We are going to be topoing a large area (about 400 acres) of subgrade to determine D1 quantities for final grade. It's a large area so small variations matter. I'm attempting to rig up a continuous HA/HT measuring device. I would like to be able to drive along with this device mounted under (it doesn't have to be exactly under) the antenna or prism and get a continuous HA/HT fed to my controller with bluetooth (or serial). I suspect that someone here has already done this. The advantage of this is that it doesn’t matter what the suspension of the vehicle is doing – the HA/HT would always be valid.
My plan was to use a handheld style distance measurer (like the disto) to continuously measure the HA/HT. Some Leica Distos and the Bosch GLM100C (probably others) will transmit the measurement via bluetooth and will measure continuously*. They define continuously as repeatedly for a fixed period of time (like 1.5 - 5 minutes).
Our Leica rep says the Distos can't be made to continuously measure (auto laser shutoff).
The Bosch stops after 5 minutes.
The Spectra Precision QM units don’t look like they can communicate
The second obstacle is power: I need these to run all day (replaceable batteries would solve that but the devices with communications have had internal batteries.
I see that the pieces and parts to build your own laser measurer are available on line but I don't want to have to defend that piece of equipment if (when) the contractor disagrees with the quantities. We'll provide a volumetric estimate of accuracy so that the contractor can factor that in their bid.
An alternative approach is to construct a prism/antenna mount on a rigid bicycle fork that rolls on a 2.25" x 29" mountain bike tire. This would work but would be quite the contraption - not nearly as portable as a disto type solution.
I’ve done a bit of research but I might have missed it: Am I missing an out-of-the-box solution to this problem?
Has anybody built a continuously reading HA/HT device similar to this?
If so, what did you do and how did it work?
Thanks for your help.
I have yet to see auto topo with less error than the suspension travel of our ATV. point being any error you eliminate will be swallowed rather quickly...
Thanks for the feedback.
I agree that kinematic GPS vertical error is similar to ATV suspension travel on mildly undulating surfaces. No doubt: GPS isn't the best tool for tight vertical measurements.(For the purposes of this thread, let's not bring up issues with geoids). Total station vertical accuracy is significantly better than GPS when using ATR (assuming the instrument is calibrated and conditions are appropriate for the distance being shot).
Any vertical movement (suspension or ??) adds to the total error when unaccounted for. You'll get a better answer by accounting for and reducing/eliminating any error source that you can. The error that exists will be easier to quantify.
In addition to getting a better answer, when you remove (from a practical standpoint) HA/HT error: you remove one argument from the list of arguments that the contractor can potentially prevail on.
I've read about similar devices that have been used in deformation studies/monitoring - these were stationary and measured with far greater precision (and cost) than I'm looking for.
I've built the bike idea you are describing. Took the whole front fork and kept the handlebar, turned down for a grip. I extended it up to 2m with a range pole and clamped on a rod level. Work very well, and should have patented it long ago!
Neil
Did you mount it to any type of vehicle or was it for wheeling around by hand?
Any photos?
JK
I surveyed a couple landfill caps using the total station tracking a prism mounted to the roof of a Jeep Cherokee. Worked very slick and was sufficient to calculate quantities for payment. It made gathering a 50' grid of shots over 15 acres quick work.
We used the short vehicle magnet mount from a Trimble Pro XRS GPS set up and mounted the 360° RMT prism directly to it.
I was unsure about how much the vehicle suspension was going to affect the elevations and how we were going to be able to determine the prism height accurately.
The only answer was to do a trial. We measured the height of the prism as best we could and slowly drove a grid pattern while the instrument took shots every 50' We then staked the points out using a rod with a topo foot we made out of conduit fittings.
We quickly noticed that we were getting a fill value on all the shots. We averaged a half dozen of the fill values, adjusted our "Rod Ht." and gathered another bunch of data. This time when we staked the points out, we were hitting the elevations within hundredths (bouncing back and forth between cuts and fills). We decided that the amount or error we were seeing was similar to the undulations in the terrain.
As a check and to provide redundancy, we sprayed a series of check shots over the land fill cap using a rod.
When the data was reduced and the check shots were compared to the final surface model, I was very pleased with the results.
I would definitely do this again if the conditions were right (smooth, fairly level, open terrain).
May be the dumbist idea out there. But what about making a tow behind unit from on old 4 wheeler axle, then adding a few hundred pounds of ballast to keep bouncing to a minimum.
If you are worried about movement in a suspension, I wondered about the problem of keeping the antenna rod vertical.
You're okay with a moderate height and reasonably flat terrain. If your buggy encounters a 12% slope (actually 1 in 8.6) with a 6 ft rod length, the top is off 0.7 ft and the actual height is 5.96 ft. I found the 0.04 !
What you need is a Sonic Laser which is very common in the paving industry.
Sonic Averaging System (SAS)
Industry’s first choice as a non-contacting system
Continuously measure the elevation over the surface
Automatically averages and adjusts tow point cylinder.
The SAS is convenient, maneuverable and produces a great finished surface.
imaudigger - those are basically the conditions that we're supposed to have - smooth (graded and rolled), open, and relatively level. We've used the approach you took and the results were also good.
SC Crew Chief - The compressed suspension would definitely reduce vertical movement.
Bill93 - vertical rod won't be an issue on this particular job. If I had my continuously measuring HA/HT device via disto-type laser, a gimbal mount would resolve that.
Leegreen - I'll have to look into that more. I see that the Sonic Tracker II would be the needed sensor and is typically part of the topcon Smoothtrac system. I didn't find an owners manual or specific info on the Sonic Tracker II on the topcon website. I'll contact our topcon dealer to find out if the Sonic Tracker will work independently of the Smoothtrac system and what type of output I can get in a non-Smoothrac environment. I like that the Sonic Tracker is ruggedized and sealed.
On this project, the top/toe of embankment top will need to be accurately (+/- 0.2' hz and +/-0.1’ vert) defined. We can't drive directly on the edge with a truck or ATV because of the potential slope damage so I'll need to mount the antenna/prism on an arm that extends out a couple of feet. We’ll drive with the arm directly over the edge so that I can get shots right on the shoulder while driving on more stable ground. If I can eliminate the majority of the HA/HT error, my error budget will tolerate kinemetic GPS. I'd really like to drive a vehicle with plush suspension gathering kinematic data and not have to worry about antenna height - just read, feed, and apply. My experience shows that less vibration at the GPS antenna = better kinematic results.
This is basically like a hydrographic survey – I just need a digital fathometer that works on dry land and talks to my controller – an ASCII NEMA String over a serial port or via bluetooth would do the job.
Just a side note to my earlier comment - We utilized the vehicle mount for the large expanse of flatter ground. When it came to the hinge and the fill slopes, we ran around with the rod and ran break lines traditionally.
Just curious, how large of a landfill are you surveying?
I would be surprised if there isn't a commercial version of the contraption you are considering building.
How could flying this not be cheaper?
(Either with Lidar or photo?)
Just curious.
imaudigger - I would think there would be a commercial version too. That’s why I’m asking for the help of the forum… somebody will know if there is a commercial product. I don't want to spend my time or our staff's time reinventing/creating – that’s always expensive. Additionally, I prefer something that has been used by others and is unlikely to be questioned.
The site is not a landfill. It’s a corridor – 32 miles long. It’s brushed about 100’ wide and we are topoing a swath that is about 45’ wide as well as a few pads.
dmyhill - The first thing we did was to investigate a LiDAR solution. We obtained a magnitude of effort estimate for a TIN surface with accuracy better than +/-0.3’ with control and QC for the first 12 miles of the corridor. In AK, for this task, the LiDAR solution isn’t cheaper...yet. Additionally, the LiDAR/photo solution has a longer delivery time.
P.S. The LiDAR provider had the option of using photogrammetry if it was more cost effective.
Sure, See attached file, I had the nephew model it for us.
I turned the handlebars down to get a comfortable grip arc, and I even left the front handbrake on, just in case I topo-ed too fast!?! I pumped the tire up hard, then calibrated it to a 2m height. You can clamp your DC on just like a normal rod, and this one has got to roll 100 times better then the ones I see in the survey catalog with the small 4 or 6" wheels.
The job I was working on was too steep for motorized use, so I walked it. It worked very well.
For a rough topo, we were thinking about putting the rover on a pole clamped to the ATV, and then putting a wood block in the suspension on that corner and cinching it tight with a strap. A over-inflated tire is not going to flex enough to worry about on dirt work.
