Volume Discrepancy

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plms
Posts: 4
Joined: Wed Mar 19, 2003 6:50 am

Volume Discrepancy

Post by plms » Mon Dec 01, 2003 11:00 am

When I perform an area volume calculation the quantities given vary depending on the order in which I enter the two surfaces I have created and computed. The difference is on the order of 4,500 cubic yards. Any explanation/advice? Thanks again.

Vincent Popish
Posts: 129
Joined: Thu Nov 14, 2002 11:24 am
Location: Grand Junction, CO

volume diff.

Post by Vincent Popish » Mon Dec 01, 2003 11:31 am

Do you have different exterior boundaries for the two surfaces? If you use one outside boundary for both surfaces it usally works better. Such as where the 2 files come together, or some area outside the changes between the 2 surfaces.

Also I have noticed if you redifine a surface, and click the clear surface button, it often doesn't clear the lines and points from the first surface. You need to rename the surface or exit and not save the surface to redifine a surface.

Hope it helps.
Vince Popish

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

Post by Glen Cameron » Mon Dec 01, 2003 11:35 am

Some things that may affect the volumes would be:
1) The number of points in each surface.
2) How the points are laid out on the surfaces.
3) Were breaklines used and how many points were from them compared to other points
4) Did you use a Planar Tin, Tgrid, Tin with derivatives, or a Grid when defining the surfaces to do volumes between?
5) Were the two surfaces the same size, shape and location in plan view?
6) Was the polyline, use to do the area volumes, laying completely on both surfaces, or did it stray off of either of them at any point?

There may be other considerations that may also give you some minor differences. If you would like me to examine your job, please feel free to email me at support@microsurvey.com

I would need the FLX, MSD and QSB files, if you would like me to look at the job.

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

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