The Overlay feature allow an addendum drawing to overlay the Base image, making it easy to identify changes. Think of this like placing two drawings on top of one another and being able to see changes between the two. Although overlays can be assigned on the Cover Sheet (see Related articles) the instructions below are geared toward adding them using the "Add Overlay" option available in the Context Menu on the Image Window.

Overlay Rules, Restrictions, and Notes

• Only one overlay image can be associated with a single base page. If you have multiple addenda for the same page, the base page must be duplicated, and then each addendum overlaid on a copy of the original.
• An overlay cannot be an indexed (multi-page) file. Each overlay must be a single page file (an example of an indexed file is a single PDF file that contains multiple pages - in this case, only Page 1 can be displayed as an overlay. Use an external PDF viewer to extract the individual pages, if necessary). See Related Articles for details.
• When adding an overlay to a page on the Image Tab, the program automatically attempts to resize the overlay to match the base image. It is possible to adjust the overlay manually using the steps below to fine-tune the image.
• When you add an overlay on the Image Tab and adjust it, a copy of the overlay image is saved as a tiff in a folder named "Overlays" and all changes are saved to that tiff file. The Cover Sheet is updated to indicate the overlay file is the tiff (the original overlay file is not altered). Adding overlays directly on the Cover Sheet does not automatically create a tiff copy.
• Overlay images are always displayed in grey-scale, regardless of whether the image file is color.
• At high zoom levels, pixel-level differences are bound to occur - this is simply the nature of digital imagery. The Overlay function is designed to show you differences in the plan at reasonable zoom and highlights any changes, even a pixel difference, between the base and overlay images.
• Additions appear in BLUE (meaning something exists only on the overlay) and deletions appear in RED (meaning something exists only on the original (base) image)

Overlay toolbar

The Overlay Toolbar provides quick access to adding, resizing, deskewing, and removing overlay drawings, along with toggling current view.

By default, this toolbar is docked below the Image Toolbar, on the right side of the application.

Button Icon	Function	What it does/What it means...	Keyboard Shortcut
	Add Overlay	Opens a dialog box where you select which plan/image you want to overlay to the current Plan
	Resize Overlay	Launches the Resize Overlay wizard so you can resize the overlay to match the Base image/takeoff on the current page.	<Alt> + <R>
	Align Overlay	Allows you to fine-tune alignment between the overlay and base images
	Deskew Overlay	Just like deskewing a base image, allows you to correct for slightly skewed drawings (typically happens when paper plans are scanned)
	Remove Overlay	Removes the overlay from current page - you can then select/add a new overlay
	Toggle Base-Overlay-Both	Toggles the view between Base Image, Overlay, and Both. Button shading changes depending on which view is active: - Both; Base only; Overlay only;

The articles that follow walk you through selecting an overlay and then adjusting it, so it matches your base image.

Converting Image Files (Drawings) to TIFF Format

Selecting an Overlay Image