[rrd-users] Re: "Smoothing" a graph

Andres Kroonmaa andre at online.ee
Sat Feb 10 01:07:29 MET 2001


 I've just tried to implement a "moving average" with graph, and it
 seems to work pretty nicely. I got the idea from how cisco is doing
 average load calculations http://www.cisco.com/warp/public/66/3.html

 This allows you to smooth spikes on graphs, fill in gaps in missing
 data, and add a "trend" lines to your graphs.
 By playing with weight factor you can nearly any "smoothness" desired.

 (hope I just didn't reinvent a wheel ;)

 new-mavg = ( (last-mavg - datasample) * weight + datasample

rrdtool graph $png -a PNG \
  -h 400 \
  -w 1000 \
  --alt-y-grid  \
  --base 1000 \
  -s -7week     \
  DEF:max=$rrdfile:ds1:MAX     \
  CDEF:inp2=max,UN,1,max,IF      \
  CDEF:mavg=PREV,UN,inp2,PREV,IF,inp2,-,$weight,*,inp2,+      \
  "LINE1:inp2#FF0000:Max values\n"       \
  "LINE3:mavg#0000FF:Moving average, weight $weight"

>     From: Phil Henningsen <PhilH at astrology.com> 
>   I have an RRDatabase that saves five ABSOLUTE variables (MIN, MAX & 
>   AVERAGE) with readings taken at 5 minute intervals.  Two of the variables 
>   are "sparse and bunched".  For example, the 6 readings over 30 minutes 
>   might look like: 0, 10, 0, 12, 2, 8.
>   This causes the "two day" chart (where the horizontal grid lines are 1 hour 
>   apart) to look like a seismograph during an earthquake.  That is, the lines 
>   are very jagged over a wide range.
>   Is there any way, while graphing, that I can use an average "as if" it were 
>   sampled over a longer interval, thereby smoothing the graph?  That is, in 
>   the example above, the total over 30 minutes is 32, and I would like the 
>   graph to treat it as if each of the 6 readings were 5.333 or at a rate of 
>   1.0666 per minute.
>   If I look at a two day interval way back in history, say 6 months ago, the 
>   charts have the "smoothed" effect that I would like to achieve in the 
>   current period.
>   Thanks for your assistance.

 Andres Kroonmaa <andre at online.ee>
 Delfi Online
 Tel: 6501 731, Fax: 6501 708
 Pärnu mnt. 158, Tallinn,
 11317 Estonia

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