Using Laser Scan Data for Road Rehabilitation

Here is a video I put together showing a use of laser scan data as part of a road rehabilitation workflow.

The background to the workflow is that a section of motorway requires repaving. The repaved section is designed in C3D and is already complete. The design requires that there is adequate vehicle clearance after the section of the road has been repaved. There are a number of overpasses along the motorway which have been surveyed using laser scanners. The workflow in the video demonstrates how to use Autodesk Recap, AutoCAD Civil 3D and Navisworks Manage to perform a clash detection between the clearance envelope and the laser scan data to check for adequate clearance.

The dataset is from the Netherlands so thanks to Peter Ingles of Autodesk for putting it together!

Please make sure that the quality settings are set to the maximum in Youtube when viewing (see small cog/gear symbol in bottom right of screen).

http://youtu.be/u2ddQpuomRU

Urban Overlay

I had a query this week about where you would start when designing an urban overlay in Civil 3D. The design involves planing out and replacement of existing surface with the requirement that we must tie back into existing road levels at the curbs. Desired road crossfall is 2.5% with flexibility to reduce this if required.


Start off by creating your existing ground surface - in my case creating from 3D polylines and AutoCAD blocks representing spot heights. Next create the existing road centreline alignment and profile. (Copy the 3D polyline for road centre and turn it into a 2D polyline - then create alignment from this). Also create existing pavement edge alignments and profiles in the same manner. This is what I have so far...

The subassembly that we are going to use is OverlayCrownBetweenEdges.

Like most subassemblies the layout appearance is not that important but rather the properties of the subassembly.

For a detailed explanation of the behaviour and properties of this subassembly see the help menu. In my case the offset values are going to be controlled by the existing pavement edges - these will be set as targets in the corridor later - and I can ignore the left and right offset properties. I want to achieve a min slope of 2.5% on my finished road surface. The subassembly will examine the existing road surface at each corridor sampling frequency and determine the higher of the control points (pavement edges). It will then apply the min slope from this point back to the centreline and then slope back down to the opposite pavement edge at whatever slope is necessary. Since this slope value will vary and depends on what the existing road surface is like at each sampling frequency you are best to set a relatively high max. slope value. If the slope needed is greater than the max. set in the properties then the corridor will not be created at this point.


I am leaving the crown height value to zero also - setting a value here can override min/max slope values. I want my design parameters based on the slope values only.


When creating the corridor use the existing centreline alignment and profile. In the target mapping dialog box select the alignments and profiles representing existing pavement edge to define the offset and elevation values for the road edges.

The resulting sections look like this...

You can see the result - the existing ground is higher on the LHS, C3D applies the min slope out from this point towards the Cl and then applies whatever slope is necessary to tie back to existing pavement edge. If the slope is too high on the lower side you can easily edit the subassembly properties to reduce the min slope value, or use the corridor cross section editor if you want to modify only a small region.

Copying Superelevation Data Between Alignments

In order to get C3D to automatically apply superelevation (SE) from the design criteria file you will need to have properly defined geometry on your horizontal alignment. That is to say that Civil 3D needs to see transitions and curves on the alignment to automatically apply the SE.


If you are using a surveyed road centreline (for overlay jobs for example) to define your alignment geometry you will probably not have defined curves and transitions on your alignment. This will be usually be the case if you create the alignment from a polyline. The polyline connecting the surveyed points consists of a series of straights. While we might know by looking at the alignment where a curve exists, Civil 3D only sees a series of short straights joining the points and will not be able to apply SE automatically from the design criteria file.


You can add it manually using the SE curve manager. To do this select the alignment and click on Superelevation on the ribbon< Calculate/Edit Superelevation < Open the Superelevation Curve Manager. Here you can manually add SE data. You will need to enter data for each curve and transition manually however which is cumbersome.

An easier way to do this is to create a best fit alignment from your surveyed road centreline, apply SE automatically to this alignment and then copy these values and paste them onto the actual road centreline alignment.


First create an alignment from the surveyed road centreline polyline as before. Then use the create best fit alignment tool to create an alignment from the same polyline. Your best fit alignment will have curves and transitions which you can tweak to match the existing road alignment. You can then apply superlevation to the best fit alignment as you normally would. (Select the alignemnt and click on Superelevation on the ribbon< Calculate/Edit Superelevation < Calculate Superelevation now).


If you then open up the SE tabular editor for the best fit alignment there is a new command (see below) in 2012 that allows you to export SE values to excel file.

Export the SE values from the best fit alignment. Open the tabular editor for the surveyed road centreline alignment and click import. We then have SE values applied to our surveyed road centreline for the existing horizontal geometry.

Customising Cross Sections

A query that has come up regularly (on overlay jobs) is how to display proposed levels on cross sections at specified offsets from the baseline... (and then get them out to csv file)


For this example I am using the UKIE country kit:


First add a new band to your cross section in the section view properties < bands tab - Select the 'Surface Levels at Major Interval (Section 1)' band style from the list as shown and click 'Add'.

Untick 'Match major/minor increments to vertical grid intervals'. Set the 'major interval' for your band to the desired offset. The display of the minor interval labels is turned off by default for this band.

Set the band to read the desired surface and your sections should display levels at offsets from baseline.

While it is one thing to have these levels displayed on cross sections; how do we get them out to csv file for setting out? This takes a bit more working around. There may be an easier way to achieve the following so please post it if you know how...


Create your final corridor with finished ground surface. Create a new assembly. On the 'Generic' tab of the toolpalettes select the 'LinkOffsetonSurface' subassembly and set the following properties:


Offset from Baseline: 2.5m
Point Codes: 2.5m right

Leave other options at default. Build a new (dummy) corridor using this assembly, the road centreline alignment and associated profile. In the corridor properties < parameters tab < set all targets and set the target surface to the surface you want to sample.

Now we can extract the points using reports. In your Toolspace under:  Toolbox tab < Reports Manager < Corridor < use the 'Section Points Report'

In the report dialog box select your dummy corridor (the linkoffsetonsurface one) and you should see your point code listed under the list of features. Set the station interval and click create report. You can then copy from here into excel and edit as necessary.


There are other reports in the toolbox that will produce something similar but i have found this one easiest to edit in excel afterwards. Also as an alternative you could create cogo points from your dummy corridor, place them in a point group and export them directly to csv file. Using the report above produces a better result as it will give points across your corridor at each chainage. Exporting from point group only gives easting northing and not chainage.


Also why not add the linkoffsetonsurface subassembly to your design corridor assembly rather than creating a new assembly for it?


If you add the linkoffsetonsurface subassembly to your design corridor assembly you cannot reference the corridor finished ground surface in the targets. This is because a circular reference will be created – both the corridor and the assembly would be trying to reference objetcs from eachother. The solution is to create a separate assembly as above.


I had originally posted this on the UK & Ireland Civil 3D user forum at http://civil3dukie.com