Hi Donald, the indenting of this message is realy confusing, so I may be responding to the wrong thing here ...
Today O'Neil, Donald A. wrote: [...] > > Excel automatically graphs whatever size you want the graph to be, and > anti-aliases/scales things appropriately. I don't know how it does it, > just that if I graph the data in Excel it looks MUCH different than in > RRDtool... > > The main point is that the MAX and MIN values in the raw data do NOT > match the calculated MAX and MIN values on the graph. It appears as > though RRDTool calc's these max/mins from its own 'squished' data. > > I think the issue here is how RRDtool interprets so many data points to > create a graph that is only 500 pixels wide. I would think rather than > averaging the data it should take the absolute value of the max as the > point it plots, rather than taking an average of a number of points and > plotting it. I would bet this is how Excel does it. when rrdtool has to 'squish' 10 points into 1 it uses whatever consolidation function has been active for generating the 10 points (see the DEF line) to come to the 1 point ... in newer rrd version (1.2 and up) you can override this default with the reduce option in the DEF line. Lets say you have 3 Points: 10, 4, 1 If the 3 points are from an AVERAGE DEF rrdtool would draw the pixle at 10+5+1 / 3 = 5 If the 3 points are from a MAX DEF then the pixel would go to 10 If they were from MIN 1 Using the reduce option you can even have RRDtool show you MIN, MAX and AVERAGE from an AVERAGE DEF. I rest my case ... cheers tobi -- Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland http://it.oetiker.ch [email protected] ++41 62 775 9902 / sb: -9900 _______________________________________________ rrd-users mailing list [email protected] https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
