Does anyone remember the old rule of thumb for topo. Something like a 100' grid will give you 90%, 50' grid 95%, 25' grid 96% and so on. I know those numbers aren't the correct ones, but I just had a bit of a frustrating meeting with some developers. I didn't break out that rule of thumb since I don't remember it.
90% of what?
volume accuracy
Oh.
How much of a penny pincher are you dealing with if they're looking to shave off like 30 minutes of topo work?
I did a calculation along these lines once and it ended up being a laughably small amount of time saved by doing fewer shots.
Well, if it's a 20 mg file and now a 950mg file it's probably adding up to 10 hours of processing, transferring back and forth and at the end of the day there is 20 yards of dirt difference out of 10,000. There's always been a calculation for diminishing returns on dirt, not so much in this day and age but when they are complaining about tire tracks not showing......, well it's a lack of perspective.
I guess I’d never seen it as a rule of thumb like that. I’d like to hear more and know more about any other parameters to it.
That is were experience comes in.
Now is the time for all good men to come to the aid of their country. Typing class 9th grade!
It's a bummer seeing people waste money, but I'm not going to spend much time talking myself out of profit. Say your piece once, then charge a PITA fee plus the actual cost and make some money.
We may be seeing the long anticipated increase in surveyor pay in NC. Folks are having trouble getting surveyors to call them back let alone perform the work. Clients also haven't been complaining about inflation adjusted fees I'd wouldn't dare propose just a couple years ago. Don't get frustrated with your clients, just raise your rates. I met a contractor who showed me a picture of his small yacht named Change Order. While I don't condone extortion, there's no reason a PLS needs to fall on his sword when his good faith efforts reveal greater project complexity than could reasonably be assumed prior to the commencement of work.
The old ways to topo general ground areas were tables, cross-sections, ect. Then came along total stations, computers, breaklines. I would say around 1984-1985 with the advent of "mini-towers" and computerized systems it was all "hands free" calculations, disconnected from stations, offsets. I'm mostly discussing bigger projects, mine reclamation, reservoir construction, highway corridors.
House, small development topos are different cause of required intense details. But the idea was if you grid a site at 100' that probably won't capture enough detail on general ground to keep the design and subsequent finished topo surface will miss too much volume for pay calculations.
If I remember the numbers were something like 100' grid=90%, 50' grid=96%, 25' grid=96.5%, 10' grid=97%, 5" grid =97.2%. Anyway the exercise showed that there is a point of diminishing return respective to the density of the captured topo data. Of course, the OG conditions were paramount, a highly broken site made all that irrelevant.
We finished a drone topo and gave the client an XML file. The site is 260 acres with 80 being the area of interest because it was recently disturbed during a construction project. The client was mostly happy, but they did say features such as windrows along the top of the topsoil pile didn't show up in the contours. So, we densified the points and now the wobble shows up better for the contours over the windrows, a few little piles now pop out, but the XML file is up to 1 gig. I'm quite dubious that what was accomplished was anything useful.
When I did a topo it was always a 25' grid (easy with the GPS display), all break lines, and extra shots to show contours of any piles of dirt. It was my philosophy that the drawing should look like the site. I did the grid shots first so I could learn where the break lines were needed, and I used codes NG for natural ground to plot to the tenth; pav, swk, xtc, and xg to plot to the hundredth; x1 and x2 for extra shots to make it easy to freeze that layer.
Can we all just acknowledge that our best surveying/ mapping methods will never be as “accurate” as their load count quantities? 🤣 🤣 🤣 🤣
Yeah, I'm still kind of a negative nancy when it comes to drone work. Client doesn't know what they're looking at but they know it's wrong and ask for more detail? 🙄
When I did a topo it was always a 25' grid (easy with the GPS display)
That's how I would do it with continuous topo on the 4 wheeler. Often, I could pick out a horizon feature to drive to both ways, it's remarkable how parallel you could get the random lines. Add in Break lines, fill in with flow lines and random topo shots. If there was a hump, hit it with a bunch of shots. I'll have to ask my drone guy how dense the first run was, but now it must be a foot grid, I doubt anything was gained. I head calc. the windrows and came up with about 2-3 yds for each time 4.
I was never a fan of a grid. I just took shots where I thought they needed to be. There might be places they need to be 10 feet apart and other places 100 feet.
I always tried to stay away from volume work.
@david-livingstone totally agree with you on that.
I've had projects before where it was was gently rolling countryside and there really weren't obvious grade breaks. On those I'd do a grid and the way that made it easy for me was to offset a property line or section line I tied on one side of the property every 50 feet across the entire site and walk up and down those lines.
I am not a fan of Grid based acquisition. Nowadays it's obsolete and is low on the hierarchy of importance. When we did grid based topo, the grid spacing was always a maximum assuming there was no significant grade breaks in between. If there is, shoot it. Nowadays we fly and densify the data to meet our needs.
The first large volume survey I performed as an entry level surveyor provided an opportunity to compare the results of a 100' grid topo to the same exact area located along breaklines. My PLS was a bit of a jerk in that he provided no guidance other than to belittle all of us for not knowing what what he'd learned over fifty years of surveying in the White Mountains region of NH. It took me and a coworker two days to run breaklines throughout the sandpit and when my PLS found out he was furious as his son, who was bi-polar and had been fired for attacking another crew member with a machete, could typically perform a 100' grid survey of the sandpit in a single day. We were told to go back out and resurvey it with a 100' grid of calculated points. My "mistake" yielded some interesting results, though I can't remember any of the specific quantities. The breakline survey was significantly more accurate by the coarse metric of knowledge of the site topography and photographs. The sandpit owner had left numerous single dump piles onsite and these clearly showed up with the breakline survey. I also remember that I messed up building a LandDesktop 2004 surface by not incorporating the breakline polylines and that the volumes calculated without polyline breaklines, but with the breakline points, were surprisingly similar.
Now I use LiDAR drones for the vast majority of topographic surveys. It's a $40K-$80K investment and a big learning curve, but the ability to topo hundreds of acres in a day with 0.25' accuracy or better at 95% is a game changer. I'll even fly 10 acre sites as the time lost processing is recaptured through the use of the orthoimage for digitizing roads, structures, tree lines, etc.. Modern software allows for the reduction of point cloud density along planes while preserving density along grade breaks such as ditches and streams. I've even used LiDAR to find an old road bed that represented the best evidence of a vaguely described access easement. Likely similar to the archeological surveys performed with LiDAR, dense vegetation had obscured the road, but a relatively inexpensive five-return LiDAR sensor made the road pop. The only negative feedback I've received from LiDAR topos came from a PE who didn't like the fractal look of the contours. He wanted them to look smoother.
I also remember that I messed up building a LandDesktop 2004 surface by not incorporating the breakline polylines and that the volumes calculated without polyline breaklines, but with the breakline points, were surprisingly similar.
I came along after LDD but that doesn't sound very surprising to me. The TIN should be point to point whether you use breaklines or not. Even if I made the same mistake in Civil 3D it didn't seem like I had to flip a ton of faces to get the surface right.