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Author Topic: What is the ideal number of soil control points in an area of km²?  (Read 827 times)

IvamG

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Hi all,

I would like to create a very accurate DEM from aerial photos. I have a question regarding the number of ground control points. I would say more GCPs would lead to a more accurate DEM. Am I right?

From the Agisoft Photoscan manual:

In case of aerial photography and demand to fulfil georeferencing task, even spread of ground control
points (GCPs) (at least 10 across the area to be reconstructed) is required to achieve results of highest
quality, both in terms of the geometrical precision and georeferencing accuracy. Yet, Agisoft PhotoScan
is able to complete the reconstruction and georeferencing tasks without GCPs, too.

I am curious about the number of GCPs people use and how large the reconstructed area is? I would like to get a number of GCPs needed per squared (kilo)metre for example.

Leonardo

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Re: What is the ideal number of soil control points in an area of km²?
« Reply #1 on: July 16, 2018, 05:54:27 PM »
Hello, IvamG,
Normally, three GCPs are enough for georeference because three points can control a plane in 3d space. But for higher accuracy, more GCPs are needed in least square estimation.

Leonardo

stihl

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Re: What is the ideal number of soil control points in an area of km²?
« Reply #2 on: July 16, 2018, 06:17:08 PM »
You'll want to place the GCPs on the corner of the project site. From emperical testing I can see that a gcp has a usable radius of around 200m.