A Data Plotting Tool for QUASAR
Sam Kumar, Michael P Andersen, David E. Culler
Goal: To create a web-based visualization tool
for timeseries data that:
• can plot dense data streams without high
network latency, and
• provides information about the density of the
data as a function of time.
Approach: To plot a stream of data over a
specified time range, apply the following
procedure:
1. Divide the time range into small intervals,
each corresponding roughly to one pixel on
the graph’s current scale.
2. For each interval, query the archiver for a
statistical summary (min, mean, max) of the
data over the interval. Thanks to QUASAR’s
stratified multi-resolution design, this is
very efficient.
3. Plot the minimum, mean, and maximum
values of the data over the specified time
range. Linearly interpolate between adjacent
points, but not across gaps (for clarity).
4. In addition, plot the number of data points in
each interval above the graph to show how
the data density varies with time.
Zoom on the
scale of
weeks
Zoom on the
scale of hours
Zoom on the
scale of
milliseconds
The data density plot (above the
graph) and cursors (black lines)
placed by the user provide additional
quantitative information about the
displayed data. See the figure to the
right. ►
As the graph is zoomed
in or out, the amount of
time corresponding to
each pixel changes. The
width of the time
intervals changes to
maintain a one-to-one
correspondence with
pixels. Therefore, the
plotter continues to
display data at a
relevant resolution as
the user zooms in or
out. See the figure to
the left. ◄