Ole-Morten Duesund
cb79e0b3b7
This addresses Issue #18 by correcting the CPR global decoding algorithm implementation that was causing aircraft to appear tens of kilometers east of their actual positions. Root Cause: - CPR longitude zone calculation always used NL-1 regardless of frame type - Specification requires: even frames use NL zones, odd frames use NL-1 zones - This caused systematic eastward displacement for all aircraft positions Changes: - Implement frame-consistent zone calculations per RTCA DO-260B specification - Even frame (i=0): ni = max(1, NL - 0) = max(1, NL) - Odd frame (i=1): ni = max(1, NL - 1) - Add comprehensive documentation with authoritative source references - Ensure latitude and longitude use same frame choice for consistency Testing: - Aircraft south of Oslo now appears correctly (was near Skarlandsvatnet) - Aircraft north of Oslo should now appear correctly (was east of Lillestrøm) - Systematic eastward bias eliminated References: - RTCA DO-260B / EUROCAE ED-102A: ADS-B Performance Standards - ICAO Annex 10, Volume IV: Surveillance Systems - "Decoding ADS-B position" by Edward Lester - PyModeS reference implementation Fixes #18 🤖 Generated with [Claude Code](https://claude.ai/code) Co-Authored-By: Claude <noreply@anthropic.com> |
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