Distance Accuracy is off


#1

We are using the demo version to see if this is a product we can use. We have made several flights at several altitudes, and in on that, we did we had a surveyor go out and set up point to validate measurements. With one of the measurements, it was off by ten feet. Drone Deploy measured it at 1230 feet, and the surveyor measured it at 1220. Now that is less than one percent error, but I have to believe that it can do better. So, will it get better with upgrading to the business plan or will I have the same issues? Is there something I can do to increase accuracy? I am running a P3 advanced. The images are 4000x3000 and are jpeg. I would like to shoot raw but do not know if Dronedeploy would upload them. I am running iso at 100 and a shutter speed at 180 to 200 depending on the lighting. I also am using an ND8 filter on the camera. can someone help answer some of these questions


#2

I get the most accurate results with:
(1) missions flown on overcast days
(2) low wind of < 5 mph
(3) a manually set slow speed of 9 mph to ensure low blur in the direction of travel
(4) 80% front & side overlaps
(5) 300’ altitude above takeoff point for mapping trees 100’ tall on a slope that falls 100’ over a 1000’ distance putting tree tops 200’-300’ below drone
(6) Flying long E-W legs of 1200’ with short 70’ N-S legs at turns
(7) Manually reviewing all 200-typical photos for blur and removing these from the upload list. This results in the removal of the takeoff photo and then almost all photos at the 9 turns in the mission which can be up to 18 photos. I also look very closely at several photos to ensure there is minimum blur in the direction of travel.
(8) Using automatic camera settings
(9) Using a fully charged battery so the mission can be flown with no battery changes. At 9 mph it takes 19 minutes to fly the 27 acres of my missions. The battey charge is 30% at mission end.
(10) Using a DJI Phantom 4 Pro which takes JPEG photos.
(11) Flying beyond the boundaries of the area being mapped. For a 17 acres map the mission area is 27 acres as displayed in DroneDeploy. The actual flight path is 10’ beyond the long E-W sides and 50’ beyond the N & S ends. There is an additional area counted by DroneDeploy due to the camera field of view.

I do not have survey results for long distances. But for a few hundred feet I see less than 1 foot error on maps made from missions following the 11 steps above. This is for both horizontal and vertical errors.

Hope this helps.

Regards,
Terry.


#3

Did you use ground control?


#4

No. This costs more, Business Plan + $49/map. Not in my budget. But I do correct the large altitude error that is due to the P4P using a barometer for measuring altitude.

GCP’s can help a lot. But you need a budget for them.

Regards,
Terry.


#5

@Marksman681

This won’t help with your accuracy issue, but ditch the ND for mapping. It is slowing your shutter speed and introducing the potential for motion blur with no benefit. ND’s are for getting smoother VIDEO. They are NOT better for still imagery.


#6

What is ND? Does this have something to do with the camera?


#7

You must use ground control points to get better accuracy because of limitations of the drone’s GPS. Drone’s GPS coordinates are recorded with each photograph and are close enough to position photos so that software can stitch them together but they fall short for exact positioning relative to the ground. Using ground control utilizes an additional procedure in which the user locates ground control points (targets visible in the photographs) and assigns them coordinates established by ground surveying methods. This allows the software to apply corrections when stitching the photos so that the resulting map both fits together and is corrected for true position on the ground. With good ground control accuracy of a few inches is typical. Without it, errors of several feet or more are typical. Drones with survey grade gps onboard can also obtain good accuracy but are much more expensive and complicated to operate.

Hope this helps,

Steve


#8

@SolarBarn ND = Neutral Density filter. :wink:


#9

Dave,

Does my Phantom 4 Pro have a ND filter on its camera?

Regards,
Terry.


#10

Terry, No, the P4P has a clear lens protector only. You can get ND filters that will screw on in place of the protector but those are accessories. They can be useful when recording video. Search: why use nd on drone to find explanations why. In a nutshell, you use them to slow the shutter speed based upon lighting conditions and your chosen frame rate to record the most “pleasing” video.

They do have a purpose in still photography on the ground, like smoothing waterfalls. But in the air, and especially for mapping, we want the fastest shutter speed we can get with the available light. The absolute opposite of what an ND filter is designed to do.


#11

Everyone here does understand that the drone GPS is simply a recreational grade unit right? What you are asking is for an accuracy of less than the GPS receivers capabilities, not counting PDOP and other interference. Ground control can help, but that surveyor is using 10’s of thousands of dollars of high accuracy equipment, that 1K drone with a cheap GPS chip is never going to get that accurate. 10 feet in my experience is pretty normal.