mapping 5000 new tree markers

[agengineer]

What are suggestions for how to mark 5000 trees on the ground so that they are highly visible for a aerial map?
The scenario is to plant fruit trees on sloping terrain that will be first marked on the ground with a crew of 3 ppl measuring correct spacing. The problem is the 18" tall flags are not visible via drone even at 100 ft. The actual 4x5 inch plastic folds and is "tiny" from the sky. So far, best solution i came up with is to paint a circle or x on each one. Then the problem is the paint doesn't last long.
Example of flags: 4” x 5” Stake Wire Marking Flags
Is there a better flag or marker around the same price? ($0.08 per flag plus marking paint) (call it $500 for 5000 marked trees)
Even better, an economical drone that would apply the flag/paint automatically either in a grid or in a row (spacing of 15'x20').
Thank you! Much appreciate any ideas.

 

[MA2 317]

Just a thought...

Maybe get a handful of larger flags such as bicycle flags and place them in a grid of sorts so that you know how many little flags you have in a given grid?

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[Meta4]

What are suggestions for how to mark 5000 trees on the ground so that they are highly visible for a aerial map?
The scenario is to plant fruit trees on sloping terrain that will be first marked on the ground with a crew of 3 ppl measuring correct spacing. The problem is the 18" tall flags are not visible via drone even at 100 ft. The actual 4x5 inch plastic folds and is "tiny" from the sky. So far, best solution i came up with is to paint a circle or x on each one. Then the problem is the paint doesn't last long.

For mapping missions, I use ground control points marked by pegged cardboard squares nearly 3 ft across and they are almost too small to see clearly at normal mapping heights.
You've got no chance using little flags.
Setting out 5000 markers of an appropriate size isn't going to be simple or cheap.
You might have to rethink the mission.
Do you really need to mark each tree?

 

[Tiger64]

What about large X with spray can . Would be cheaper than flags and easier to see from air.

 

[Howard70]

We had a similar project many years ago when we needed a way to distribute equally distant points across an island - the goal being to get the minimum number of points such that no place on the island would be more than x feet distant from a point. Turns out the distribution is not a square nor rectangular grid, but rather the vertices of triangles (sorry for the digression). Eventually we settled on producing a digital map with those “equi-distant” points plotted, determining the lat/long coordinates of each point, loading those into handheld gps units, and then letting those handheld units guide the field crews to place the dispersed items across the island. Basically the reverse of your approach.

In our case it saved a lot of time as measuring the positions on the ground across rough terrain would have been really slow. Later in the project we ramped up to much larger islands and used helicopters to disperse the items across thousands of acres.

Once you determine the required precision of placement (must a tree’s position be accurate to inches, feet, yards, or tenths of miles) you can determine the type of gps to use. If you need precision measured in yards you can use inexpensive “run of the mill” gps. If you need precision measured in inches you’ll need differentially corrected gps. Differential gps can be a more complicated process so you’d want to do further research in that case.

Howard