Compute 2.5D Volume Report Questions

[asart]

Hey!

I'm sorry if I'm asking a dumb question and misunderstanding something fundamental, but I cannot understand some of the values from the volume computation tool.

I am currently trying to estimate earthworks volume between two sequential aerial scans.

I've been looking at the volume computation algorithm in the source and the help.
I believe I have a somewhat decent understanding of the algorithm, but I cannot understand why Volume is computed, essentially, as (Added volume - Removed volume).
Shouldn't the two be added as an absolute value in order to get a total volume?
Also, as a physical representation, how can I visualize what volume is, as it is currently output?

A sample output I have is:

Volume: -918.158
Surface: 972.500
----------------------
Added volume: (+)22.691
Removed volume: (-)940.849
----------------------
Matching cells: 58.9%
Non-matching cells:
ground = 0.0%
ceil = 41.1%
Average neighbors per cell: 7.5 / 8.0

Just a sidenote: I am aware that this is a bad cell matching count.

Essentially, with the framework of earthworks in mind, one could look at Added volume as Embankments and Removed volume as Excavations. What then would the purpose of the Volume field be, since it is not the combined volume of both?

Also when computing between the first scan and an arbitrary constant height, and a different scan and the same constant height, shouldn't the difference between the two Volume fields be the same as if I did the comparison between the two clouds?

I am sorry for the novel I've written instead of a post.

Thank you!

[daniel]

The total volume is indeed the difference between the 'added' and 'removed' volumes:

Code: Select all

22.691 + (-940.849) = 22.691 - 940.849 = -918.158

If you have a perfectly flat terrain. Then add X m^3 of dirt somewhere, and remove Y m^3 of dirt somewhere else, then the new volume of dirt will be the previous one, plus 'X - Y'.

People using this tool are generally not interested in summing the volume of 'air' inside the excavations, and the volume of dirt in embankments. If you are, then I guess you'll just have to do the computation manually...

[asart]

Thank you for the quick reply!

That is a fact, but my question then becomes:
If I have two perfectly flat terrains, which cross at a given angle, then the value of Volume added would be the same as the value of Volume removed.
In that case would the Volume be 0?

[daniel]

The volume 'difference' yes. Since this tool asks for a 'before' and an 'after'.

If you want to compare both to a common flat terrain at Z = 0 for instance, then you'll have to compute the difference between each cloud and the common reference. But that would probably be equivalent in the end to manually compute the sum of the absolute volumes. However, mind that you are summing 'air' and 'dirt'... which may not make sense depending on your application.

[asart]

Unfortunately that is precisely what I am after.
How would I then compute them by hand?
Are there tools I could use in CC to compute just the 'air' and 'dirt' separately?

Thank you for your patience!

[daniel]

Well, CloudCompare displays the added and removed volumes separately? So you just need to do the maths?

22.691 + 940.849 = 963.54

[asart]

Aha!
Thank you for answering simple questions.
So I'm safe in understanding that Added volume would be the Embankments and Removed volume would be the Excavations then.

[daniel]

Well, it depends on what the 'before' cloud (or altitude) is? If it's a flat terrain/plane, then yes.

[asart]

I see.

In that case if I calculate the volume of the before cloud and a constant height, and then the volume of the after cloud and the same constant height, shouldn't the difference between those two volumes be the same as if I calculated the total volume (i.e. the sum of 'dirt' and 'air') of the before and after cloud?
Sorry if that sounds a bit unclear.

So 'before' and a constant height of 69.83:

Volume: 560.248
Surface: 1,652.250
----------------------
Added volume: (+)715.705
Removed volume: (-)155.458
----------------------
Matching cells: 31.6%
Non-matching cells:
ground = 68.4%
ceil = 0.0%
Average neighbors per cell: 7.7 / 8.0

'After' and a constant height of 69.83:

Volume: 928.421
Surface: 779.250
----------------------
Added volume: (+)928.421
Removed volume: (-)0.000
----------------------
Matching cells: 15.1%
Non-matching cells:
ground = 84.9%
ceil = 0.0%
Average neighbors per cell: 7.3 / 8.0

And the before and after:

Volume: -1,172.158
Surface: 1,041.000
----------------------
Added volume: (+)27.766
Removed volume: (-)1,199.924
----------------------
Matching cells: 63.0%
Non-matching cells:
ground = 37.0%
ceil = 0.0%
Average neighbors per cell: 7.6 / 8.0

So if X = "715.705 + 155.458 = 871.163" and Y = "928.41", shouldn't Y - X equal a value in the computation between 'before' and 'after'?

[DA523]

vol.png (40.6 KiB) Viewed 7430 times

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ex.png (90.42 KiB) Viewed 7430 times

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