=head2 More reading
-If you have difficulties with the way I try to explain them please read
+If you have difficulties with the way I try to explain it please read
Steve Rader's L<rpntutorial>. It may help you understand how this all works.
=head1 What are CDEFs ?
=head2 Degrees Celcius vs. Degrees Fahrenheit
- rrdtool graph demo.gif --title="Demo Graph" \
+ rrdtool graph demo.png --title="Demo Graph" \
DEF:cel=demo.rrd:exhaust:AVERAGE \
CDEF:far=cel,32,-,0.55555,* \
LINE2:cel#00a000:"D. Celsius" \
=head2 Changing unknown into zero
- rrdtool graph demo.gif --title="Demo Graph" \
+ rrdtool graph demo.png --title="Demo Graph" \
DEF:idat1=interface1.rrd:ds0:AVERAGE \
DEF:idat2=interface2.rrd:ds0:AVERAGE \
DEF:odat1=interface1.rrd:ds1:AVERAGE \
way: what you need is the "wipeout" variable and place a negative
sign before it: "CDEF:wipeout2=wipeout,-1,*"
+=head2 Filtering data
+
+You may do some complex data filtering:
+
+ MEDIAN FILTER: filters shot noise
+
+ DEF:var=database.rrd:traffic:AVERAGE
+ CDEF:prev1=PREV(var)
+ CDEF:prev2=PREV(prev1)
+ CDEF:prev3=PREV(prev2)
+ CDEF:median=prev1,prev2,prev3,+,+,3,/
+ LINE3:median#000077:filtered
+ LINE1:prev2#007700:'raw data'
+
+
+ DERIVATE:
+
+ DEF:var=database.rrd:traffic:AVERAGE
+ CDEF:prev1=PREV(var)
+ CDEF:time=TIME
+ CDEF:prevtime=PREV(time)
+ CDEF:derivate=var,prev1,-,time,prevtime,-,/
+ LINE3:derivate#000077:derivate
+ LINE1:var#007700:'raw data'
+
=head1 Out of ideas for now
This document was created from questions asked by either myself or