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Author Topic: GCP Error Explanation  (Read 2798 times)

chelseablanton

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GCP Error Explanation
« on: November 16, 2018, 10:26:18 PM »
Hello all,

I'm a new Agisoft user and I'm trying to evaluate my GCP error. I'm using DSMs and orthomosaics to analyze offset features along the southern San Andreas fault. I have read that acceptable pixel error values are below 1 (which my values are), but I have not found any acceptable values for the meter error. I first used all my GCPs and then used only 5 and the rest as check points (files attached).

Also, does the meter error represent global error? I would appreciate any assistance.

Best,
Chelsea 

wizprod

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Re: GCP Error Explanation
« Reply #1 on: November 18, 2018, 10:16:30 AM »
How were they collected?

chelseablanton

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Re: GCP Error Explanation
« Reply #2 on: November 19, 2018, 09:15:12 PM »
They were collected with an Emlid Reach RTK GPS. However, I believe the way I set up my base station the global accuracy of the base position is only about 2 meters.

Best,
Chelsea

Packy_GIS

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Re: GCP Error Explanation
« Reply #3 on: November 20, 2018, 11:01:38 AM »
If the base station has 2 m accuracy than you can not expect the GCP error to be low :) I do RTK measurements with 2-5cm accuracy and my GCP errors are (after point cloud optimalization) abour 5cm.
Packy
« Last Edit: November 20, 2018, 11:07:28 AM by Packy_GIS »

wizprod

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Re: GCP Error Explanation
« Reply #4 on: November 23, 2018, 08:37:02 AM »
They were collected with an Emlid Reach RTK GPS. However, I believe the way I set up my base station the global accuracy of the base position is only about 2 meters.

Best,
Chelsea

Hm, it should be down to 2-5 mm’s... I own a couple of Reach units (RS+) as well, and they are extremely precise.
Maybe your GCP’s were disturbed? Your rover pole not leveled completely?
Do you have some pictures of the environments your captured the points in?

wizprod

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Re: GCP Error Explanation
« Reply #5 on: November 23, 2018, 08:39:22 AM »
If the base station has 2 m accuracy than you can not expect the GCP error to be low :) I do RTK measurements with 2-5cm accuracy and my GCP errors are (after point cloud optimalization) abour 5cm.
Packy

The absolute coordinates of the base will not affect the relative accuracy of the rover. So you could have a base offset by many meters, and still have a relative accaracy of a very few millimeters. They are as such unrelated.