Help! Different measuring outputs of one mapping (two flights)


#1

Hello. I’m quite new here in the boards and just to get used to the DroneDeploy trial period, i’ve decided to move to forums and ask for professionals help.

I’ve done an aerial surveying with my Mavic Pro. I decided to do two mapping flights on the same area, just with a slightly different pre-flight settings (mainly altitude and flight direction)

  1. Flight - 44 meters of altitude, 19 degrees flight direction, Frontlap 75% / Sidelap 70%.
  2. Flight - 50 meters of altitude, 52 degrees flight direction, Frontlap 76% / Sidelap 76%.

Now while measuring the stockpiles i get small differences in the stockpile volumes. Why is that ocurring and which flight of these two i should trust in this case?

Greetings from Estonia.
Kaspar


#2

Welcome @Kasparov. How much variation are you seeing? Normally I would trust the higher one with more overlap.


#3

Well, not that much but just curious, since i also test DD for a client’s project.

The mapping consist total of 24 stockpiles measurements. While the total variation is 129 m3 between the two models, the average is 5 m3 / per stockpile. The biggest is 42 m3 and the smallest is 0.29. I guess it’s nothing, but just not sure which one of this makes more sense. The accuracy analytics app says the both are perfectly stitched and aligned and therefore gives no errors for quality.

I’m also a bit confused on the Linear and Lowest point measurement. Not sure which one would be correct for a stockpile that has one side slightly against very low wall, other than that it is completely on flat ground. Linear measure gives me a result of 178.9 m3, while lowest point gives me 198.9 m3. It is a stockpile which amount is known for customer, so they take it as a “verification test” for our project. So, i really want it to be accurate, but having a 10% variation between these two types of measurement functions, i don’t really want to let it slip in the final presentation. :confused:

Thanks in advance, i appreciate your help.


#4

From my experience error is between 2 and 5%. I’m assuming you didn’t use gcps? I normally don’t use gcps on stockpiles because we don’t need to be absolutely accurate. We’re just using it as a general guideline of what materials we have spanned across all job sites. This gives us a better look at how to share materials and how to reduce trucking. If you’re looking to get absolutely accurate then you may want to think about setting a couple of gcps. As long as they are easily visible four or five should be plenty.
As far as which type of base plane to use, your scenario of the stockpile being up against a wall or another stockpile is the only instance I would ever use lowest point. 99% of the time I used triangulated. The trick to using triangulated is carefully picking where you are setting your points and don’t use too many so that you get a smooth stitch across. If you want to use it in the situation like the wall then just don’t put any points on the stockpile as you cut across.