# 3D Surface Area - results seem dodgy

Posts: 5
Hi, we are calculating a 3D surface area for a farmer and have used Global Mapper (using Cut & Fill Volume Measurement, base plane 0m) and a CAD package for comparison to get the undulating surface area. Global Mapper's CUT_AREA_3D came out about 9% higher than the ENCLOSED_AREA or planar area. The CAD package surface area had about 0.5% more surface area than planar area.

So I made a test dataset which we manually calculated the surface area for and Global Mapper's 3D Area came out far too high.

The test dataset is 5500m long by 1300m wide on the plane with the long edges 85m elevation and the valley contour line in the middle 10m. Therefore the actual width on the slopes is 1386m x 5500m which  gives 719ha and Global Mapper's CUT_AREA_3D found 734ha (GM planar area is correct). Now I am wondering if I misunderstand what GM is actually calculating?

All data is in Map Grid of Australia GDA94 Zone 50 (rough equivalent of UTM50 South).

Thanks
Jane

• Posts: 5
Edit: the test dataset surface area is 1308.6m x 5500m = 719ha <span></span>
• Posts: 106
I've also run a test on based on an Autodesk Civil 3D surface with precise values for comparison. Basically my result also show the results to be too large.

Test data:
2D Area = 164,178.168 sqm
3D Area = 167,085.854 sqm
Minimum z value = 200.34 m
Maximum z value = 221.41 m

Global Mapper results:
2D Area = 164,500 sqm
CUT_AREA_3D = 254,340 sqm (using a base of 0m)
CUT_AREA_3D = 267,900 sqm (using a base of 100m)

• Global Mapper Programmer Posts: 1,944
Hello,

I suggest that you contact Blue Marble Support directly via email (geohelp@bluemarblegeo.com). Please provide a detailed description of your workflow (including screen capture of the options you selected for calculating volumes) and data that can reproduce the issue. Thank you.

Cheers,
Bob
• Global Mapper User Posts: 117Trusted User
But please report back if you find a solution!