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Author Topic: Agisoft model accuracy  (Read 3341 times)

napdynamite

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Agisoft model accuracy
« on: July 19, 2017, 07:56:42 PM »
Hi,

I am flying 3DR solo with GoPro customized lens (no fisheye, 85deg HFOV). The calculated GSD is 4.05cm/pixels (@ 400 feet). The area covered was 65 acres with 4 GCPs (total station).
Following was the workflow I have followed to get final results:

1. Align Images --- Generic, High Quality.
2. Placing Marker Points and editing coordinates.
3. Optimize cameras.
4. Dense Point Cloud --- Medium, Aggressive.
5. DEM from dense cloud.
6. Orthomosaic --- DEM surface.


The final DEM was 18cm/pixels and Orthomosaic was 4.25cm pixels. I know that agisoft averages out the GSD because the aircraft never flies at exact altitude due to corrections it makes in autonomous mode. After cross checking the points with total station, I got an error of 4cm in X-Y which is not bad at all but in elevation I was getting 30cm error which is not good.
One thing I had in mind to correct this issue is to fly lower ( @100 feet) with a lower GSD (1.05cm/pixel). I want to know what is a typical horizontal and vertical accuracy Agisoft calculates and under what conditions do they depend?


Regards.

SAV

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Re: Agisoft model accuracy
« Reply #1 on: July 24, 2017, 09:39:40 AM »
Hi napdynamite,

As a rule of thumb you can expect a horizontal (X/Y) accuracy of 1-3 x GSD and a vertical accuracy of 2-4 x GSD when using highly accurate ground control points.
In your case the X/Y accuracy is OK, but the Z accuracy is too high. Depending on the complexity of the terrain/surface this could be due to insufficient image overlap.

Note: It is beneficial to collect a few more GCPs. Agisoft recommends 10-15. From my experience you should use at least 7 - 10 (which allows you to use a few as check points instead of control points).

Cheers
SAV

oscar_

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Re: Agisoft model accuracy
« Reply #2 on: February 15, 2021, 05:43:17 AM »
Hi napdynamite,

As a rule of thumb you can expect a horizontal (X/Y) accuracy of 1-3 x GSD and a vertical accuracy of 2-4 x GSD when using highly accurate ground control points.
In your case the X/Y accuracy is OK, but the Z accuracy is too high. Depending on the complexity of the terrain/surface this could be due to insufficient image overlap.

Note: It is beneficial to collect a few more GCPs. Agisoft recommends 10-15. From my experience you should use at least 7 - 10 (which allows you to use a few as check points instead of control points).

Cheers
SAV

Hello SAV,

Is that the official accuracy claimed by Agisoft (horizontal (X/Y) accuracy of 1-3 x GSD and a vertical accuracy of 2-4 x GSD)? Where is it documented?

Thank you,

Oscar