab to cycle through the selection set when the option is disabled.

When the Component Re-route option is enabled, connected routes are restored after the moving component is placed.

For better control of how pads of the component being moved should be connected with the objects of the same nets, you can use the N key to cycle through net line connect modes. The following modes are supported:

Pad to Pad - during the move, connection lines displayed between pads of the component being moved and the nearest pads of the same nets on the board.
Breaks - during the move, connection lines displayed between pads of the component being moved and the track breaks of the same nets on the board.
Hidden - connection lines hidden.

Current net line connect mode is shown in the Heads Up Display (HUD) when a component is moved.

Improving the Routing

To help produce neat routing with the minimum number of corners, the PCB editor also includes a Glossing tool. Glossing is a sophisticated set of algorithms developed specifically to produce cleaner routing and pad entries, that respect the intent of the applicable design rules. Glossing attempts to reduce the path length and also improve the shape of corners and reduce their number, generally resulting in neater routing created from fewer segments. Glossing also leaves sub-net jumpers as they were, and when there are room-based width rules, width changes at the boundary are respected. As you move the cursor around as you define a new interactive route path, all of the yet-to-be committed routing is also automatically glossed.

The Glossing engine also includes a Retrace Selected command. Use this when you need to update selected routes to the changes you have made to settings in the routing rules. With Retrace you can "fatten up" that existing power routing, or update that differential pair to new width and gap settings.

Glossing focuses on improving the trace geometry, where Retrace assumes the overall geometry is satisfactory, focusing instead on satisfying the design rules.
Glossing preserves the existing trace width and differential pair gap, while Retrace changes them to Preferred.
Glossing runs whenever ActiveRoute finishes, if the Gloss Results option is enabled in the PCB ActiveRoute panel.
Glossing also runs during interactive routing, on all track segments that are yet to be committed (all segments placed since the Interactive Routing command was launched and you started routing a net).

Glossing - Improving the Quality of the Routing

The PCB editor includes powerful tools for improving the quality of existing routing. Whenever you move the cursor to define a new route path, all of the proposed routing is automatically glossed. Glossing will attempt to reduce the path length, and also improve the shape of corners and reduce their number, generally resulting in neater routing created from fewer segments.

Glossing has three settings; Off, Weak and Strong. Use the Ctrl+Shift+G shortcut to cycle through the settings during interactive routing or interactive sliding, or press Tab to open the Properties panel and select the setting. Along with the current Gloss Effort settings, Glossing also obeys these settings:

Corner Style
Hugging Style (during Interactive Sliding and also when the Gloss Selected or Retrace Selected commands are run)
Miter Ratio
Min Arc Ratio

Using these options, Glossing controls how tightly a corner is created and how the curved shape is formed in the route around a curved obstacle.

Existing routing can be glossed by running the Route » Gloss Selected command. Use this to your advantage to perform design changes, such as converting mitered corners to arcs, by configuring the Corner Style before running the command.

Existing routing can also be retraced (Route » Retrace Selected). Retrace assumes the overall geometry is satisfactory, focusing instead on verifying that the routing meets the design rules. Where Gloss preserves the existing trace width and pair gap, Retrace changes them to Preferred. Retrace is an excellent tool to use when a design rule has changed, and that change needs to be applied to existing routing.

The Gloss Effort (Routed) option controls how strongly the routing-under-edit is glossed, and the Gloss Effort (Neighbor) option controls how strongly the routing that is being pushed is glossed.

► Build your Interactive Routing proficiency

As well as selecting the routing to be glossed, there are also a number of options that control glossing behavior.

Glossing runs during Interactive Routing or when ActiveRoute completes (if the Gloss Results option is enabled) obeying the current settings configured in the PCB Editor - Interactive Routing page of the Preferences dialog. See the Options that Control Glossing Behavior during Interactive Routing section to learn more.
A manually-run glossing pass on the selected routing obeying the current settings configured in the PCB Editor - Gloss And Retrace of the Preferences dialog or in the Gloss And Retrace panel. See the Options that Control Glossing and Retracing Behavior on Selected Routing section to learn more.

Summary of Glossing Behavior

To summarize:

Flexible approaches to selection can be used, supporting partial glossing of a routed net:
- To gloss only a section of a routed net you can select a track segment at either end of the section or select a pin or a via to signify the end of the desired section.
Glossing attempts to repair dangerous pad entries:
- Gloss does not automatically comply with the SMT rules (SMD Entry & SMD To Corner) if it detects that they are encouraging unnecessary jogs and circuitous routing.
- If SMT rules rules are present the gloss engine tries to recognize dangerous situations, such as the potential for solder bridging, and adjusts its behavior based on these rules.
- For this to occur, the Corner option must be disabled in the SMD Entry rule, and the SMD To Corner rule must have a suitable setting.
- Rule deviations: Gloss will keep the track segment orthogonal with the pad edge being exited from, but will not necessarily keep it centered within that edge. Gloss will also allow the track segment to exit from the side of the pad if the SMD to Corner distance and other applicable rules can be satisfied.
Glossing differential pairs:
- When applied to differential pair routes, Gloss attempts to zip-up the pair, reducing the lengths of the unzipped portions. The corresponding unzipped portions from opposite sides are made equal in length, if possible, but Gloss does NOT add meanders to the shorter side of the pair. If length balancing is not achieved naturally, the pair is left unbalanced.
- Particular attention is applied to differential pair pad entries to improve their quality, but Gloss does not attempt to match the lengths of the entry routes.
- Where differential pair routes cross a room boundary and change width, Gloss gives preference to synchronous width change of the pair members. This means it does not change the width/gap of both routes right on the boundary, instead it focuses on keeping the pair matched, so when a width change occurs, it happens to both segments at the same time. So if the routing enters the room at an angle, one route in the pair will change width on the room boundary, and the second route in the pair will change width at a location adjacent to the first route. (show image)
Support for Subnet Jumpers:
- Gloss treats Subnet Jumper tracks as fixed.
Support for room-based rules:
- Gloss adheres to Clearance and Diff Pair Routing rules scoped to rooms.
- Gloss allows the route to change width as it enters a room; it will attempt to preserve the original widths used both outside and within the room.
- If there is a width change at a room boundary, Gloss will maintain the width change.
Exclusions:
- To exclude routes from glossing or retracing, lock the track segments.
- Tracks at non-45 degree angle increments are not glossed; it is assumed these have been placed intentionally to satisfy a design requirement.
Feedback:
- Command and progress information is displayed on the Status bar.
- Info and Warning messages are displayed in the Messages panel. Details are in the Information and Warnings section below.

If a Route Guide has been used, the routes within the guide are not glossed because glossing is not aware of the route guide shape.

Options that Control Glossing Behavior during Interactive Routing

Gloss Effort (Routed)

How strongly a route is glossed is controlled by the current Gloss Effort (Routed) setting. Configure the option in the Interactive Routing page of the Preferences dialog, or use the Ctrl+Shift+G shortcuts to cycle through the three modes. The current setting is displayed on the Status bar. (show image)

Off - In this mode, glossing is essentially disabled. Note, however, that cleanup is still run after routing/dragging occurs to eliminate, for example, overlapping track segments. This mode is typically useful at the end stage of board layout when the ultimate level of fine-tuning is required (for example, when manually dragging tracks, cleaning pad entries, etc.).
Weak - In this mode, a low level of glossing is applied with the Interactive Router considering only those tracks directly connected to or in the area of the tracks that you are currently routing (or tracks/vias being dragged). This mode of glossing is typically useful for fine-tuning track layout or when dealing with critical traces.
Strong - In this mode, a high level of glossing is applied, with a strong emphasis on the shortest path. This mode of glossing is typically useful in the early stages of the layout process when the aim is to get a large portion of the board routed quickly.

Gloss Effort (Neighbor)

Gloss Effort (Neighbor) configures the amount of glossing applied to adjacent routes that are impacted by the current interactive routing or sliding. It also has three settings; Off, Weak and Strong.