The correct way to do it would see if its possible to get a reports analysis from lets say DART then take an API feed from it and bring that into piwik. Piwik tracks page views and referrers etc but DART does CTR rates (since it serves ads) What ad serving system are you using?
I am working on this project as well. There are two API calls in the ad server which generate piwik analytics, one for ad impressions, and one for ad clicks. A custom variable is used to distinguish click and impression analytic visits. My current issues are:
Calculating a custom dataset of CTR for the piwik graph module. WIth impressions and clicks, I can filter by the custom variable and the graph automatically counts the results. For CTR I need extra calculation besides the standard count of a filtered recordset.
Displaying multiple custom data lines for impressions, clicks and CTR on the same graph.
Another idea I had was querying the archive_blob tables directly and building the graph in jqplot, however I would like to check first the piwik does not already have this capability built.
ok my thought was actually pulling an api of a finished calculated report from the actual ad server.
DART or OPENX allow CTR reports as i understand it so my thought was to see if an API of the finished calculated results was possible.
Instead of it being n the same graph what if you had 3 reportlets in a dashboard (and excuse my naivetee) but
1 for ad impressions
2 for ad click
3 a custom variable based on a calculation of 1 and 2 (If piwik allows any sort of custom API variable manipulation this way I dont honestly know, but a custom calcuated metric perhaps?)
Sounds like you both are 90% there Im afraid its beyond my reach to help. Hope I may have given another user an idea to solve it worst case this would be an incredibly powerful feature were it possible when leveraged against GA or Omniture.
This is quite an advanced question that would require much thinking so i’m afraid I can’t help, but everything is possible for sure, by building a new plugin to extend the VisitsSummary graph for example. Please contact: http://piwik.org/consulting/ if you 'd like to Piwik experts to help!