# Comparison of GM 3D Model Results vs. Calculated Values

Hi GM'ers.

A client recently asked me how accurate the results were from Global Mapper 3D models? They use expensive mining software (\$\$\$) and I guess there was some question over how reliable GM model results were.

So I created a model of a truncated cone (i.e. a 100 m deep "dummy" Pit with 45 degree side-slopes, 100 m radius pit floor and 200 m radius pit crest) and exported the Volume Calculation results directly from GM as shown on attached worksheet (N.B. elevation grid and earthworks sample spacing at 0.1mx0.1m).

You can see that GM modelled results compare favourably with values calculated from first principles with GM values about 0.1% to 0.5% greater in this case, depending on the parameter considered.

It should also be noted that the “3D Area” output from GM includes the “pit floor” area, so to get the inclined pit wall area its simply a matter of subtracting the pit floor area from the 3D Area given by GM. Simple!

Anyhow, thought I'd pass this along in case its helpful to others...

Cheers,

Alistair.

• Hi Al,

Long time no chat!

These are the results using the 'expensive mining software' Deswik.CAD if it helps in any way (see spreadsheet).

Note that Deswik.CAD generates a 48-sided wireframe from the imported circles I created with AutoCAD. With that in mind, the volume of the Deswik.CAD frustrum cone is 7,311,105.29 for reference. So, the Deswik.CAD error is +0.26% overall compared to your frustrum calculator results.

I used to use Global Mapper for volume calcs but quite frankly the process was very tedious when trying to calculate the storage volumes for facilities that do not have a flat surface e.g. Tailings Dam, Dry Stack or Waste Rock Dump. It works fine when calculating simple ponds though.

I recall discussing the issues with you and sharing my convoluted workflow using Global Mapper, a common reference plane and Excel to subtract the volumes. I think the volumes were reasonable with Global Mapper but Deswik.CAD always ended up with the precise volumes that I got with Civil 3D.

Cheers,

Steve

• Thanks for the info Steve!

Working as a "one-man-band" the main difference for me is that GM costs about 2% of what Surpac costs (I'm not sure how much Deswik costs, but I'm sure its not cheap?) and so GM is affordable for me.

At the end of the day, in mining the <0.5% difference in landform volumes is insignificant compared to bulking factors that miners use to convert from bcm to lcm! 😉

Cheers,

/al