As Andreas already replied to you:
"Unfortunately dropbox's public folder hosting functionality was disabled in the meantime.
Please find referred sources at https://s3-eu-west-1.amazonaws.com/wikitude-webapps/tmp-14days/clustering.zip
Note that the sources are quite outdated but the clustering.js may still help.
Hi, I'm having the same problem.
there is a lot of invalid links in those threads,
could not download clustering.js file.
Is there any solution?