[rrd-users] rrd graph - multiple graphs on one plot?

Rob Conway rjconway at bigpond.com
Wed Oct 3 23:32:16 CEST 2007

Yes you can have multiple scales...however rrdtool cannot provide the scale.    If you normalise the data so it all fits on a single y axis, i.e. normalise everything to 0-100 %, all you then need to do is superimpose a scale onto the rrdtrend.  DO NOT LET rrd  print the scale just the trend area.   it is quite easy once you create a small picture (png) having the scale.

Imagemagick enables you to combine two .png files together and is a command line editor/tool for data manipulation under linux or I think windows.  I run it under a SLUG and linux ubuntu.  Thus you could make a complex multiscale axis and you just use imagemagick to combine the rrd graph and scale.  

The image below is just the rrdgraph combined with a scale to show alarm setpoint etc however theres nothing stopping you creating an alternative scale. 

This is the scale file, image magic updates this with actual data then overlays the completed scale onto the trend...and in firefox it shows its transparency

I use image magic to update the header on the web page below that shows real time data above the trend areas

RRDTool and imagemagick and you have all the required tools to create a really nice html interface for you data

Imagemagic runs under linux and the NSLU2 slug ....

rob, Australia

  ----- Original Message ----- 
  From: Gregory Guthrie 
  To: rrd-users at lists.oetiker.ch 
  Sent: Thursday, October 04, 2007 6:08 AM
  Subject: [rrd-users] rrd graph - multiple graphs on one plot?

  I wanted to have multiple data on one graph, and also add an 
  additional set of y-axis labels.

  I'd like to have wind speed and direction on one graph, and have the 
  velocity labels as standard on the left Y-axis, but also add a 
  direction indicator (N S E W) scale label over the scaled 
  (0-360  =>  20-30) wind direction on the right hand side of the graph.

  A site with a similar thing is at: 
  http:/ / www.iwindsurf.com/windandwhere.iws?regionID=100&siteID=1399
  but they use icons for direction, I wanted to just plot it as a graph.


  Gregory Guthrie

  MUM Faculty Mail - FM 1068
  Fairfield, IA 52557

  Dr. Gregory Guthrie 
           guthrie at mum.edu      (641)472-1125      Fax: -1103 
          Professor and Dean
          Computer Science Department 
          College of Computer Science and Mathematics
          Maharishi University of Management 


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