This week I spent some time looking at the data modeling needs for the Wirtgen Slipform Paver for C&G operations. In this post I am capturing what I have found out and next week I will post a video that covers best practices to meet the needs.
- Wirtgen AutoPilot uses a DXF file on the machine
- The DXF File has one layer of data on which each curbline to be paved is represented by 2 lines
- Line 1 is a 2D Curvilinear Line (it has no elevation) and contains the straight and arc elements of the curb line and is used for guidance horizontally.
- Line 2 is a 3D polyline that will be chorded and this will provide the vertical guidance for the machine.
Note that in TBC the linework needed can be represented by a single linestring that contains both the horizontal and vertical geometry in one line, however because the Wirtgen Machine requires 2 lines for every curb you will need to take your 3D linestings and make a copy of them and make the copy 2D. Note that both lines need to be on the same layer in the DXF file (based on what I am told - it would be more convenient if the two lines could be on two layers one for HZ and one for VT so if the single layer is not 100% correct please let me know as we have no way to validate that.
When TBC exports a DXF file you have choices on how to export 3D linestrings - you can export them as 2D (in which case the Z is removed and the 2D line and arc elements are exported, or you can export them as 3D in which case the curvilinear geometry is lost and the lines will be chorded based on the “curve to chord” breakline approximation settings to create a more densely chorded 3D polyline that “accurately represents” the original 3D linestring geometry. The latter option is good for the Vertical Geometry required by the Wirtgen machine, the former option is good for the horizontal Geometry required by the Wirtgen machine. So this means iuf you have a 2D line of true arc and line geometry plus a 3D linestring, if you output 3D lines as 3D then you should get exactly what you need in the resulting DXF file when you run the standard TBC DXF export command.
Couple of extra points
- When you have a closed line like a Hot Dog island, it is recommended that you trim 0.02’ off the end of the line so that the ,line is not actually a closed line - it is better if all lines have a true start and a true end point not a closed loop.
- When you have lines that are ready for curbing, while Wirtgen stated that a Lead in and Lead out line is not necessary for them, everyone else I spoke to stated that a lead in / lead out line for the machine operators to get the machine on line and grade before they start paving is best practice.
- When you have a closed loop (with the 0.02’ adjustment above), and you want a Lead in line, then you can create a lead in line that comes in tangentially to the start of line, but sometimes you should keep these lead ins as a separate line so that the operator then selects the curb line when they get to the point where they want to start paving.
My Wirtgen contact stated that the Wirtgen Autopilot system is trying to create a virtual stringline so that the process of curbing is exactly the same for their users as it was when they set stringlines first and then paved. Their linework model through DXF format is replicating that and the operators can adjust elevations of the Vertical control line or add in elevation points to that to smooth out a high spot etc. as needed in the field.
One last comment on the machine operations, people told me that the horizontal steering tuning of the Wirtgen Machines is typically good and doesn’t normally need much adjustment, however if you are seeing vertical deviations then you may need to tune the vertical of the machine - I don’t know how that works and am not trying to provide Wirtgen machine control support here, the Wirtgen team said to contact them for help and assistance when needed.
I would like to thank the following people for their help and input on this post, I could not have created this post without your help - much appreciated.
- Ben Krebs - Trimble Machine Control Specialist
- Brian Girouard - Trimble Machine Control Specialist
- Jacob Daniels - Independent Machine Control and Data Specialist
- Reggie Schlieper - Flores Automation Machine Control Specialist
- Kevin Garcia - Trimble Specialist Construction Team Manager
- Erik Smydra - Wirtgen Machine Control Specialist
Appreciate all of your support guys - it is great to have you all on Speed Dial
Best Regards
Alan