I have a question concerning calculating Volume with Manifold 8
I have a drawing representing building footprints.
I have a DSM surface component with Surface heights, and a DTM surface component with Terrain heights
Both surfaces have the same origin, pixel size, scale and projection.
I aim to calculate/evaluate the volume for each building.
So I have 2 approaches:
1.1 / With DSM and the building Drawing, use Surface Tools --> Transfer Height --> to a new field dsmHeight in building drawing
1.2 / With DTM and the building Drawing, use Surface Tools --> Transfer Height --> to a new field dtmHeight in building drawing
1.3 / With building Drawing and simple arithmetic calculate Volume1 = Area([Geom (I)]) * (dsmHeight - dtmHeight)
2.1 / With DSM and DTM using Surface Tools --> Transfer --> subtracting DTM from DSM surface --> creating a new resulting Surface renamed to Result
2.2 / With Result Surface and building Drawing calculate Volume2 = Volume([Result], [Geom (I)])
Findings : Volume1 and Volume2 are different.
I would expect both results Volume1 and Volume2 to be equal. The 1st approach on transferring the heights (dsmHeight and dtmHeight) to the building component uses the average surface height that lay within the building footprints.
With the 2nd approach (subtracting DTM from DSM,) the height in the final Result surface somehow must differ from the arithmatic (dsmHeight - dtmHeight) in the first approach.
How does this come ? I would like to understand and know which approach is the most accurate.
Thank you , in advance, to all the contributors on this forum for looking into this.