Digital Workshop

I am trying to illustrate geological features such as watercourse flows and contamination pathways.
I have an opening picture of a village scene which I to fold away to reveal the sub-strata and features like wells or septic systems. I can use "roll" animation to fold away the village image but I cannot see how to roll in the sub-strata image.
I like the roll effect around the mid point and it would be great if the rate of roll was a sine function so it looked as if a card was being rotated about a horizontal mid point.

David welcome to the forum and Opus fun. And thanks for creating/showing a Profile!

Try this. Just do it as a quick build test.
If you have 3 or 4 images (.jpg or .png to start with) and you have them scaled and aligned properly to make overlays -- it is easy.

Create a MultiFrame object. It will come with one Frame as a child object.
In the Organize tree, click to select the MF.
Right-click and select 'Insert Frame at End' (or at Start)
....
now when working in the Editor with multiframes, only the topmost child Frame will show (initially) in the workspace. Simply select other Frames in the TREE to give it focus and work with it. (there are other ways... but that's another day).

Select one of the child Frames and open its Properties dialogue. (Ctrl +r also works). Go to the 'Image' Tab and apply whatever map or illustration you want.
**Alternative method: rather than place the image as a Frame's background image, I prefer most times to do this:
Insert an Image Object in the child Frame. Size it and position it as needed. Use the properties dialogue to bring in the image file you want. Note 'Fixed', 'Scale', etc.

Tip: If you hold down the Ctrl key while dragging the image object's 'handle' to resize it, you can make the image extend beyond the Frame's area. But only the area inside the Frame will show at runtime.

Repeat to add images to the other child Frames.

You're almost done.
To control display of the different frames in a multi-frame, there are many options... I think you wanted:
Create 1 Button. Create an action... first create the Trigger: MouseOver.
Then create the Action.... category in the action list is 'MultiFrames'... simply select the Go To a Frame action. Click 'Apply' or 'Okay'

Now select that first Button (in workspace or in Tree). And duplicate it 2 or 3 times.
Edit or Change each button's actions -- you want to modify the go-to-frame action to point to a different Frame number.

As for your roll "animation", let me suggest an alternative:
You can apply this to the child Frame (or to the Image Object if you inserted that separate obj).
Select the child Frame. Modify its Properties. Go to the 'Transitions' Tab.
I would start with the 'On Hide' condition -- and look in 'more....' for all the transitions to your hearts whims.
(if your Pub is going to ever get complex, you will want to pay attention to the 'exclusive' checkbox option)

Anyway.... those are the pieces and the steps to get you started.

Do look into the Basic Helpfiles on the topics under MultiFrame.
-- you see the 'display order'
-- various options for navigating them, or autoplay the set, etc.

Given your project and area of interest, did you "Browse the Sample Publications"?
That is in Opus Editor under the File menu.
When you have some extra time, look at two Pubs there: Filter Effects, and Maps & Plans