For some time I have noticed that on the statistics page, the reported distance of a plane from feeder does not correlate with what I see on the FA map plot … at least when “nm” is my chosen unit.
Today, my feeder was reporting a plane which was tracking tangentially just beyond the 120nm ring. I estimated its distance to be 125nm. However, in the “Recent flights with positions from this feeder on FlightAware.com” table, the distance was reported as quite a bit more than that.
I have also noted that when the same table reports a plane being reported by my feeder in say, the 120-160nm bin I sometimes don’t get credited with those positions in the “Positions Reported by Distance from Receiver” table and chart.
So using the lat/lon of my feeder and the lat/lon of the position report I calculated the distance and confirmed the discrepancy. The stats page seems to be reporting distance from feeder in statute miles because when I apply the 1.15 conversion factor all seems well with the world.
(While we are on the topic, the units “km” in the header of the “Nearby ADS-B sites” table should be removed.)
PS:
Anyone can confirm the anomaly by choosing statute miles as their units then checking distance of a plane from the receiver, then switching to nautical miles and checking that same distance. The distance reported does not change.
I’ll second that observation. In the " Positions Reported by Distance from Receiver" graph, its showing that I’ve received 32 positions from 250+mi, but the performance graphs from the receiver is reporting 257 statue miles for my max, but only 1 in the past 24hrs, everything else is under 250 statue miles.
Looking at where those reports would need to be on a map, and per what I’m seeing on www.heywhatsthat.com, getting anywhere near 250 statue miles should be very, very rare for me. If it were nautical, over 250 would be impossible for my location, so I’m pretty sure the ‘mi’ reported on the stats site is statue miles, so I’m wondering if a conversion is off somewhere?
The underlying bucket used for data collection on the server side is 200+ NM nope - looking at the code it really is 250 mi, and it’s the reverse conversion to NM that’s showing the wrong boundaries. Let me look at your data a bit more.
Stats appear to be correct. Here are the 32 positions reported that were >250 statute miles from your receiver during the 2020/02/17 UTC day:
clock 1581899019 hexid AA9F3F position {41.79881 -122.05380 7 371} 5 A alt 38000 5 A distance 252.4352930780986
clock 1581899046 hexid AA9F3F position {41.83342 -122.05268 7 371} 16 A alt 38000 0 U distance 250.07674231024814
clock 1581901319 hexid AABD2B position {41.72309 -122.19071 8 186} 0 A alt 40000 0 A distance 256.6790075702516
clock 1581901336 hexid AABD2B position {41.75792 -122.19397 8 186} 0 A alt 39975 0 A distance 254.26713828883663
clock 1581906364 hexid ABC4D8 position {41.79409 -122.14255 8 186} 3 A alt 38000 3 A distance 252.11894552786904
clock 1581908835 hexid AA6FCA position {41.74139 -122.27873 7 371} 11 A alt 40000 11 A distance 254.91282978365928
clock 1581908856 hexid AA6FCA position {41.80172 -122.28997 7 371} 1 A alt 40000 1 A distance 250.70233329190341
clock 1581914266 hexid AA4C3E position {41.77961 -122.26806 8 186} 0 A alt 37975 0 A distance 252.34204308979423
clock 1581914271 hexid AA4C3E position {41.78752 -122.26806 8 186} 1 A alt 37975 1 A distance 251.79807736896362
clock 1581914273 hexid AA4C3E position {41.79325 -122.26806 8 186} 0 A alt 37975 0 A distance 251.404037398507
clock 1581917982 hexid AD41CD position {41.82793 -122.11208 7 371} 11 A alt 40000 11 A distance 250.0114369293939
clock 1581920004 hexid A56E0D position {41.64825 -122.24756 7 371} 0 A alt 40000 0 A distance 261.48896914577045
clock 1581920038 hexid A56E0D position {41.69637 -122.25692 7 371} 8 A alt 40000 8 A distance 258.1280108607542
clock 1581920064 hexid A56E0D position {41.72831 -122.26314 7 371} 17 A alt 40000 1 U distance 255.89715793272484
clock 1581920068 hexid A56E0D position {41.76215 -122.26972 7 371} 3 A alt 40000 3 A distance 253.5336961190602
clock 1581920075 hexid A56E0D position {41.77472 -122.27215 7 371} 3 A alt 40000 3 A distance 252.65586756413225
clock 1581920094 hexid A56E0D position {41.80600 -122.27815 7 371} 6 A alt 39600 6 A distance 250.471704008722
clock 1581950847 hexid AB5F87 position {41.75731 -122.09573 8 186} 0 A alt 40000 0 A distance 254.96574495677342
clock 1581950855 hexid AB5F87 position {41.76997 -122.09718 8 186} 1 A alt 40000 1 A distance 254.08818092626007
clock 1581950857 hexid AB5F87 position {41.77487 -122.09774 8 186} 1 A alt 40000 1 A distance 253.7485353165687
clock 1581950867 hexid AB5F87 position {41.78828 -122.09930 8 186} 4 A alt 40000 4 A distance 252.81882752455408
clock 1581954454 hexid AB77EE position {41.82568 -122.03925 8 186} 0 A alt 38000 0 A distance 250.71044031896975
clock 1581957061 hexid A6AF5E position {41.78324 -122.08953 9 75} 5 A alt 39000 5 A distance 253.23457195429012
clock 1581957090 hexid A6AF5E position {41.72983 -122.06472 9 75} 6 A alt 39000 6 A distance 257.0732900071015
clock 1581957114 hexid A6AF5E position {41.70341 -122.05236 9 75} 17 A alt 39000 17 A distance 258.9735820903735
clock 1581957690 hexid AA7E3A position {41.81159 -122.12575 7 371} 0 A alt 38000 0 A distance 251.03468385578745
clock 1581960060 hexid ABD60B position {41.77931 -122.10205 8 186} 1 A alt 38000 1 A distance 253.413563170887
clock 1581960064 hexid ABD60B position {41.78566 -122.10167 8 186} 1 A alt 38000 1 A distance 252.9813012891418
clock 1581960072 hexid ABD60B position {41.79548 -122.10109 8 186} 4 A alt 38000 4 A distance 252.3128210492436
clock 1581960097 hexid ABD60B position {41.82820 -122.09912 8 186} 13 A alt 38000 13 A distance 250.0861653203993
clock 1581960269 hexid A35744 position {41.58197 -122.29887 8 186} 0 A alt 41075 0 A distance 265.7803793907549
clock 1581960288 hexid A35744 position {41.55185 -122.27964 8 186} 5 A alt 41075 5 A distance 267.9506702773489
Very, very interesting… So now I’m going to have to check with the data from my end somehow. I’m 99% sure those over 250 are just not possible given the setup I have, but maybe I’m lucky. But the performance graphs package is saying for the past 24hrs I’ve never reached over 257 statute miles. Hmm…
Looks like the performance graphs use of collectd/rrdtool is averaging the values in an interval. So if one report in a 1 minute ‘interval’ for plotting a value (looking at the 6hr graph) is at 257mi and there are a bunch at 100, the graph is showing the average of the reports so its no where near 257mi. Not sure yet why that is or how to work around it.
