How to Select Circles by Radius Size for Halftone Image

Any assistance would be greatly appreciated!

Desire:

To create a half tone pattern from an image

Challenge:

To only output circles of .25" diameter

Process:

I began by modifying someone's file I found on the internet.

http://www.liftarchitects.com/blog/2010/11/8/surface-patterns-for-g...

They created a 3D file for CNC milling hence the panel descriptions that mention z-axis movement and etc. I only need a 2d output of circles.

I successfully input my own image into their file and created the halftone pattern. The problem is that the output pattern creates a circle for every point on the 1" grid and the pattern is created by varying the size of the circles. I have tried to modify the file to only draw circles of .125 radius but I could not figure it out.

Work Around:

The circles currently drawn would be fine if I could find a way to select ones of a certain size. If I could select all the circles of a radius between .05" and .125" I could then create a point at the center of each of the selected circles and redraw the circles with my desired .125 radius. I then tried modifying another file I found online to select circles of only a certain size.

http://www.grasshopper3d.com/forum/topics/select-circles

However I was unable to get it to work as the circles output in the halftone pattern have a wide range of radii. I could not figure out how to select the circles within the output range of radii.

Any suggestions would be a huge help!

Thanks

Zak