FlightAware Discussions

Stats Page Error? Distance from Feeder

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…

I don’t know if this is the same thing that I asked about in a different thread, to which I received no reply …

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.

Thanks for checking the data from your end!