Aircraft.json - How to determine the number of aircraft?

matthkarl · August 22, 2020, 4:45pm

I would like to fetch a few high level values from the aircraft.json from dump1090-fa/data/aircraft.json.

Getting the data and going through the values is not the problem. What is confusing me is that I have roughly 30% more records in “aircraft” than what the webpage under dump1090-fa is showing as “Total Aircraft”.

While the webpage tells me there are some 28 aircraft (including the list in the table below), I do get some 38 aircraft records in the .json. I have gone through the data and also looked at all the various fields in this description of the data: README-json.md · master · Sebastian Schumb / dump1090 · GitLab
But I can’t find the criteria as to when dump1090-fa is “counting” a record and when not. Is there a simple rule to that?

wiedehopf · August 22, 2020, 5:11pm

Well you could look at the javascript code.

Pretty sure it’s seen < 60 or something along those lines.

matthkarl · August 23, 2020, 6:00am

I have tried to figure out how that is done by looking at the javascript. But I’m not that fluent in javascript, and I couldn’t figure out where and how it is filtering the records.

wiedehopf · August 23, 2020, 7:42am

Why do you care anyhow?

I’m pretty sure about the (seen < 60) condition.
(seen < 30) or even less might be a better representation of the planes you’re currently receiving.

So it’s really up to your interpretation.

matthkarl · August 23, 2020, 11:36am

It’s not THAT important, but I was just wondering why certain aircraft are filtered out. So when I display the number of aircraft on my dashboard, I’d like to have the same value for consistency reasons.

wiedehopf · August 23, 2020, 1:39pm

github.com

flightaware/dump1090/blob/master/public_html/script.js#L1230


      
          
          
			})
          		});
              };
          
          
    var conversionFactor = 1000.0;
              if (DisplayUnits === "nautical") {
                  conversionFactor = 1852.0;
              } else if (DisplayUnits === "imperial") {
                  conversionFactor = 1609.0;
              }
          
          
    for (var i=0; i < SiteCirclesCount; ++i) {
          	    var distance = (SiteCirclesBaseDistance + (SiteCirclesInterval * i)) * conversionFactor;
                      var circle = make_geodesic_circle(SitePosition, distance, 360);
                      circle.transform('EPSG:4326', 'EPSG:3857');
                      var feature = new ol.Feature(circle);
                      feature.setStyle(circleStyle(distance));
                      StaticFeatures.push(feature);
                      SiteCircleFeatures.push(feature);
              }

58 seconds.

I’m somewhat familiar with the code after making a fork of the UI.

matthkarl · August 23, 2020, 2:45pm

Oh, that is seconds. I somehow assumed wrongly that was the number of aircraft.

Awesome. Thank you very much!! That made my day.

MarkMoerman · August 23, 2020, 5:23pm

An aircraft can remain in the JSON file for up to 300 seconds after it was last seen.

MarkMoerman · August 23, 2020, 10:10pm

In the JSON file, the seen_pos - how long ago (in seconds before “now”) the position was last updated, has a maximum value of 70 seconds.

system · August 23, 2021, 10:10pm

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Aircraft.json - How to determine the number of aircraft?

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