Viewing, comparing, and marking up drawings
Comparing drawings with overlays
Overlay mode places one sheet on top of another. It works best for revisions or drawings that cover the same physical area.
Overlay mode places one sheet on top of another. It works best for revisions or drawings that cover the same physical area.
Best for: Coordinators and reviewers comparing aligned sheets on web or in the native app.
Start an overlay
Open the sheet or revision selector, find the comparison sheet, and choose the overlay action. You can also start an overlay from the revision selector. On phones and tablets, the sheet picker and overlay controls use compact layouts.
Overlay comparison is available in supported desktop and mobile browsers, including Safari on iOS, and in the native app. A smaller screen changes the control layout but not the purpose of the comparison.
Choose a comparison mode
- Differences uses contrasting colors to make changes easier to spot.
- Ghost makes one sheet faintly visible over the other.
- Highlight emphasizes areas that differ.
No single mode is best for every sheet. Differences is helpful for linework, Ghost is useful when you still need to read both drawings, and Highlight can make broader changes easier to scan.
For Differences and Ghost, use Blend Amount to change the balance between the two sheets. Reset the blend if the comparison becomes hard to interpret.
Align sheets with three points
If the sheets do not line up:
- Select Align Sheets.
- Choose three matching reference points on the first sheet.
- Choose the same three points on the second sheet.
- Review the aligned result.
Use reference points that are far apart and easy to identify, such as grid intersections or fixed building corners. Three points clustered in one small area can produce a poor alignment elsewhere.
During alignment, some comparison modes are unavailable. Complete or cancel alignment before closing the overlay.
A comparison is not a change record
Overlay mode helps you visually inspect differences, but it does not decide which changes are contractually important. Confirm findings against the issued documents and record decisions in an appropriate Topic, RFI, or other project workflow.