Altitude

[epieroceanit]

I'm trying to understand how altitude is decoded when the Q bit is 0 - i.e. the high altitude format. I see that in py_common.py you have code for this, but when I run it on some ADS-B messages that I know are in high altitude format, I get suspiciously low values. For example, 8dae0b205980a5f75293fdc1e60d has an altitude of 200 ft. Do you have a reference for where you got the algorithm you coded?

[xoolive]

We use the same code here, all references as signposted
https://github.com/xoolive/jet1090/blob/a457b1f90d3fcda2edcfb525d014158df5844efd/crates/rs1090/src/decode/bds/bds05.rs#L73

8dae0b205980a5f75293fdc1e60d decodes as follows, which doesn't sound outrageous as is...

{"df":"17","icao24":"ae0b20","bds":"05","tc":11,"NUCp":7,"NICb":1,"altitude":200,"source":"barometric","time_sync":false,"parity":"odd","lat_cpr":64425,"lon_cpr":37885}

[epieroceanit]

Thank you for the quick response. I've tracked down some authoritative documents (likely bootleg). So, I'll use those to try to validate your code. I'll let you know what I find.

[epieroceanit]

Good, news! I have verified that your code is correct.

For the record, I have attached these two files that I used as references:
1090-WP30-18-DRAFT_DO-260B-V42.pdf
Annex 10 Volume IV.pdf

The first is a draft of the official standard that I managed to find, so not definitive, but very likely accurate, and I didn't have to spend a few $k on it. You want page 59. That refers to the second document, page 3-94.

The Q=1 encoding is not well documented in the open literature, and many open source projects don't implement it, so kudos to you for doing a good job with it, and thank you again for the reply to my original post.