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Ground Control Points, how many is too many?

Hello,

So the situation is roughly 13-15 acres of photographed area, 90% coverage using a grid and the area is for the most part square and virtually no ground features like hills or levees.

How many ground control points is about what you think would be necessary?

A colleague recommends constructing about 50-60 of 2’x2’ and 2’x3’ ground control points and I think we could get by with maybe 10?

Would appreciate any feedback and if this is the wrong place for this post please let me know.

I just don’t think the correction we will get having more than 15 is worth the construction time.  Would like to see some work done on this, maybe error versus number of ground control points per acre? Might even be interested in doing that research myself since I’ll be having so many of them.

Hi SCOOT,

It is hard to give an estimation of how many GCPs should be used in a specific project.

A minimum number of 3 GCPs is needed, but we recommend between 5-10, well-distributed over the area , depending on the terrain, the difficulty of the area, the height differences and the type of projects. If you find any of these the cases mentioned before, we advise you to increase the number of GCPs.

For more information about the GCPs please check here: https://support.pix4d.com/hc/en-us/articles/202557489 

I would also recommend checking the Do more GCPs equal more accurate drone maps? which contains some concrete example. 

Best,