## Volume Menu

The Volume menu has some optins for measuring the volume between a set of surface patches and a plane, or between two surface patches. It also contains some options for editing meshes by trimming to a plane or removing selected triangles.

### Interacting with the plane

For the plane to be visible "Display Plane" needs to be selected. This should show a plane with one side red and one side green. The plane position can be altered either interactively or by setting parameters directly. To set the parameters directly choose "Set plane" and you are presented with a dialog to set the translation and rotation (the rotation is applied first in the order z then y then x, apparently). The set the plane interactively select "Move plane" from the menu, shift+right click and drag will rotate the plane, ctrl+right click and drag will shift the plane.

For a mesh with a template that has been labelled with symmetric matched point information, it is also possible to estimate the symmetry plane from the points using the appropriate menu option.

### Area selection

It is possible to "paint" a number of triangles in order to use them for measuring areas and volumes. Choose "Select Area" from the menu and use Alt+right click and drag to choose triangles in the mesh for inclusion in various volume measurements. Note that for some of the area based measurements it is important to select the area on a warped "standard" mesh rather than on the original. This way the selected area can be mapped onto any other mesh with the same topology.

### Measurements

There are two types of volume measurements, measure the area from the surface to a plane by projecting along the plane normal direction and summing the volumes of the resulting polyhedra, or measuring the volume of the polyhedra formed between matching triangles between two meshes and summing the results. For the plane volume measurement any mesh can be used, but a selection on one surface may not necessarily map on to another surface (unless they are both warped versions of the same base mesh), for example for batch measurement. For surface to surface based volume measurements it is essential that both surfaces are warped versions of the same base mesh. Note that the volume is measured as the sum of the resulting polyhedra, so odd cases like intersecting surfaces may not give the kind of results you expect.

### Mesh editing

The plane or selected polygons can also be used for some simple mesh editing. Selected polygons can be deleted, or all points on one side (the red side) of the plane can be deleted.