volume calculation accuracy

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dan machon
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Joined: Wed Sep 22, 2004 6:49 am
Location: british columbia, canada

volume calculation accuracy

Post by dan machon » Wed Sep 22, 2004 7:01 am

hi there i have a client asking me the accuracy of my volume calcs... i know it depends on many different factors such as number of points and break lines etc...using the old avg end area the accuracy is in the neighbourhood of 5-10 %....does this sound reasonable using mscad2004 ???? any help to get this guy an answer would be helpful...thank you

Glen Cameron
Posts: 1395
Joined: Fri Nov 08, 2002 12:18 pm
Location: Corbeil, Ontario, Canada


Post by Glen Cameron » Wed Sep 22, 2004 7:29 am

As you mentioned, there are many things that will have a factor on your volume calculations. The number of shots - the placments and spacing of the shots, breaklines, the spacing and layout of the shots on the 2 surfaces - where the pline is drawn for Area Volumes - etc.

In comparisons to other programs on the market, we seem to be within a percent or two to all of them.

So to quote a rough accuracy of 5% to 10% would not be a problem - but you of course have the ultimate responsibility to check your answer before you supply it to the client. Assuming that everything was collected in an optimum way and no significant errors were encountered, then your answer should be perfectly fine and should be in the range you mention - or maybe even less.

Glen W. Cameron, C.E.T.
City of North Bay, Ontario

Richard Sands


Post by Richard Sands » Wed Sep 22, 2004 2:12 pm

I responded to a similar Q a good while back (not sure if its still there). Beside the number of shots, whether break lines are run there is also the shape or perhaps more correctly the smoothness of the heap, hole or surface as well as the shear mass.
Other factors are the changes in volume from solid to loose and visa versa. I.e. the compaction ratios can vary with different materials and thus the volume. Do your clients expect loose or compacted volumes these may differ by 15+/- %. If the surface is pocked with irregularities are they prepared to smooth the surface, take care in how stuff is dumped or removed? If its extracted dry and measured dry and then it gets wet it may naturally compact and the volume is reduced.
Do you get to accurately measure the base (whats under/ above the surface before anything is removed or added). That can have a big factor on results if an even plane is assumed under a stockpile etc.
I always maintain that 10% is the minimum accuracy unless it’s a very smooth surface and well defined. (remember large even looking surfaces can be very deceptive as an imperceptible depression or hump may lead one to make assumptions and space the points out too far.) But I also state the volume is as measured in its condition of the day. It’s worth mentioning the compaction factor.
As a comparison I have ran the same figures through MSCAD and another surveying package and got identical results. There is nothing wrong with the theory of MSCAD that I can see.
I may have laboured here but I'm not sure what you are measuring nor the scale of it all. Hope this helps.

Jerry Johnson


Post by Jerry Johnson » Fri Sep 24, 2004 1:32 am


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