02/08/2020
TerraForm 3D Inc is now offering 3D data collection service utilizing drone-based LIDAR. TerraForm 3D will fly your project to collect LIDAR data that will then be processed to extract a ground surface to be used to calculate earthwork quantities, view contour maps and decide how to possibly develop your property. Data can also be used to calculate volumes of earth moved for a progress report for billing purposes as your project progresses as well as collecting data to verify the As-built to ensure the project was finished as designed.
My goal is to provide 3D data:
1. To clients that need this data for developing commercial, residential and private projects.
2. At a faster rate than they would with normal data collection crews.
3. In areas that would be time consuming due to terrain and vegetation issues that may need clearing to provide access lanes for conventional survey methods.
4. In a safer way where crews are not having to deal with uneven, wet or hazardous terrain or with wildlife that crews may come across by being “on-ground”.
Other uses for LiDAR:
*CRP areas that the landowner is considering leveling or developing after the contract has expired.
*Collecting data for existing builds and roads to draw out and/or measure objects.
*Flying powerlines to determine vegetation height underneath the lines. Also to measure the sag in the powerlines when they are being built or on older lines to determine the quality on the line.
There are numerous uses for LiDAR on drones.
I am using a Microdrones mdLidar1000. The LIDAR unit is capable of collecting approximately 40-160 data points per meter square(approx. 39” x 39”). This will depend on how high you fly, the amount of overlap and how fast you fly. Different conditions call for different flying parameters. Even on small acreage you can get millions of data points. Many more than those collected by conventional means.
Once the flight(s) are finished, I process the LiDAR data to correct the errors of the flight. The flight is autonomous so you have to post-process the data to get down to sub 6cm vertical accuracy. Then in another program I process the corrected data to extract a clean ground surface by removing the trees and small vegetation. Deliverables to a client will be determined on what their needs are for the project. This could be a cleaned up .las file for them to generate their own surface, giving them a surface or contours on the required spacing in a variety of formats.
The data can be collected over various areas from an open field up to a wooded tract of land. Where it is really invaluable is in areas of heavy vegetation and trees that would make it laborious, time consuming and expensive to try to get good data for a terrain model.
The first example is an 18 acre project with trees covering most of it and small scrub brush on the remaining areas.
This project took about 30 mins to fly then about an hour or so to collect the RTK GPS points by walking in the trees. Using the RTK GPS in the trees takes a while because you must wait several minutes for the receiver to re-initialize under the canopy. When you view the results, you will see point comparisons are fairly tight considering the canopy.
I have images attached below for both examples that show point comparisons and the type of tree coverage in the first example.
The second example is where I had surveyed a 60 acre tract of farmland with RTK GPS using a truck. I surveyed it the previous year but due to weather conditions it was never leveled. I surveyed it the following year with the LiDAR drone. Same ground conditions as the RTK GPS. Plowed field so the surface was not smooth. The land leveler had started moving some of the dirt but only worked a few hours. There was minimal amount of dirt moved and all remained in the field.
I flew the field then set out about 17 ground truth points to compare the corrected LiDAR data to the RTK GPS elevations at each ground truth point. This was by using the surface from the corrected and filtered LiDAR data.
I imported the final LiDAR data into my land leveling design program and designed the LiDAR survey exactly as I had designed the RTK GPS survey.
I have images showing the cut-fill map of both the LiDAR design and the RTK GPS design. Some things to note when looking at these pictures. In the NW corner of the field you will see a difference in the cut-fill shading. This is where the earth moving was done between the two surveys. But none was moved out of the field. Look at the total yardage moved in each picture. The difference is about 874 yards overall. There is a little over an acre difference in total acres. This is because the land owner had cleaned out a ditch on the E side after the initial survey and I removed that area since the spoil was still there.
Also, the two surveys were done using the same control point meaning each has the same starting coordinates in the XYZ. There is about .06’ difference between the finished design elevation of each design. The design elevation of any given point in the RTK GPS survey using the truck is lower by this amount when comparing the same coordinate in the LiDAR design. In my opinion this is because the truck was packing the plowed ground(fluff) back down closer to natural ground(compaction). The LiDAR scans what is on the ground. In this case it would be the plowed ground(fluff). No compaction.
So the design elevations are a little different but the overall yardage to be moved is within a reasonable quantity. If you calculate .01’ of dirt across 59.5 acres that is about 960 yards of dirt. This scenario is slightly less than that.
The image showing the ground truth points will show the difference between the LiDAR existing surface and the RTK GPS data points collected. You will see a few that are out of line with the majority of the others but remember the LiDAR picks up everything. Even the undulation of the plowed field(fluff). When I sat my pole down on the ground there were clods of dirt all around it. Not a smooth surface.
But when you average all the data points of each survey together and compare them, you see the difference between the two modes of surveying.
You will see that they are typically within .15. LiDAR is not accurate as RTK GPS but in certain environments and terrains is pretty close if not better because of the time it saves, the ability to scan every square foot and the amount of data you can collect.
In the attached images you will see:
First example
Point cloud of existing treess.
Point cloud of extracted ground.
3D surface with contour overlay
Point to surface comparison of tree survey.
Second example
RTK GPS survey cut-fill map showing total yards
LiDAR sruvey cut-fill map showing total yards
Point to surface comaprison
