How to overlay intersection with original object in Inkscape?


Say I'd like to produce the following diagram in Inkscape.

additive color diagram (RGB)

How were I to proceed? I can create three overlapping circles and I can create intersection objects from them but the problem is to align the intersection objects with the original circles. When I copy the three circles and paste them again, they turn up anywhere on the page and not in their original spot. It's very hard and in fact practically impossible to exactly realign the four intersection objects because even the slightest mismatch will create something like color fringing.

Edit: This is what I actually need and what I got so far with manual placement:

Big Euler Diagram

To be honest, the upper right intersection element is only darker than the other two because somehow I didn't get it to be bright. Maybe it's because of the gradients in the circles or maybe just because I don't have a very good mental model of what the overlays do.

11/16/2012 9:17:00 AM

Accepted Answer

An alternative approach would be to create the three circles as separate layers. Position the layers so they intersect as required and use blending mode 'Screen'. This will give you the color mixing that you show in your example. To make the background black you can fill the remainder of the page of create another layer, fill it with black and move it to the bottom of the stack.

There is another method to create the intersecting areas that will be more suited to your drawing.

  1. Shift select the three circles.
  2. Ctrl-D to duplicate the circles (they will appear right on top).
  3. Shift select two circles at a time and do Path -> Intersection. This is display the intersection area between the two circles. Select whatever color you like.

In your case you'll need to repeat step 2 thrice, since you need to get three, 2-circle intersection areas. To get the intersection area at the center, shift select the three 2-circle intersections you just created, Ctrl-D, then Path -> Intersection.

11/30/2012 1:51:00 AM

Very late to this party, but if anybody else needs to know how to paste an object on the original place where it was cut from you can just use Paste in Front (Cmd+Shift+F). That would make it easier to perform these boolean operations on shapes.