Co-rendering Multiple Volumes
In any view, only one volume can be selected at a time. However, creating a volume group and adjusting each volume's class settings can provide a means of directly comparing overlapping volumes or volumes on the same 2D line (e.g. an array of angle stacks).
The order in which volumes are listed in a group define the display precedence. You can change the opacity of the overlying volume in order to see the underlying one, and in doing so providing a means of making visual comparisons of the data.
Creating a volume group
![Creating a volume group](https://media.screensteps.com/image_assets/assets/003/944/510/original/8ce8553e-2591-4413-b750-f96c7e7ab845.png)
- Right click on multiple volumes in the Volume tab.
- Click Groups > Add to group > New...
- Select the desired Group.
- Type a name for the group and click OK.
![](https://media.screensteps.com/image_assets/assets/003/944/512/original/1fbbc2ee-76f7-4e8f-a148-decb49649e5b.png)
Alternatively, a volume group can be created in the Group tab.
- From the Control Panel, open the Group tab.
- Click the blue "+" icon, select New Display Group and give the group a name.
- At Volume, click the blue "+" icon to add volume(s) to the group.
- Search and select the volumes you want to group.
- Arrange the order of the volumes by clicking and dragging the left side of the volume row. The order in which volumes are listed in a group define the display precedence.
Changing the class settings
![Changing the class settings](https://media.screensteps.com/image_assets/assets/003/944/515/original/b4ffa957-b066-4652-9f02-d88eab98301a.png)
Adjust the opacity and display settings of each volume's class to obtain a clear comparison view of overlapping volumes (see Overview of Classes and Colourbars).
Selecting a group in views
After creating a group, select the group in the Vol selector in the navigation bar of any section or 3D Views (see Viewing a Volume Group).
Tip: If your grouped volumes are not displaying in Gather Views, make sure they are on the same spatial grid (e.g. IL/CL and increment). Because gathers are not interpolated for display, grouped gather volumes will only display together at locations they have in common.