Selecting Visible Elements    

This task shows you how to hide already hidden elements when performing a selection, thus selecting only the visible elements in a subdivision surface.

Open the ModifySurface5.CATPart document.
The Show hidden lines in dashed lines option is selected in Tools > Options > Shape > Imagine & Shape > Display tab, Base Mesh area.

1. Click Modification in the Modification toolbar.

2. Select Subdivision Surface.1.
   You can see that the hidden edges and vertices of the mesh are also visible and can be selected. Selection of visible elements thus becomes difficult. In this case the View and Selection All mode has been clicked in the Operations toolbar.

3. Click View and Selection All in the Operations toolbar. The View and Selection All  icon state changes to View All and Selection Front .

   You can see that all the hidden (back) edges of the subdivision surface are grayed out and are not selectable.

4. Click View All and Selection Front in the Operations toolbar. The View All and Selection Front icon state now changes to View and Selection Front .
   You can see that all the hidden edges covered by the subdivision surface are no longer visible. Some part of these hidden edges which is not covered by the subdivision are still visible in the mesh, but they are grayed out and are not selectable.

    To go back to the initial state, click it again.

5. Rotate the subdivision surface or change its shape (in case of a modification). You can see that as the surface moves the relevant hidden edges are not visible. The selected edge remains highlighted and selectable even after rotation.

• The visualization of the three help text level icons can either be on the same icon cyclically or in an expandable separate toolbar. This depends on the option chosen in Tools > Options > Shape > Imagine & Shape > General tab, Command Options Menu Mode area.
• If Show hidden lines in dashed lines option is cleared, hidden lines are displayed with the same settings as the base mesh elements defined in Tools > Options > Shape > Imagine & Shape > Display tab, Base Mesh area. Depending on the different states of View and Selection mode command, the subdivision surface is as seen:

	View and Selection All
	View All and Selection Front
	View and Selection Front

• In some case, it may happen that some edges are seen though they are behind the face. This is because the surface has such faces with the normal directed towards you and not towards the back of the screen as it is in most of the cases.