Is ROT(Turn) decoding properly? about pyais HOT 4 CLOSED

Hey @bgercken,

a lot going on here. I try to answer your questions 1 by 1 :-D.

I am seeing a lot of sentences where the value for "turn" is being set to None

This is intentional. Turn rate is encoded as follows :

• 0 = not turning
• 1…​126 = turning right at up to 708 degrees per minute or higher
• 1…​-126 = turning left at up to 708 degrees per minute or higher
• 127 = turning right at more than 5deg/30s (No TI available)
• 127 = turning left at more than 5deg/30s (No TI available)
• 128 (80 hex) indicates no turn information available (default)

If no turn information is available the turn field is set to None.

Now I have a new question to consider. It appears that you may be rounding the product before squaring it when converting from the raw value to the decoded field value.

I think you are right. The GPSD project - the de facto reference documentation for this project - does not even round: https://gitlab.com/gpsd/gpsd/-/blob/master/devtools/ais.py#L117. So I dropped the round statement and it seems to work correctly.

However, I am not 100% sure, since the values for ROT vary slightly from decoder to decoder. Depending on the decoder, there seems to be a certain confidence interval of +/- 5 degrees, in which all available decoders scatter. 🤷

Anyways, thank your the tip.

from pyais.

OK - I figured out why the online decoder did not match your values - on his site he is just showing the raw value and not the converted value as you do in your code. Sorry, my mistake.

from pyais.

Now I have a new question to consider. It appears that you may be rounding the product before squaring it when converting from the raw value to the decoded field value.

Currently on line 543 in messages.py:

       return math.copysign((round(turn / 4.733)) ** 2, turn)

Should it be?
       return math.copysign(round((turn / 4.733) ** 2), turn)

Thanks.

from pyais.

Closed by #74

from pyais.