Question.
When using the analyze volumes tool, the resulting quantity between two terrains should be the same as the quantity as a delta terrain built from the same surfaces and analyze volumes performed against a plane elevation 0.00'. But, it is not.
We have a project with the following results comparing existing to proposed (analyze volumes).
Cut Factor = 1.0000
Fill Factor = 1.0000
Cut = 6254773.6620 sf3
Fill = 4400699.4384 sf3
Balance = -1854074.2236 sf3 = 68,669.42 cy
We then generated a delta terrain between the same terrains, then used analyze volumes terrain to plane of 0.00 and had the following results.
Cut = 6255136.0495 sf3
Fill = 4405001.8043 sf3
Balance = -1850134.2452 sf3
We get the same result regardless of using boundaries. Could someone try to explain.
I would not expect exactly the same numbers. The analyze volume command analyses the prisms formed between the two triangular meshes, and the prisms are going to be different between the two originals and the delta/planar. Normally when I run a test like this, I find the major differences fall on the edges of the terrains in the places where the long, skinny triangles are calculated (slivers), but in this case, if every prism is different, the difference might be spread among the entire surface. In the numbers you give, there is a 0.0058% difference in the cut and 0.097% difference in the fill for a total of 0.04% difference on the site.
I've isolated it to the Terrain to Plane option of the analyze volumes. I clipped a portion of both existing and design to the same boundary. Then exported to several different applications to check earthwork volumes. All came back the same (within 1 ft3) except the Terrain to Plane in OpenRoads. So, then to make sure that's the issue, I made a Terrain of elevation 0.00' spots and ran the analyze volumes Terrain to Terrain using the elevation 0.00 surface and the delta terrain. It matched precisely the result of EX to FG.
fyi, applications checked earthwork volumes and resulting delta terrain to plane of 0.00. PIRSS4, Inroads SS2, Geopak SS2, Civil 3d 2019, Terramodel, Business Center. All agree with each other except SS4 Terrain to Plane.
Clipping to the same boundary is a good test as it can eliminate a lot of the edge triangle interference. Can you post the DGNs with the terrains that you used so we can test and log? https://bentley.sharefile.com/r-rdbdd279fd3e4469b