The goal of this wiki is to help users understand and interpret their graphs.
How are the graphs made?
The following are the tools used to create the graphs presented by the portal.
- collectd - a system statistics collection daemon
- rrdtool - A high performance data logging and graphing system for time series data
Where is the configuration file located for the graphs?
The configuration file is in fact one in the same as the script that is executed in order to create the various graphs displayed by the portal.
/home/pi/adsb-receiver/build/portal/graphs/make-collectd-graphs.sh
ADS-B Graphs
A breakdown of the current ADS-B and systems related graphs is as follows.
ADS-B Message Rate
Messages Received
Your SDR is receiving ADS-B messages that are 112 bits in length. There is a trade-off between taking more messages per aircraft in a defined time frame or having more aircraft seen but less frequent updates. The blue lines represent the number of messages per second your SDR → dump1090/978 decoded, as an average of the sample time frame.
Min/Max
I believe this is where most people would get confused when looking at this graph. When collectd creates the graphs, using the rrd data located at /var/lib/collectd/rrd/ it graphs the lines as an average of all samples. So, there are plenty of data points that are not graphed on a line. A yellow filled area represented, during that time frame, the minimum and maximum messages per second that was received.
7 Day Average
The average of the last seven days of messages received from your receiver.
Messages > -3dBFS/Hr (RHS)
The count of messages received that had a strong signal. dBFS is decibels relative to full scale. So, if you have a dBFS of 0 then you have attained the maximum that your device can handle. With cables, etc you will never hit 0 dBFS.
Positions/Hr (RHS)
How many of the messages received had position reports, or, using MLAT able to get a position.
ADS-B Aircraft Seen / Tracked
Aircraft Seen / Tracked
The number of aircraft that were seen that may or may not have position reports.
W/ Positions
Aircraft reported with positions
W/o Positions
Aircraft reported without positions
mlat
Aircraft reports that were MLAT only.
ADS-B Tracks Seen
The number of ADS-B reports of messages, that pertain to a single aircraft. If there was only one message then it is denoted in red.
ADS-B Max Range
The maximum range of which your receiver was able to pick up an aircraft. The red line is the maximum distance your receiver could pick up an aircraft in the defined time frame.
ADS-B Signal Level
Mean Level
The mean level of signal strength. The higher the number, the better (i.e. -20 is better than -23.2 in this example).
Peak Level
The best signal strength you were able to attain during that defined period of time graphed. The closer to 0 that number is, the better.
Noise
Wikipedia defines noise as a general term for unwanted (and, in general, unknown) modifications that a signal may suffer during capture, storage, transmission, processing, or conversion.
ADS-B Message Rate
Messages Received
Your SDR is receiving ADS-B messages that are 112 bits in length. There is a trade-off between taking more messages per aircraft in a defined time frame or having more aircraft seen but less frequent updates.
Messages > -3dBFS/Hr (RHS)
The count of messages received that had a strong signal. dBFS is decibels relative to full scale. So, if you have a dBFS of 0 then you have attained the maximum that your device can handle. With cables, etc you will never hit 0 dBFS, but -3 dBFS is a good benchmark to try and hit (i.e. with a filter).
Positions/Hr (RHS)
How many of the messages received had position reports, or, using MLAT able to get a position.
ADS-B Message Rate / Aircraft
Messages / Aircraft
The average number of messages received by an aircraft, during that period. =SUM(Messages)/SUM(Aircraft)
Aircraft Seen / Tracked
The number of aircraft seen or tracked by your ADS-B receiver.
ADS-B CPU Utilization
USB
How much of the CPU usage is attributed to the SDR that plugs into the USB port of your Raspberry Pi.
Other
Other uses of CPU beyond that of the USB and demodulator.
Demodulator
dump1090 and dump978 are both demodulators. So, essentially, how much of the CPU usage was attributed to dump1090/dump978.