Decoding ADS-B data from the SBS-3

[eyl]

Hello everyone, new user here.Hope I put this in the right subforum

I'm using an SBS-3 with BaseStation to read flight data. I need to obtain the following information:

1) Latitude
2) Longitude
3) GNSS Altitude
4) Message time.

As I'm very new to ADS-B, I have some questions regarding this:
1) As I understand, Data Format 17, which contains the flight information, includes several message types (e.g. Type 11 includes Airborne Position data, while Type 19 includes velocity data). It seems to me that in order to get all the information above for a given point, I will need both an airborne position message of type 9-18 (for lat/lon, ignoring for the moment that I require two messages due to the CPR encoding, and barometric altitude) and a velocity message of type 19 fo the difference between the barometric altitude and AE, or alternatively a position message of type 20-21. How often are these transmitted? That is, does a single DF17 squawk include all the 31 message types, or are different types  transmitted at different times?
2) What would be the best way to extract the data from the SBS? I've tried getting the raw data from port 30006 with BaseStation 1.84. The attached file shows the obtained output. However, I don't understand how to decode it; I can't figure out how to tell where a message begins and ends.
3) It's my understanding that the message transmission time can be deduced by finding  the closest previous even or odd (depending on the value of the message's time bit) UTC 200ms time tick relative to the message'sreception (assuming the  receiver is synchronized with UTC). Is this correct?

Thanks!

[Attachment deleted by Admin to save file space]

[Anmer]

Welcome

Have you seen the Kinetic API Reference document?

http://www.kinetic.co.uk/DownloadFiles/API/KineticAPIDoc_104.pdf

[eyl]

Hello Anmer!

I'd actually forgotten about that doc, thanks.

If I understand that document correctly, then if I look at a given line in the text file I attached in the first post, it is composed of a sequence of groups, each of which consists of 3 prefix bytes (DLE, STX, packet type), then (for ADS-B messages) 4 additional bytes (1 not used and 3 for timestamp) then 14 bytes of data, and concluded by 4 last bytes (DLE, ETX, 2xCRC), and then the next message begins. So if I look at the second line in that file, for example, it consists of 4 messages, one DF15 and 3 DF17. Is this correct? Also, what is the timestamp relative to?

[Anmer]

Unfortunately I don't have any experience of the messages.

Maybe someone else here can answer?