How do check points validate the accuracy of a map? And how do you use them?
Check points are surveyed points just like GCPs. The only difference between the 2 are that you tell the processor to scale the point cloud based upon the GCPs but not the check points.
After your point cloud is generated, you locate a check point and compare it’s coordinates as reported by the point cloud with the known surveyed coordinates and the differential between the 2 represents your accuracy.
The mechanics of how you do that varies by specific software.
Thank you Sir! What software would you recommend?
Most licences surveyors I spoke with say they can NOT validate the GCPs with out doing it them self’s,
and want 3 to 5 thousand$ to do it, LOL.
I just did a map with 5 GCPs and 5 Check points, waiting on the results, small map prolly 3 acres
To clarify, the checkpoints are reported on the map processing report just as the GCPs are. Our checkpoints are in CAD instead of DroneDeploy as that is where we do our grading work and verification against surveyed data so we don’t use the checkpoint process in DroneDeploy too often.
In our area Surveyors will certify data from drone mapping if you provide them with the correct documentation. This includes a checkpoint report with the coordinate file and a proper level loop from the control that the GCPs came off of. Depending on the purpose it may or may not require them to do field checks and the cost is dependent upon the size of the site, but it is rarely more than $1,000. The only times we use this process are for certain municipal surveys and subgrade verification for roads and lots in subdivisions. The rest of the time our information is accepted by the Engineer by which a Surveyor never gets involved. We also provide Drone Services externally and occasionally do topographic maps for the Surveyors, but it is more likely that we are doing it for the Engineer and verifying the Surveyor’s information. Not because we are trying to prove they “were” wrong, but that the site still exists as they said it did and everything matches per the datum that we are provided to work from.
Sure, I understand. I was explaining how they are used. The “mechanics” are how they fit into the workflow depending on the software.
For Jeffery, In Pix4d and Metashape you enter them the same as GCPs only designate as checkpoints. They then show up in the error report. I’m guessing DD is similar.
Metashape report showing no checkpoints on this job but they would be listed there if they were used.
Correct. I think I misunderstood what you meant by,
as that you have to compare coordinates when it has actually already done that. Just the same in DroneDeploy.
The little I’ve done for engineers, they have the surveyors set the control.
Yeah, I didn’t specify that the software actually does the comparison. But it could be done manually too, albeit more “coarsely”.
That can be true as well. The majority of the time we run off the control that is already available and if we do not have enough that has been provided to us then we request that they set more control. We are pretty strict on what that control has to cover as we also use GPS Machine Control, but in our scenario it is part of the job so the Engineer or Owner are paying for it. This is why I always recommend that people who want to drone map for the Survey and AEC industries request contact with the CAD/Survey people as soon as possible in the front-end on the project. Allot of times you can negotiate them setting GCP’s as well. I run the drone program the same way whether it is for Chasco or for a client.
In that latest project that I discussed a bit with you, the developer purchasing the property mid-grading was requesting the photogrammetry derived topography. So, they directed their engineering firm to set whatever control I wanted. The cost of that, plus my fee was still way less and much faster than setting the hundreds of points needed with terrestrial practice. I’m not sure the engineering firm would have went that route but in this case they didn’t get a vote.
No doubt! That’s the way it should be. An impartial 3rd-Party just providing data for them to use however they want. I get allot of questions about what credentials or licenses Drone Mappers need and I recommend that you don’t do anything other than provide data. They have people on their end with the licenses and certifications to make the calls.