Vol

Command line: Vol

Description: Calculate volume for 3D models

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Using this command you can calculate volume that forms between a 3D model and a plan of constant elevation Z or volume that forms between two 3D models.

To calculate volume you can select 3D model from above or a plan of elevation Z that represents the above surface of the body for which volume is calculated and a 3d model from below or a plan of elevation Z that represents the surface from below (the reference from which positive and negative volume is calculated). Rule for the way in which positive and negative volume forms is simple: he part above the reference surface is positive and the part below this surface is negative no matter if the reference surface is a plan of constant elevation or a 3D surface (see figures below).

Besides positive and negative volume there are also calculated plan and surface area (slope area) that corresponds to bodies that form these volumes. To understand what sloping area is let’s take an example as area for a mountain covered with a thin layer of snow. The thin layer of snow is sloping area. In case of volume calculation between two 3D surfaces there are calculated sloping areas for the above and below parts for positive and negative volume.

Contour in plan can be limited with a polyline with condition that this to be inside 3D model or, in case of selecting two 3D models, inside both 3D models. If this polyline is not introduced then calculation will be made accordingly to limit given by 3D model or, in case of selecting two 3D models, accordingly to limit obtained through plan intersection of the two limits. Contour polylines can also contain arcs. For contour can also be selected a circle. There are also accepted 3D models that have holes (missing 3D faces).

Volume is calculate as a sum of 3D bodies (wedges) that are obtained from spatial intersections between 3D model and plan of constant elevation or through spatial intersections between two 3D models. Calculation method is geometrical. There are not used approximation methods and that is why it is recommended that 3D models you use to be as faithful as possible to the field.

3D bodies (wedges) can be drawn or not. Choosing to draw them or not can be done using command Om3d.

Volumes can be viewed or not. Choosing this setting can be done using command Om3d.

Ed surfaces can have any form, with triangles or grid. There are accepted any kind of three-dimensional entities excepting those closed in space (sphere) or those that contain holes in surfaces (cave). When you have such surfaces where 3D faces are overlapped you can calculate volume by splitting surface in several pieces.

When you use a smooth grid entity of type “Polygon Mesh” as 3D model it is recommended that the number of vertexes at interpolation to be big enough so that the surface to be represented correctly. Before smoothing this kind of surface choose density on the two directions using AutoCAD variables SURFU and SURFV.

Before calculating a volume it is recommended to view 3D model(s) using command VM3D.

Legend:

S1	-	plan of constant elevation or above 3D surface
S2	-	plan of constant elevation or below 3D surface (reference surface)
V(+)	-	positive volume (situated above reference surface)
V(–)	-	negative volume (situated below reference surface)
Ap(+)	-	plan area for positive volume
Ap(–)	-	plan area for negative volume
As(+)	-	surface area (slope area) for positive volume
As(–)	-	surface area (slope area) for negative volume
Asu(+)	-	surface area up for positive volume
Asd(+)	-	surface area down for positive volume
Asu(–)	-	surface area up for negative volume
Asd(–)	-	surface area down for negative volume

Fig. 1 – Case up surface and down reference plan

Fig. 2 – Case up plan and down reference surface

Fig. 3 – Case up surface and down surface (reference)