# Uniting a set of triangles

In contrast to the previous operation this one allows to unite at once many triangles if they have adjacent edges.

To union several triangles:

1. Display a mesh or a submesh in the 3D viewer.

2. In the Modification menu select the Union of triangles item or click button in the toolbar. The following dialog box will appear:

- The main list shall contain the triangles which will be united. You can click on an triangle in the 3D viewer and it will be highlighted. After that click the Add button and the ID of this triangle will be added to the list. To remove a selected element or elements from the list click the Remove button. The Sort button allows to sort the list of IDs. The Set filter button allows to apply a definite filter to selection of triangles.

- Apply to all radio button allows to modify the orientation of all triangles of the currently displayed mesh or submesh.

- Select from set of fields allows to choose a submesh or an existing group whose triangle elements will be automatically added to the list.

3. Click the Apply or OK button to confirm the operation.

If some selected triangle elements have no adjacent edges with one of the others, the operation on these elements shall take no effect.