Gerber Compare

You can graphically compare old and new Gerber files for a project using Altium 365’s Gerber Compare feature. This capability is beneficial when PCB designers need to confirm changes in Gerber files before fabrication (e.g., unintentional changes). When the board layout is complex or large, but the changes are small, it can be very time-consuming to identify all the differences without a comparison tool.

Tip: You can compare two Gerber files by selecting any release in Project History. This can be accessed through Releases or Project History.

Access through Releases: Select Releases on the left side of the screen, and choose one release from the list. Click the three dots in the upper right-hand corner of the selected release, and select:

Compare Gerber to >> Fabrication A.x

Fig. 1 - Accessing Gerber Compare through Releases — **Fig. 1** - Accessing Gerber Compare through *Releases*

Access through Project History: Select History on the left side of the screen, and choose one project already released from the list. Click the three dots in the upper right-hand corner of the project and select:

History >> … >> Compare >> Gerber to >> Previous (Fabrication A.x)
History >> … >> Compare >> Gerber to >> Select Release
History >> … >> Compare >> Gerber to >> Files (This option allows the comparison of other generated Gerber files in Altium Designer that have been uploaded to Altium 365 Personal Space).

Fig. 2 - Accessing Gerber Compare through Project History — **Fig. 2** - Accessing Gerber Compare through Project History

You will receive an email when performing the first run of schematic comparison; it might take some time (30 seconds or more, depending on the board's size). Consecutive runs of the same dataset are instantaneous as the data are cached. When you see this screen, you can choose to wait for the process to complete or close the page:

Fig. 3 - “Comparison in progress” screen — **Fig. 3** -“Comparison in progress” screen

The email will be sent out as soon as the process is complete. After that, you can access the comparison by clicking the “Open in Altium 365” link:

Fig. 4 - Email from Altium’s notifications service, as received by the supplied user email, informing the user that the process is complete. — **Fig. 4** - Email from Altium’s notifications service, as received by the supplied user email, informing the user that the process is complete.

Once the comparison set has been selected, the results are presented in the Gerber Compare view in a new browser tab.

TIP: Color coding distinguishes between older Gerber data (red) and newer Gerber data (green). Switch between tabs to view the Gerber data for either of the compared sets (Fabrication A.x); the view switches to standard Gerber viewing mode, keeping the location and zoom level.

Fig. 5 - The different views of Gerber Compare — **Fig. 5** - The different views of Gerber Compare

The Differences panel on the left-hand side displays a view of the following sections’ details:

The identification of each layer
The quantity of layers
The differences in each layer
The x-y position of the selected group of differences

Fig. 6 - Details of the Differences panel — **Fig. 6** - Details of the Differences panel

Changes organized in groups with explicit identification on the screen correspond to areas of the board that change. Changes are displayed per layer. Clicking on a group will show a compare view that highlights any differences between the two revisions. As you can see, each group has a number, which is the number of differences.

Fig. 7 - Groups of changes — **Fig. 7** - Groups of changes

You can quickly switch between different layers and revisions on the side panel (see Fig. 6 - Details of the Differences panel). The location and zoom settings are preserved.

TIP: Gerber Compare performs a layer to layer comparison; detected differences are color coded and organized into groups.

Fig. 8 - The Compare tab — **Fig. 8** - The Compare tab

TIP: Areas that have not been modified are gray. Red indicates the changes in the previous revision of the Gerber file.

Move the mouse over the Compare tab to show the number of group differences.

Each detected group of differences is numbered and outlined. Click on an entry in the left-hand pane to focus on that specific difference in the main viewing area.

Select a layer and click on the group number zooms into the corresponding board area.

Fig. 9 - Cross-probing — **Fig. 9** - Cross-probing

TIP: If you zoom in to a group and change the tab to the older or newer Gerber file, the zoom level is maintained.

To measure the distance between two points, select the measure icon on the top right corner to measure and display the distance between any two points in the current document.

Fig. 10 - Measurement tool — **Fig. 10** - Measurement tool

You can also change measurement units by clicking the information icon switching between mil and mm.

TIP: The Distance Measurement tool reports the point-to-point distance, the X (horizontal) distance, and the Y (vertical) distance in both metric (mm) and imperial (mil) units. The Measurements panel provides quick access to these measurements. Its primary function is to help you compute the exact measurements to use in the PCB manufacturing process.

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