Carlson RoadNET: Adding and Editing Intersections

Carlson RoadNET: Adding and Editing Intersections

Intersections are created automatically in the Road Network feature without any input from the user. Once Intersections are identified, they are listed and managed in the Intersection area of the Road Network: Task Pane.

Edit: Use this button or right-click on the intersection in the project tree and choose Edit Intersection to display the Edit Intersection dialog box and make changes to the Input Data and Output Files for the selected Intersection. Other changes that can be made to the Intersection design are:

1) Changing the Primary/Secondary status of the Roads creating the Intersection,
2) Making design changes that apply to the entire Intersection,
3) Making design changes that apply to one or more Corners of the Intersection.

Reset: Use this button to overwrite all design changes made to the selected Intersection and reset to the original Intersection design.

As stated above, Intersections are created automatically in the Road Network feature without any input from the user. Road Network recognizes and calculates the Intersection using the Centerline (.CL) files associated with the Roads in the Network. If two Roads are added to the Network and they share one or more common point, an Intersection is created and displayed as an Intersection in the Road Network: Task Pane.

For all Intersections, one of the two Roads creating the Intersection will be the “Primary” Road and the other will be the “Secondary” Road. When setting grade through an Intersection, the Primary Road’s Template (.TPL) file takes priority and is used to define the cross-section. The grades of the Secondary Road will adjust to match the Primary Road. Additionally, changes to any of the Primary Road design files – such as the Profile (.PRO) file – will automatically update the affected file(s) of the Secondary Road.

Upon creation of an Intersection, the Road Network feature automatically designates one of the Roads as the Primary Road and the other as Secondary. For four-way Intersections, the first Road added to the Road Network will be deemed the Primary Road and the second Road will be Secondary. For T-Intersections, the Road going straight-through the Intersection will be deemed the Primary Road – even if it’s added to the Network after the Road that stops at the Intersection. The user can change the Primary Road designation in the Edit Intersection dialog box.

Edit Intersection

Picking the Edit button displays the Edit Intersection dialog box which has a Settings tab and, depending on the type of Intersection, 2 or 4 additional tabs – each representing one Corner of the Intersection. The Corner tabs are labeled Front-RightBack-RightFront-Left or Back Left. T-Intersections will have 2 tabs and 4-way Intersections will have 4 tabs.

Intersection Settings

At the top of the Settings tab, the station and elevation of the Intersection is shown for all Roads.

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The Settings Tab of the Edit Intersection Dialog Box

Primary Road: Use the radio button to specify the Primary Road of the Intersection.
Profile Transition PVI Distance: This value represents the distance beyond the edge of pavement of the Primary Road (along the Secondary Road Centerline) that the cross-slope of the Primary Road will be extended.
Profile Transition VC Length: This setting allows the user to specify the length of vertical curve to be inserted at the PVI where the extension of the Primary Road’s cross-slope and the Centerline of the Secondary Road meet.

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“Profile Transition PVI Distance” and “Profile Transition VC Length”

Template ID: This is the point on the cross-section used to define the horizontal (Centerline) and vertical (Profile) alignments around the Corners of the Intersection. Also, the profile for the side road will tie into this Template ID on the main road. The Template ID may be specified as any point on the cross-section – such as edge of pavement (EP) or the back of curb (BC) – as long as it has been defined as a Template ID in all of the Template (.TPL) files used to calculate the Intersection. Type the Template ID in the text box or use the Select button to choose from a list.
Hinge Profile and 2nd ID: For the side road profile, this is an optional second point to match from the main road template.

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Cross-section of main road showing side (alley) profile tying into single Template ID at flow line

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Cross-section of main road showing side (alley) profile tying into Template ID at flow line as well as 2nd Hinge at Right-of-way of main road

Surface Method: See the Transition Defaults section above for details on this setting.
Transition Method: See the Transition Defaults section above for details on this setting.
Link Secondary Centerline for T-Intersection: When this option is enabled, changes to the Centerline (.CL) file of the Primary Road will, if necessary, force the Centerline of the Secondary Road to be extended or trimmed in order to keep the Intersection intact.

Note: The default value for several design criteria such as Intersection radius and length of vertical curve can be set in the Transition Defaults tab of the Road Network: Settings dialog box.

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Corner tabs – Front-Right, Back-Right, Front-Left, Back-Left

Depending on the type of Intersection (“T” or 4-way), there will be either 2 or 4 additional tabs available in this dialog box. Each of these tabs represent a Corner of the Intersection and allows the user to specify horizontal and vertical Input Data and Output Files specifically for that Corner.

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One of the “Corner” Tabs of the Edit Intersection Dialog Box Intersection Input Data

Radius: Use this value to specify the radius of the curve for this Corner of the Intersection. The Intersection Template ID specified in the Intersection Settings tab of this dialog box determines the point on the cross-section being affected by this setting.
Tie to Existing: Enable this option to keep cut and fill slopes from projecting to the existing ground through the Intersection. In areas of steep cut or fill, this setting helps avoid overlapping Road and Intersection tie slopes.
Edit Profile: Pick this button to open the Input-Edit Road Profile Editor and make changes to the Profile for this Corner of the Intersection. The Intersection Template ID specified in the Intersection Settings tab of this dialog box determines the point on the cross-section being represented in the Profile Editor. See Road Network: Road Profile Editor for more Help with this feature.

Reset: Use this button to overwrite all edits to the Profile of the Corner of the Intersection and reset to the original Profile.
Edit Template Transition: Pick this button to display the Edit Intersection Transition dialog box. This allows the user to control the stations for transitioning through the Intersection from a Template on one Road to a different Template on another Road. These Transition stations only apply when the Roads in an Intersection have been assigned different Template (.TPL) files.

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Edit Intersection Transition Dialog Box

In the Intersection Transition Dialog Box... The Starting and Ending Stations of the Intersection transition are displayed at the top of the dialog box.

Transition Starting Station: This is the station at which the Primary Road Template ends.
Transition Ending Station: This is the station at which the Secondary Road starts.

Allow Single VC: When the difference in grade at the Intersection between the Primary Road and the Secondary Road is too severe, two intermediate PVIs must be inserted into the Profile of the Corner of the Intersection in order to properly transition from one Road to another. In some cases, the transition is possible using only one intermediate PVI in the Corner Profile. If this option is enabled and if the intersecting grades allow it, only one intermediate PVI will be inserted. If this option is not enabled, two intermediate PVIs will be inserted regardless of the intersecting grades.
Template Grade Table: Pick this button to select an existing or create a new Template Grade Table (.TGT) file defining the grades for the Corner of the Intersection. This file allows the user to define specific slopes and distances for one or more Template IDs that have been assigned in the Template (.TPL) file. The Edit button opens the Template Grade Table Editor. This Editor is the same as the one used for the Template Grade Table command. Please refer to the Help files for that command if additional assistance is needed.

“L” Intersection with Knuckle: When two centerlines connect at a right angle for an “L” intersection, there is a Use Knuckle option for the outside corner that can be used to make a knuckle bulb.

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Intersection Output Files

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Intersection Output Files

Centerline: Pick this button to output a Centerline (.CL) file representing the horizontal alignment around this Corner of the Intersection. TheIntersection Template ID specified in the Intersection Settings tab determines the point on the cross-section exported to the Centerline (.CL) file.
Profile: Pick this button to output a Profile (.PRO) file representing the vertical alignment around this Corner of the Intersection. The Intersection Template ID specified in the Intersection Settings tab determines the point on the cross-section exported to the Profile (.PRO) file.
Existing Section File: Pick this button to output an Existing Section (.SCT) file for this Corner of the Intersection.
Final Section File: Pick this button to output a Final Section (.SCT) file for this Corner of the Intersection.

Additional Transitions tab

Additional Profile Transition Distance: This option adjusts the transition PVI station on the side profile. The transition station starts as the offset of the Template ID on the main road. The cross slope of the main road is used up to the transition station. For example, if the Template ID is for edge of pavement up to the gutter pan at 11.67 and the side profile needs to match the main crown up the flow line at 13.00, then the Additional Transition Distance should be set to 1.33. Additional CL Distance (Front Main, Back Main, Left Side, Right Side):These options allow you to extend the station range of the intersection. By default the intersection station range is between the PC points where the intersection arcs begin.

Click here to go to Adding and Editing Cul-de-sacs

Recent Posts

Jam proofing drones

“Collect 1 million data points from a 15-minute flight compared to 300 points in a day from a traditional ground survey. It’s no wonder that drones equipped with GPS technology and remote sensors are revolutionising data collection. But will jamming spoil all the fun?”

Who let the drones out?

Recent years have seen the appearance of affordable, high-end drones which, coupled with easy-to-use mission-planning tools, has created the perfect environment in which drones can flourish. No longer the preserve of specialist drone users, applications using drones have been venturing into areas such as survey, inspection and volume analysis with an impact that is little short of revolutionary.

Interference can spoil it all

In the air, the stakes are higher. When things go wrong, the consequences are invariably much more serious than they would have been on the ground. One of the biggest threats to drone safety is GNSS interference. At the very least, disruptions to satellite signals can degrade position quality causing fall-backs from high-precision RTK and PPP modes to less-precise modes. In the most extreme cases, interference can result in complete loss of signal tracking and positioning.

Self interference

A significant source of interference on UAVs is often the other components installed on the UAV. The restricted space means that the GNSS antenna is often in close proximity to other electrical and electronic systems.

gopro_interference (1)

Figure 1: GoPro Hero 2 camera pick-up monitored by an AsteRx4 receiver

Figure 1 shows what happened to the GPS L1-band spectrum when a GoPro camera was installed on a quadcopter close to the GNSS antenna without sufficient shielding. The three peaks are exactly 24 MHz apart pointing to their being harmonics of a 24 MHz signal: the typical frequency for a MMC/SD logging interface.

An AsteRx4 receiver was used in this setup which includes the AIM+ system. As well as mitigating the effects of interference, AIM+ includes a spectrum plot to view the RF input from the antenna in both time and frequency domains. At the installation stage, being able to view the RF spectrum is an invaluable tool for both identifying the source of interference and determining the effectiveness of measures such as modifying the setup or adding shielding. For the quadcopter installation in this example, the loss of RTK was readily diagnosed and solved by placing the camera in a shielded case while the quadcopter was still in the workshop.

External sources of interference

GNSS receivers on-board UAVs can be particularly vulnerable to external sources of interference, be they intentional or not. In the sky, the signals from jammers can propagate over far longer distances than they would be able to on land.

In the case of UAV inspections of wind turbines for example, many countries encourage windmills to be built next to roads, a situation that increases the chance of interference from in-car chirp jammers. These devices though illegal are cheap and can be readily acquired on the internet. Using a chirp jammer, a truck driver can, for example, drive around undetected by the GPS trackers on the truck and car thieves can disable GPS anti-theft devices on stolen vehicles.

External interference: the effect of a chirp jammer on a UAV flight

Although transmitting with a power of around only 10 mW, chirp jammers are powerful enough to knock out GNSS signals in a radius of several hundred metres on land. In the air, the UAV is much more vulnerable as the jamming signals have a far greater reach, unhindered as they are by trees, buildings or other obstacles.

Figure 2 shows how a 10mW chirp jammer can knock out RTK positioning over more than 1 km in a high-end receiver. Even a low-end consumer-grade L1 receiver, being less accurate and thus less sensitive, loses standalone positioning over several hundred metres.

 With AIM+ activated, the AsteRx4 is able to maintain an RTK fix throughout the simulated flight as well as showing no degradation to its position variance. The full details on these simulations can be found in a recent white paper.

Solving interference on UAV systems

A comprehensive approach puts interference considerations at the forefront of receiver design and incorporates it into every stage of signal processing. In the case of the AsteRx4 and AsteRx-m2, the antenna signal is immediately digitised after analogue filtering and automatically cleansed of interference using multiple adaptive filtering stages.

As each interfering signal has its own individual footprint, being able to visualise the RF signal in both time and frequency domains allows drone users to identify sources of self-jamming and adapt their designs accordingly before the drone gets in the air.

When it is in the air, AIM+ is able to mitigate jamming from external sources: a set of configurable notch filters are complemented by an adaptive wideband filter capable of rejecting more complex types of interference such as that from chirp jammers, frequency-hopping signals from DME/TACAN devices as well as high-powered Inmarsat transmitters.

chirp_jammer_interference

Figure 2: RTK position availability for the AsteRx4 with AIM+ activated and a comparable high-end receiver. The low-end receiver tracks L1 only and outputs less-precise standalone positions. A 10mW chirp jammer is located on the ground at position (0,0) as shown.

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