What you see on the dump1090 local map is information based on several messages collected over time.
Modesfiltered works in a different way. It was a design decision to report flights as early and as consistent as possible. Even though a message doesnâ€™t contain altitude the flight will be reported based on the first message received. The report of the flight is delayed for up to 60 seconds to receive call sign and squawk. During this time altitude and receive time are not updated. When 60 s are over, the report is sent. If a flight was reported, it is banned for half an hour.
Regarding the logged format errors, dump1090 sent type 3 messages without position and type 7 without altitude. These messages are ignored although they may contain useful information.
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