Valid targets being filtered out compared to dump1090 #24

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opened 2025-08-25 08:27:13 +02:00 by olemd · 1 comment

olemd commented

2025-08-25 08:27:13 +02:00

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Problem Description

SkyView is filtering out several valid targets that dump1090 is able to show. This suggests we may have overly strict filtering or decoding problems that are rejecting legitimate ADS-B messages.

Expected Behavior

SkyView should be able to decode and display all valid aircraft that dump1090 can successfully process and display.

Potential Root Causes

Decoding problems in the Mode S/ADS-B message parser
Overly strict validation in the beast protocol handler
CPR position decoding being too conservative
Message type filtering excluding valid aircraft
Signal strength thresholds being too high
Incomplete implementation of certain ADS-B message types

Investigation Areas

beast/parser.go: Raw message parsing and validation
modes/decoder.go: Mode S/ADS-B message decoding logic
modes/cpr.go: CPR position decoding and validation
merger/merger.go: Data fusion logic that might filter out sources
Message type handling for DF17, DF18, and other formats

Steps to Reproduce

Run dump1090 and SkyView simultaneously on the same data source
Compare the aircraft list between both applications
Identify aircraft visible in dump1090 but missing in SkyView
Analyze the raw messages for the missing aircraft

Impact

Missing valid targets reduces the effectiveness of SkyView for aircraft tracking and may cause users to miss important aircraft in their coverage area.

Debugging Approach

Enable verbose logging to see rejected messages
Compare raw message handling between SkyView and dump1090
Log validation failures with specific reasons
Test with known good sample data from dump1090

## Problem Description SkyView is filtering out several valid targets that dump1090 is able to show. This suggests we may have overly strict filtering or decoding problems that are rejecting legitimate ADS-B messages. ## Expected Behavior SkyView should be able to decode and display all valid aircraft that dump1090 can successfully process and display. ## Potential Root Causes - Decoding problems in the Mode S/ADS-B message parser - Overly strict validation in the beast protocol handler - CPR position decoding being too conservative - Message type filtering excluding valid aircraft - Signal strength thresholds being too high - Incomplete implementation of certain ADS-B message types ## Investigation Areas - **beast/parser.go**: Raw message parsing and validation - **modes/decoder.go**: Mode S/ADS-B message decoding logic - **modes/cpr.go**: CPR position decoding and validation - **merger/merger.go**: Data fusion logic that might filter out sources - Message type handling for DF17, DF18, and other formats ## Steps to Reproduce 1. Run dump1090 and SkyView simultaneously on the same data source 2. Compare the aircraft list between both applications 3. Identify aircraft visible in dump1090 but missing in SkyView 4. Analyze the raw messages for the missing aircraft ## Impact Missing valid targets reduces the effectiveness of SkyView for aircraft tracking and may cause users to miss important aircraft in their coverage area. ## Debugging Approach - Enable verbose logging to see rejected messages - Compare raw message handling between SkyView and dump1090 - Log validation failures with specific reasons - Test with known good sample data from dump1090

olemd commented

2025-08-25 08:30:45 +02:00

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Owner

Additional Information - Position Decoding Errors

Some targets that we do manage to decode are appearing hundreds of kilometers away from their actual position. This suggests serious issues with our CPR (Compact Position Reporting) decoding implementation.

Symptoms

Aircraft appearing at incorrect locations (100+ km offset)
Position jumps that are physically impossible
Decoded positions that don't match known airport/route locations

Likely Causes

CPR Global/Local Decoding Issues:
- Incorrect reference position for local CPR decoding
- Wrong latitude/longitude zone calculation
- Missing or incorrect odd/even frame pairing
Reference Position Problems:
- Using wrong reference position for relative decoding
- Not properly handling position ambiguity near zone boundaries
- Incorrect handling of surface vs airborne position formats
Implementation Bugs:
- Integer overflow in position calculations
- Incorrect scaling factors for lat/lon conversion
- Wrong constants in CPR algorithm implementation

Critical Areas to Review

modes/cpr.go: Complete review of CPR decoding algorithm
Position reference selection logic
Odd/even frame synchronization
Zone boundary handling
Surface position vs airborne position differentiation

This position error issue is likely related to the filtering problem - we may be rejecting correctly decoded positions as 'impossible' while accepting incorrectly decoded ones.

## Additional Information - Position Decoding Errors Some targets that we do manage to decode are appearing hundreds of kilometers away from their actual position. This suggests serious issues with our CPR (Compact Position Reporting) decoding implementation. ### Symptoms - Aircraft appearing at incorrect locations (100+ km offset) - Position jumps that are physically impossible - Decoded positions that don't match known airport/route locations ### Likely Causes 1. **CPR Global/Local Decoding Issues**: - Incorrect reference position for local CPR decoding - Wrong latitude/longitude zone calculation - Missing or incorrect odd/even frame pairing 2. **Reference Position Problems**: - Using wrong reference position for relative decoding - Not properly handling position ambiguity near zone boundaries - Incorrect handling of surface vs airborne position formats 3. **Implementation Bugs**: - Integer overflow in position calculations - Incorrect scaling factors for lat/lon conversion - Wrong constants in CPR algorithm implementation ### Critical Areas to Review - **modes/cpr.go**: Complete review of CPR decoding algorithm - Position reference selection logic - Odd/even frame synchronization - Zone boundary handling - Surface position vs airborne position differentiation This position error issue is likely related to the filtering problem - we may be rejecting correctly decoded positions as 'impossible' while accepting incorrectly decoded ones.