How to reverse engineer a schematic from a circuit board

Step 5 Circle the ground plane holes

When it is used in the centre-line mode, Autotrace turns pcb track pads into little loops.  It is necessary, therefore, to remove them.  Since we are going to delete the ground planes, some way of identifying where they are connected is necessary, so putting circles around them seems to be the way.  There is a simple manual way to do this.

Create a new brush.  Do this by creating a new image (File > New > height 64 width 64 > advanced options > fill with transparency).

Elipse tool (toolbox top row second icon) and set it's aspect ratio to fixed 1:1.

Draw a circle in the new image so it fill the box exactly.

Shrink the circle by about 5 pixels (Select > shrink)

Stroke the circle (edit > stroke selection) - use a line of 7 or 8 pixels

Save the file with the .gbr extension, in (for Linux users) ~/.gimp-2.6/brushes (the default export settings are fine).

It's worth doing a "+" and "x" brush whilst doing this - see next step.

Restart the gimp.

Now open the file you are working on, and create a new transparent layer.  Ensure you are working on this layer, and use your new brush (you will need to scale it) to dot a circle around every hole which is plated through the ground plane.  Multiple or really awkward holes, you can draw a rectangle or free selection around, and stroke selection as you did to create the brush.  Try not to overlap the edges.

Copy the alignment marks to the layer, turn off the visibility of everything except the circles you drew, save, and save a copy to a new .png file.