My name is Chris. I am a city planner and work with an engineering company. We mapped a group of trees near a highway a feww eeks ago, using the Free Trial Pro Version. The drone flied nicely within the prescribed boundaries.
However, we went out and used a hand GPS to map the trees ourselves and compared the results. The Drone Deploy map was off by about a foot.
Our goal is to use Drone Deploy as a mapping system in place of surveyors.
Is the Business package any more accurate? Is it possible to get even more accurate results? Will ground control pints , which are available in the Business package, help us be more accurate?
GCP (Ground Control Points) will significantly improve the accuracy, from feet down to an inch or so. If the area is large, over an acre, you may want to use more than one GCP distributed over the site with equal distance between them and the boundaries (think of placing circles that cover the site with minimum overlap). Place the GCP’s in the clear as much as possible so they show up in as many photos as possible. For this reason do not place them on boundaries unless you are out of other options. I would start with one and go from there.
Search the forum to find additional recommendations.
Try looking at the above to see if it helps.
A handheld survey of trees at the trunk and estimation of the center vs approximation of the trunk from the canopies?
Can you elaborate on the process?
What kind of handheld? Can you replicate your own handheld survey within a foot?
The drone’s GPS is only accurate within a few feet so GCP’s would be necessary for greater consistency and accuracy.
I think we have pretty much beat the GCP horse to death on this one and I don’t necessarily think that it has anything to do with they are wanting to achieve. Honestly I don’t think what they are trying to achieve is even possible. Until We understand the process that they are using for data collection and how they are determining the reference points we will never know on whether the data they’re trying to acquire is even achievable. With or without GCP’s.
Thanks for your answers, everyone. I’m not sure these topics can ever be “beat to death” because there will always be new users coming online with questions. I will take a look at the ground control point process and try that.
Good luck @Chris_Devins_Creativ! I hope I didn’t sound too harsh with the analogy, but the information about accuracy and gcps is widespread and should be pretty easy to find. My point was that the process that you are using needs to be analyzed to make sure that the method has been given the best chance possible to accomplish your goals. Trying to compare a drone survey to a traditional survey is one thing, but a handheld is quite different. If you are just looking for horizontal distances I think you can accomplish that without GCPs. GCPs are meant to tie the survey to the actual global position and provide the ability to use real-world elevations whether it geoid or Surface. I guess most importantly I’m trying to understand how you are locating a tree trunk in the 2D orthomosaic with the canopy? I would also be interested in hearing about the process for locating GCPs with a handheld.
Oh, no problem, Michaell. i appreciate the help. These are freshly planted tree saplings. We plan on counting the more mature trees in the early Spring.
I’m pretty sure they used handheld GPS’.
Thanks @Chris_Devins_Creativ, that definitely helps shed a little bit more light on the situation. I have done a couple of tree surveys with a handheld in the past and learned that I have to get at least three shots from different vantage points to accurately locate the center, especially in our area where we have a lot of multi live oaks. Understanding better what you are locating I would expect more accuracy as well. Are you measuring from planting to planting and inspecting the spacing?
Yes, absolutely. We’ll survey the more mature trees in the fall, when they have no leaves (it’s cold here in the Chicagoland area at that time).
Also, Mike we need GCP’s because we do need to tie the survey to an actual global position and use real-world elevations. We’ve been loading the X,Y’s and Z’s into Arc GIS.
Gotcha. I am in the same boat. I need correct geo-location that ties to the CAD file and the surface benchmarks. Good luck!
So, are we saying here that to use GCP’s, it is first necessary to lay them out and measure distances between them with ground-based GPS equipment?
You lay mats or targets out across the site, record their coordinates using GPS (x,y and z), fly the mission and when uploading the images to DD you are prompted to upload an excel file with the coordinates and mark the centre on each of the targets in the various photos they appear in.
Using GCPs speeds up the processing time through DD and makes the overall map more accurate. I don’t see much change in accuracy on a 2d plane, but it’s the only way to get anything remotely close to being reliable for the z-axis.
Definitely more accurate in x and y in my experience.I will say that because it is a percentage that an isolated area does not benefit much from GCPs. One case would be stockpiles. They are a vs b which when localized is minimal. Where gcps do make a significant difference is over thousands of feet. If you are measuring in comparison to definite contours then you will see the most variance at the midpoint between GCPs. That is what I base my accuracy upon. Right now I am working at plus or minus 2 to 3 in.
Yes, you make a coordinate file to be uploaded along with your pictures. Even people who don’t need glibal association and that don’t have survey gear (except for their drone😉) can use GCPs derived from an already flown map to make future maps repeatably accurate in a relative manner.