Best workflow to create center-line alignment from 15cm aerial imagery for 70km of gravel road

[pdufourUPCTG]

Hi all!

I'm facing a fair easy to understand challenge, but not so easy to solve ..

I've been looking all day for an efficient way to digitize and create center-line alignments that follows near-perfectly 70km of gravel road from high resolution georeferenced imagery.

The deal is that I need those alignments to remain easily editable (I love been able to grip-edit), in case I need to modify some portions of those alignments in the future.

1. I first tried to digitize the center-line with Cogo Points, and use best-fit alignement from 100 CoGo Points - it keeps crashing, doesn't work.
2. I then tried to digitize the center-line with Spline (which followed the center-line near-perfectly) and convert them to polyline (either arc OR line, because having both is impossible).
   1. If the spline is converted to arc only, the resulting alignment is following perfectly the center-line (beautiful), but since it's only composed of fixed curves and NO line at all, any edition of this resulting alignment will break the tangency of those arcs, making it a nightmare to edit, but so far, this is the best compromise I found (following perfectly the center-line, quick to digitize, but not easy to edit).
   2. If the spline is converted to line only, when I create the alignment I choose to insert arc with a radius for tangency, but I then need to manually grip-edit each curved to match the center-line, again - not very efficient. 
   3. I also used the best-fit alignment from polyline - it's good, but not good enough, since I need to re-edit each alignment manually, insert new PI and new curves, try to fit them all - again, not very efficient.
3. I also tried to digitize the center-line by creating a Feature Line with line and arc, which takes too much time, but even that, the resulting alignment is not easily editable. 

By easily editable, I mean this : a surveyor calls you up, the existing road has shifted by a couple of meters or even completely evolved to a new path, and you need to modify those alignments, but your corridor and profiles are already created. Having the ability to grip-edit the alignement has helped me in the past.

For your information, profiles and corridors will then be created for all those alignments - if the created alignement is slightly off the center-line, the corridor won't match the LiDAR surface data greatly impacting the resulting quantities (see sketch goal attached). This is for a wind-farm project. Maybe this is overkill, maybe not.

Please, do you have any ideas?

[brian.strandberg]

This is definitely an interesting challenge.  I like your option 1, the best fit based on cogo points.  I'm wondering why its crashing, if you copy those points into a blank drawing does it do that?

I agree with you wanting to stay away from splines, they introduce too many issues.  

I'm wondering if AutoCAD Raster Design can help you here.  I'm not an expert with it, you may want to post your question on that forum as well.  Here are a couple of resources: https://help.autodesk.com/view/RSTR/2023/ENU/?guid=GUID-19AEC508-7CAD-4CED-9711-3FC1C5A0D13F

and https://help.autodesk.com/view/RSTR/2023/ENU/?guid=GUID-0D28B35C-966A-43CB-B5BB-C10A98CBAF10

[AllenJessup · Accepted solution]

I'd be tempted to trace it using lines and arcs. Then convert them into an Alignment.

There's a trick in Autocad. Draw a line then start the Arc command. When asked for the first point for the arc hit enter then pick the endpoint. The arc will be created tangent to the line.

The same with a line. Start the line command right after drawing an arc and hit enter for the first point. The line will be tangent to the arc.

[neilyj666 · Accepted solution]

I do a lot of windfarm work typically in existing forest as you show (but rarely with the luxury of 15cm data and not 70km of track...!!!). My workflow is similar to that as suggested by @AllenJessup but the other methods I have used are

1. Create polylines and add arcs as I go to get the best fit for the centreline (which is just eyeballed but if you don't have the track edges this could be the only option)
   
   
2. Create alignments using lines and add the curves afterwards

The first method is my more usual method as the grip editing is better but as a caution, forest tracks are typically 3.4m (in the UK) and the wind turbine delivery vehicles usually require at least 5m width and from your sketch you will need to be flexible to move the track into a cut situation rather than a possibly problematic fill.    

[Joe-Bouza]

why don’t you just draw the alignment.? You have already accepted that you will go back and edit. Draw an tweak

[lim.wendy]

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[pdufourUPCTG]

Thanks you @Anonymous
I'll take a look into Raster Design.
There might be some options there to vectorize a raster from pixels value, since the roads are more white than green.
I tried to isolate cogo points in a new drawings, and it kept crashing.

[pdufourUPCTG]

That would work and I would accept this as solution.
It might takes time to draw them accurately, since its not always obvious where the arc ends.
I found that tracing a spline before right in the center gives a better chance to effectively trace the arc and line following the spline.
Thanks you @Anonymous

[pdufourUPCTG]

Thanks you @neilyj
I usually do your 2) option too by creating a polyline along the path, letting C3D insert tangeant curve and then, grip-edit them.
I will go with the 1) option though.
You are right. Vestas V-162 here in Canada, needs also at least 6.0m of track. Usually, once the alignment is created, I create an existing ground profile and a design profile with Kcrest and Kcurve civil parameter of the Vestas. Once the corridor is modeled, I validate and analyse each section in the corridor section view. What I haven't explored yet is the optimization potential of those designed profiles (Haul Diagram, Softree software) - sometime, it's better to create a CUT to provide materials to the next FILL to avoid long hauling, but this is another topics.

[pdufourUPCTG]

Thanks you @Anonymous
In fact, that would work too.
Plus, there are best-fit options available.
Great idea.

[neilyj666]

@pdufourUPCTG Only done modelling for the V150 in the UK not the V162 (usually public road access issues for the large blades is the major constraint). 

Mass haul is indeed an whole topic of its own and I wish the mass haul diagrams in Civil were a lot more useful - I typically use Excel, CAD and manual judgement which is very tedious...!!!!!

[Joe-Bouza]

Right. The point being, you know you will have to edit, so why bother with the native objects (Sorry @AllenJessup )

the alignment natural draws tangent to arcs. Then can be push pulled as needed without upsetting the apple cart.

[AllenJessup]

@Joe-Bouza  No worries Joe. In the end creating an Alignment from the start is a better workflow. However I, and maybe some others, think in AutoCAD first.

In some cases I've seen people wade through three of four dialog boxes to get to what you could get with a simple AutoCAD command.

[nostupidquestions]

70km is like 45 miles? I would break it up into pieces. Do you have a r/w you are following? I did a 5 mile piece of existing road that I had to recreate the centerline because there was no recorded r/w. I just traced the centerline as best I could with a polyline then converted to an alignment then added the radii. Easy to draw a polyline and convert to an alignment than try to draw an alignment. Good luck.

[neilyj666]

@nostupidquestions It will, in all probability,  be broken up into natural sections i.e. main spine(s) and spur roads to the various turbines so totalling 70km.

@pdufourUPCTG I would certainly suggest having several corridors (although I create a single corridor with multiple baselines for the windfarms I design but they don't usually get above 20km total)

[pdufourUPCTG]

Thanks you @nostupidquestion
Good idea to use a R/W, but no I don't have any.
I will certainly chunk them into pieces, thanks!