# Volume to a Base Level

This option computes the volume of the area under the triangles to a nominated base level,
the results are in cubic metres.

The program will search the triangles file and display the highest and lowest levels on the surface.
It will then prompt the user to enter a base level, the default will be the minimum level on the surface.

Press the 'Compute' button to start the calculation, the results are displayed in the edit box on the screen.
If a listing file is selected, the results will also be written to the listing file.

Volume Calculation: The program will then process each triangle in the job and compute the surface area of the
triangle and the average height of the triangle from the base level.
The volume for each triangular prism is then computed as the Area x Height.
Each triangle is computed in turn, keeping track of the 'cut' and 'fill' volumes.
The results are printed as two volumes, The 'fill' is above the base level, the 'cut' is below the base level.

If a triangle crosses the base level the program will compute a net cut or fill volume,
this may lead to inaccuracies in the volume. It is better to choose a base level below all points.

**Points to note: **

- Models require same Surface Area and same Base Level;
- GeoSurvey Base Level defaults to the lowest triangulated RL;

## Process

- Inspect data, triangulate model, contour at 0.1m and resolve any errors.
- Review triangles and ensure there are no ‘holes’ (shade triangles).
- Topo>>Volume to Base Level. Pick an RL that is just below the lowest point in both
triangulation models. Run the volume computation for both your models.
- Subtract one volume from the other to provide the overall volume difference.
- Verify the Surface Area is equal in both models.
- Compare results. Check Nett Fill Vol against Base Level (Bulk Fill) results.

**If the Design boundary falls outside the NS model** then it can be adjusted provided the
NS data does actually cover the Design extent.

- Amend the Boundary as necessary in the NS and extract to a new file (copy/paste) with null heights as before.
- Open Design file, delete the old Boundary and append the new.
- Interpolate the new Boundary points in your Design file.
- Run points too close to resolve any duplicates – delete or average points, which ever is easier.
- Re-triangulate.

**If a model has insufficient survey points **

Create Mesh – if necessary. (Topo>>Irrigation>>Create Mesh). It aids triangulation and
provides a smoother model definition.