Compact Position Reporting

[max]

OK, I started a new thread as I have finished my first pass at the code.  Alas, I picked a few table values and they give me poop.

But maybe the table values are wrong??

Does anyone have a set of values I can use?  latEven, latOdd, LonEven, LonOdd, lasttype(even or odd)  = latitude and longitude

[DaveReid]

Does anyone have a set of values I can use?  latEven, latOdd, LonEven, LonOdd, lasttype(even or odd)  = latitude and longitude

Squitter                     Lat        Lon
58 93 05 2A 01 BE 92   50.5892  -1.2779
58 91 85 2B 01 BE FB   50.5952  -1.2699
58 A1 05 0B D1 49 BE   50.4093  -3.5597
58 A1 05 0E 41 49 85   50.4238  -3.5640
60 89 55 08 D1 B8 72   50.3914  -1.3975
58 A1 05 20 81 49 2C   50.5326  -3.5708
58 A1 05 29 E1 49 B7   50.5885  -3.5602
58 A1 05 2B 51 49 CE   50.5970  -3.5585
58 A1 05 35 01 4A 64   50.6547  -3.5470
58 A1 05 35 21 4A 66   50.6555  -3.5469
90 C3 85 15 10 63 FD   50.4644   1.9528
60 71 15 34 E1 C1 FB   50.6540  -1.2113
58 A1 B5 32 61 6A 4D   50.6391  -2.9238
58 9B 65 36 21 6F D8   50.6614  -2.8155
58 69 D5 1C 51 C4 F5   50.5076  -1.1531
58 69 A5 1C E1 C5 15   50.5110  -1.1507
58 69 75 1D 71 C5 34   50.5143  -1.1483
60 C3 85 CA 67 EB FB   51.5450  -0.3910
60 7B 01 ED 21 99 7C   50.8894  -1.9481
58 83 05 AB 41 DA C0   51.3594  -0.7275

Plenty more where those came from !

HTH
Dave

[max]

It's worse than that.  You need an even and an odd from the same airplane...

Thanks Dave, I found what I was looking for in the CPR explanation document I noted earlier.  So with:

globalAirbornePosition(0x035f0, 0x0a3f9, 0, 0x10000, 0)     //  latEven, latOdd, lonEven, lonOdd, last (even = 0, odd = 1)

My output gave me:

Latitude/Longitude: -77.367920/180.000000

Only have 50 billion more tests 

[DaveReid]

It's worse than that.  You need an even and an odd from the same airplane...

Not necessarily, if you know for sure that the position of the aircraft is within 180nm of a reference point, you can use a single even or odd transmisson.

[junglejet]

Hadn't you got a piece of code from the soviet foreigner some time ago? is it a conversion to Java or what are you trying?

[DaveReid]

Hadn't you got a piece of code from the soviet foreigner some time ago? is it a conversion to Java or what are you trying?

Yes, I've seen Boris's code, but by that time I had already written by own routine that's embedded in my packet capture program.

[max]

Yea, I've been sitting on a lot of code, but doing other stuff.

Now that I have this really cool ADS-B receiver that gives me raw data without all the proprietary bullshit...

I didn't really understand the code that well, but I have a Masters degree in bit-twiddling now!  The CPR documentation actually makes sense.  I was then able to write my own code as I read the document.  When I got done I could see a lot of what I wrote has duplicated a lot of what the friend of Boris wrote in Pascal.  Pascal is easy enough to decode for an old C programmer, but putting it in a class object was kind of fun.

I'm ready now to have my CPR Object process DF17 Objects and plot some crap on the screen  

The SBS-1 digital board is pretty much history now...

Edit: Oh yea, the document gave me a curve by talking about 17 bits, 19 bits and 12 bits, but this really is for the encoder.  The decoder is always getting 17 bits.  That really messed me up for a bit until I made sure I was on the decoder page, and not the encoder page. Argh!

[max]

Speaking of encoding.  I guess, if you want to use the local position algorithm with an user configured lat/lon fixed location (like Kinetic does), you would need to encode the lat/lon to both even and odd bins right?

I'm just thinking out loud I guess, on whether to not worry about that, and just wait for a good global position before computing the local position.

I have seen a lot of odd only position reports when sniffing the data (or even), and you'd have to let all this good data fly by because you don't have a global even/odd position in the table for 10 seconds. Whereas, if you had a user entered value, you could start producing lat/lon positions with just an odd or just an even as the bloke was moving along the taxi-ways, or flying behind the building between you and the runway.

Do you guys encode the user configured position, or just wait for a global?

[DaveReid]

Don't get too hung up on that 10-second interval - you can use a longer interval as long as you can be sure that the target hasn't moved more than 3nm between odd and even format reports. 

An aircraft would have to be flying at 1080kt GS to cover that amount of ground in 10s.

[junglejet]

The worst thing that can happen with local decoding is the target is placed in the next zone. There it would be dancing forth and back.