Check Points Verification Workflow

#1

When you guys do a scan and include GCPs and Checkpoints in the parcel, after processing, how are you comparing the coordinates of the check points against their surveyed values?

As simple as zooming in to the shot in QGIS, Global Mapper, or other software and reading the coordinates or ?

#2

The GCP’s are what they are and typically match, but the important factor is to shoot in a couple of checkpoints with whatever survey gear at the midpoint in between a couple of the GCP’s because the further you get away from the GCP’s the worse the error is. This is greatly reduced by using PPK or RTK which is why I use both the augmented GPS and GCP’s to get very tight. The improved GPS (as they claim with the P4RTK) doesn’t need GCP’s - maybe a couple of checkpoints for verification, but I don’t buy the fact that it is going to get inside of my tolerances for absolute accuracy. Yes their relative accuracy is good, but you end up basing it off of one benchmark that hopefully is in the middle of the project. I have greatly reduced my use of GCP’s (about half) and will continue to do so in efforts to make sure that my data aligns exactly with the CAD files with no manipulation when I bring it in. I will say though that my jobs that do not really require GCP’s have greatly benefited from the PPK alone.

#3

Hi Michael, yeah, re-read my question please. During point cloud processing, you specify GCPs but not check points. After the process, how do you “look” at the coordinates of the check points is my question.

#4

Understood. I check everything in CAD. I can check them in Precision 3D, but I primarily use that to create my DTM and it is just easier for me in CAD because that is how we create all of our points for survey. I like having the control over my DTM because I have found every other piece of software I have used a little lacking in their default DTM settings. I can set it and if I don’t like it undo and run the filter a different way. This workflow also allows me to check points in undisturbed areas and stake the surface the next time I hit that project.

#5

To bring features from the point cloud into CAD software, don’t you need to create vector features. And if so, do you just zoom in and set a point over the check point target?

#6

Not necessarily. Civil 3D can read point clouds, but I prefer to create a TIN file from the point cloud DTM. Once I have the TIN I can analyze it against the design or a previous flight. The checkpoints are obviously in areas that will not be changed by the DTM process so the point I shoot in should match that same YXZ that is in the surface.

#7

Gotcha. Are you creating the surface in Civil 3d or Carlson p3d or something else?

#8

Normally in Carlson Precision 3D because it was designed for point clouds of laser scanners back in the day and it is way faster. Since then they have tweaked it for drones and their survey mindset added several functions that I can’t do anywhere else.

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