Scatter plot visualization for screen resolution stats #1560

The current charts (pie,bar) aren't quite applicable to get an overview about the visitors screen resolutions.

• Like the current browser stats, there are too many values and only the greatest 4 are displayed. This can lead to huge misinterpretation of the data, since there might be many different screen sizes
• Even if the bar chart would display all values at once, there is the problem of how to sort the values the right way.

The obvsious reason is that pie and bar charts are made for simple, one-dimensional data sets but the number of visits per screen resolution is a perfect two-dimensional data set. In fact, the screen resolution values consists of two parts: the screen width and the screen height.

One of the best and simplest visualization type to display two-dimensional data sets is the scatter plot. You can see the difference in no time by looking at the attached prototype. In my opinion, this is the only way to make the screen resolution stats usable.

I got the scatter plot running with OFC, but there are several improvements needed:

• the php wrapper class for scatter plots is very poor, compared to the wrapper classes for more common chart types. I had to built part of the json-data by hand to get tooltips working etc.
• I don't really understand how OFC places labels on the axis, so I inserted the labels in the prototype by hand. OFC only put one label on each axis. Also it seems that OFC ignores the set_step() method for the y-axis
• to be honest: I have no clue how to hack another chart type in the data table visualization template. Since now I simply avoided any contact to this mystical class
• The base wrapper class for OFC charts (Piwik_Visualization_Chart) does only support one-dimensional data sets (I will create a seperate ticket for this issue)
  Keywords: interesting

Attachment:
res-scatter-plot.png

probably too much work for only one report.

There's a bug(?) in OFC where set_range($min, $max) will undo a previous set_step($step) -- the workaround is to call set_range($min, $max, $step), or call set_step() after set_range().

I'd like to see this in core. Should be easier after we merge Gall's Scatter Visualization code into core and libs.