Error build ArduCopter in elcipse

[GoogleCodeExporter]

What steps will reproduce the problem?
1.I follow this website
  http://dev.ardupilot.com/wiki/building-the-code/building-with-eclipse/
2.And when I did:
Select your project in the Project Explorer (normally on the left side of the 
window) and click the hammer button in the toolbar.
3.A error came out.

What is the expected output? What do you see instead?
The output is:
error ERROR: cannot determine sketchbook location - please specify on the 
commandline with SKETCHBOOK=<path>

What version of the product are you using? On what operating system?
I use a Version: Juno Release eclipse. And the project what I built is a normal 
ArduCopter from Ardupilot.
I use windows system to build it.

Please provide any additional information below.
I hope someone can help me out.This problem I cannot solve for a few days.

Original issue reported on code.google.com by zhujim...@gmail.com on 12 Mar 2015 at 3:40