Enhancement: Trend lines to graphs

[xkilian]

Ability to display a trend line based on the displayed data. This would be done by the client-side rendering library as Graphite does not support this.

[Dieterbe]

i'm actually planning to something more generic to address specific use cases:

• trending (default): by default consolidated over a few pixels to have a smooth graph, irrespective of timeframe.
  this depends on support consolidation for raw/json/csv output graphite-project/graphite-web#153 ; provide an interactive slider to adjust consolidation interval, so you can make your graph more smooth or spikey
• spike detection (make sure all spikes are visible, no matter how short)

[dbishop]

Re: server-side consolidation of data for client-side graphing, this was our solution (but we never got around to polishing it for pushing back upstream): https://github.com/swiftstack/graphite-web/commit/c0a1a433a923a8e6432fe8629a9797c5c776bdad

(That same branch has a number of other graphite webapp scalability improvements we needed as well.)

[Dieterbe]

the new avg over <timespec> addresses this partially i think,
a moving average over a long timeframe is something else than a trend line (and I would have to dive into my old math courses to familiarize myself again with the uses/pros/cons of each)

but, I think practically speaking they accomplish pretty much the same thing, and you can use the movingAverage (avg over <timespec>) to see the trend, right?

see the docs on how to use:
https://github.com/vimeo/graph-explorer/wiki/GEQL#avg-over-timespec