Surveying a Road or Highway using Altus NR3 RTK GNSS and Carlson software
When training new GPS users, I was embarrassed to tell surveyors how they should conduct a survey. However, after reviewing my training I realized this HOWTO is necessary to rectify any misunderstandings; sometimes my Australian English Accent creates problems…I apologize!
Let us now look at some ways of modifying existing surveying techniques to achieve higher quality road designs
“…we Support and we Care!”
As technology advances; the methods and techniques used by the Surveyor should change also.
In life before RTK GPS, road design surveys were performed using a Total Station.
Using a Total Station, surveyors recorded points in rows perpendicular to the centerline at linear spacing determined by the distance between section stations as required by the road design team.
Surveying with an RTK GNSS system, we can use a slightly different approach.
Autodesk Civil 3D and Carlson Civil use a surface model (triangulated irregular network) in road design processes.
When using Carlson Civil especially, Sections are created programmatically at a linear spacing set during Road Network configuration; user defined station intervals.
Configuration determines the linear spacing and the road template determines the “shape” of the roadway sections produced by comparing the surface models (existing and final road design).
The keyword here is “IRREGULAR”.
To produce a representative surface model of the road corridor we need the data to be surveyed at “irregular” intervals for best design practice and to create a more accurate design.
As a result of the following survey processes, the surveying job will be performed faster and easier.
Q: What is the advantage of GPS surveying?
A: The surveyor collects more “useful” points faster; using Septentrio/Altus RTK GNSS equipment the Point Store process is much faster and with higher accuracy.
We do not collect LESS data, we collect MORE IRREGULAR spaced data to produce a more representative surface model across the design corridor.
The following STEPS will take you through the processes:
Click the Button below to download the Draw CL .fcl file and copy or move to C:\Carlson Projects folder\Settings.
Copy the Draw CL.fcl file to the Programs/SurvCE/Data folder on the Controller.
The file has been configured to automatically connect all the CL points with a polyline as the Points are Store(d). This polyline is utilized as both the centerline polyline to create a Centerline File in Carlson Civil and also allows us to produce line work to create a “visual” road corridor on the controller to assist the surveyor in following the lateral and linear spacing of data points.
Start SurvCE on the controller.
Select Feature Code List
Select Draw CL.fcl
If you wish to view/change the characteristics of the polyline…
Click Green tick to save changes or Red Cross to leave settings unchanged. These features can be changed at any time during a survey…we advise to make changes before or after survey.
Select the Orange arrow to return to Files tab
SurvCE automatically reads the Draw CL file when Store(ing) Points.
This Feature Code List file will load as the Default until you select an alternative Feature Code List file in the future should you develop advanced techniques or methods.
To test and validate this new method of surveying a road, set up the RTK GNSS receivers in an area near the office or anywhere there is a road or track to survey.
Name a “new” project.
From Survey tab
Record CL (description) points along the centerline of a track/road.
Notice as CL points are stored the points are connected with a polyline. The line is drawn automatically to a DWG file on the controller in Data folder with the “project” file name along with the “project” CRD file.
When recording the start and end of an existing pavement, record the point twice: once with CL description and second with SXP (start of existing pavement) or EXP (end of existing pavement). This will ensure we have a continuous line connecting all (CL) centerline points but still identifying other information points as we survey. It is OK to store “other” points with “other” descriptions along the CL path. Only those with CL description will be joined.
Continue recording points at each change of direction along the centerline.
On completion of the centerline survey
Exit from the Store Points screen (X).
Select the “Globe” symbol (Map/CAD program) in the top right hand corner.
Select Draw from the menu
Select Offset, then 2D.
Set the distance to 8.00m (or the maximum distance used to define the road corridor – 7.5-10.0m).
Select the polyline (centerline) and “click” screen to one side of the polyline.
Repeat Offset command from the Draw menu to offset a polyline on the other side.
We have created a corridor representing the lateral extent of the road survey
Click (X) to exit the Map screen
Select Survey tab
Store Points screen.
Continue the survey, collecting points at around 25 meter intervals to create an irregular pattern using the polylines either side of the centerline to guide the survey extremities, collect random points at “irregular” intervals/spacing.
When collecting the points always consider variations in height these points build an accurate surface model of the road corridor.
This concludes the survey.
Back in the Office
Create a C:\Carlson Projects\”project” folder
Download the ”project” CDR, DWG and or DXF files from the controller to the C:\Carlson Projects\”project” folder.
Start Carlson Civil
From Files menu
Open the “project”.dwg or “project”.dxf from the controller
SaveAs C:\Carlson Projects”project”\”project name” to the project naming standard.
When the drawing has loaded
The screen will display the centerline and the two “offset” lines.
Erase the two offset lines (no longer required).
From Points Menu
Set Coordinate file
Draw Locate Points
Save the drawing
If the centerline was surveyed in the “wrong direction”
From Edit menu
Select Polyline Utilities
Click the centerline (the dashed arrows indicate the current direction of the polyline)
Click again to reverse, again to return to original direction
Esc to maintain “new” direction.
This function allows the surveyor to select/change the direction of the polyline to starting Station 0+00 at the chosen end. Surveyors are free to survey in either direction making the final decision for direction from the desktop.
From Surface menu
Triangulate and Contour
Tick Draw Triangle lines
Set and name the NEW surface file to Original Surface (original)
To remove Contours and Triangle lines; when satisfied the road corridor is sufficiently populated with points
Select Triangulate and Contour
Deselect Contours and Draw Triangle lines
Save the drawing
From the View menu
From Surface File
View the 3D model.
The 3D model will show a smoother irregular pattern representing the road corridor.
If you wish to double check the road design at completion
Select Triangulate and Contour
Select Draw Triangle lines
ADDING MORE POINTS TO EXISTING SURVEY
If you have existing road surveys (CRD) where you feel additional points would improve the quality of the road design. The following will make the process easier.
Draw Locate Points in Carlson Civil or Import the ASCII file into Civil 3D
After connecting the CL points with a polyline,
Offset the polyline with two corridor lines (distances as above).
At the Command line
At the prompt type “file name”
Select the three polylines
Copy the DXF file to the SurvCE\Data folder on the controller.
Ignore and/or cancel equipment setup prompts
Open the Job
Click the Map symbol
Choose the “file name”.dxf file
The polylines will be displayed as a background to the survey data already recorded.
When the survey is (re)commenced the lines will be a survey guide as per the method explained above.