Changes outside the cloud
The designer clouds the change that prompted the revision, but a dimension elsewhere has also moved. Comparing by eye, nobody notices until the joinery arrives on site and does not fit.
Revision overlay
Compare drawing revisions by laying one over the other
A new revision arrives with a cloud or two and a line in the revision table, and everyone is expected to trust that nothing else moved. Laying the old and the new revision over each other shows every line that changed, clouded or not. Fidrel does this in the browser for PDF drawings and images: what exists only in the older revision turns red, what exists only in the newer one turns blue, and everything unchanged stays grey.
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Why changes slip through between revisions
Valuing the wrong difference
A quantity surveyor has to price what changed between the tender drawings and the construction issue. Without an overlay that means flicking between two PDFs and hoping nothing was missed.
No time to check every sheet
A revised set of thirty sheets lands late on a Friday. Most sheets have not changed at all, but nobody can say which without opening every one of them.
How the overlay works
Fidrel draws both revisions at one scale and looks at every point of the sheet. Dark ink found only in the older revision is shown red, as taken away; ink found only in the newer one is blue, as added; ink present in both is grey, and the paper stays white. The pages are lined up by their top left corner, as sheets of one drawing series normally are, and the file uploaded first counts as the older. The legend names both files, Only in the older and Only in the newer, so there is no doubt which colour belongs to which.
Documents, drawings & models
Any two PDFs, not only revisions of one drawing
The overlay works on any two PDFs, or any two images, open side by side, so it can just as well lay the architect’s plan over the services layout of the same floor. Pages are compared in order, the first with the first, the second with the second; where one file has fewer pages, the missing page counts as blank, which makes an added or removed sheet obvious.
Comparing two revisions in Fidrel
Step 1
Open both revisions
Open the current revision in the viewer, and the earlier one from the drawing’s Versions tab or from the register’s All revisions view, so that both sit as tabs in the viewer.
Step 2
Show them side by side
Choose Show side by side, or press S, and pick the other revision under File on the right. The two revisions now sit next to each other in the same window.
Step 3
Lay one over the other
When both files are PDFs, or both are images, an Overlay button appears above the file on the right. Press it and Fidrel draws both at the same scale and colours the differences.
Step 4
Step through the pages
Move through the set with Previous page and Next page. A page where nothing changed says No differences on this page, and Side by side takes you back to the two files.
Where an overlay earns its place
Use it before pricing a revision, before accepting it, and whenever a recipient asks what changed since the issue they hold. With the register’s All revisions view it turns that question into a few clicks rather than an afternoon with two printouts and a highlighter. Changes worth recording can then be clouded in a review and, if they need a formal answer, raised as an RFI from the markup.
What the overlay does not do
DWG drawings cannot be overlaid, and neither can a PDF against an image: both files must be PDFs or both pictures. The overlay compares ink, not meaning: it does not list the changes, measure them or name the dimension that moved, and it is not saved as a report. Pale colour fills and light tints count as paper, so a change shown only in a light shade may not appear. Sheets are aligned by their top left corner, so a revision whose drawing has shifted on the sheet shows as changed almost everywhere.
Related solutions
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Revision overlay
Frequently asked questions
Anything else on your mind? We are happy to help.
Talk to usYes. Open both in the viewer side by side and press Overlay. What is only in the older file shows red, what is only in the newer shows blue, and what is in both stays grey.
No. It needs two PDFs or two images. A DWG can be viewed in Fidrel, but to compare two revisions of it, use PDF prints of the sheets from the drawing software.
The file uploaded earlier. The legend under the overlay names both files, so you can check that the colours are the right way round before drawing conclusions.
Step through the pages: every page without differences says No differences on this page, so the sheets that did change stand out quickly.
No. The overlay runs in the browser on files already in the project, for anyone who can open both revisions, and it needs no separate comparison program.
Yes. Show side by side places them next to each other, and the overlay has a Side by side button to return to that view at any time.