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Project accuracy

 Hi,

According to experts, the project accuracy is 1.5 x GSD for 2D products and 2.5 x GSD for 3D products …

Assuming a 2.27 cm GSD, I think that a measurement performed on 2D products may present an error of approximately 3.40 cm and in 3D products this error would be approximately 5.7 cm, is this correct?

In this case, could the height measurement of a 40 cm plant vary from 34.3 cm to 45.7 cm?
 
Is this precision for mappings without GCPs?

With GCPs can I reduce this margin of error?

Thank you

Hey Walter,

Your x,y and z accuracy estimations seems pretty reasonable. If a plant height is 40 cm and your GSD is around 2 cm’s it could be anywhere between 34 and 46 cm’s. With GCP’s you would definitely be able to reduce the RMS error for x,y and z. I can’t speak for z too much but for x and y, you may be able to get sub-centimeter accuracy with GCP’s.

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Thank you Selim for your support

Hey Walter,

No worries, I am happy to help.

The values you listed are a general rule of thumb, and can actually be difficult to achieve at that.  They’re not necessarily a statement of accuracy, it’s really just a general value in terms of what to expect at best

The application you’re talking about is not a good one to try to hit that number. Vegetation & Crops is one of the hardest things to accurately reconstruct, and one of the common “tricks” to use on problem sites will further reduce your GSD.  For example, initial processing at 1/2 image size can help with reconstruction on something like a homogeneous corn field with a light breeze, but you’ll be reducing your GSD.  If you have the “Multiscale” option checked in processing settings, you’ll get a similar result. 

Not to say what you’re trying to do isn’t possible, but you’re basically trying to hit the best accuracies in the worst situation. 

Hey Derrick,

You are right it is pretty challenging to reconstruct vegetation and crops. Based on my experience however I believe it is pretty reasonable to get an accuracy of 5-8 cm’s for RGB’s with a GSD of  2-3 cm’s and an accuracy of around 10 cm’s for Multispectral with a GSD of 10 cm’s. I have had projects that had sub-centimeter accuracy, which is definitely not a requirement to get an accuracy that high.