wpietri / simpleais Goto Github PK

First, thanks for your work on simpleais, it is quite useful.

I noticed that simpleais reports bad longitude/latitude values for message 27. The root cause appears to be that _parse_lon/_parse_lat use a scale factor of 4 (10^4) regardless of message type, which gives incorrect results for message 27. Message 27 longitude/latitude has a lower resolution (degrees/10) than other AIS message types (degrees/10000).

Excerpt from the standard:

Cheers

Message type 24 comes in two variants, called "part A" and "part B". simpleais always returns both sets of fields.

Example message: !AIVDM,1,1,,B,H5NhCmTN7B=400500000001P0004,0*56

Decoded by simpleais:

type 24
repeat 0
mmsi 367793110
partno 1
shipname G!4#Q@@AP@@@@@@@X
ignored-160 4
shiptype Fishing
vendorid GRM
model 1
serial 5
callsign
to_bow 12
to_stern 0
to_port 0
to_starboard 0
mothership_mmsi 25165824
ignored-162 4
text None

Correct decoding (via Maritec):

type 24
repeat 0
mmsi 367793110
part_no 1
type fishing
vendorid GRMD@@E
callsign @@@@@@@
to_bow 12
to_stern 0
to_port 0
to_starboard 0
spare 4

The output for shipname may be uninitialized memory, at one occasion I got C: DRIVE - Edit: Never mind, there's a ship with that name :)

This type may require some custom handling as the documentation for AIVDM merged both definitions into the same table:
https://gpsd.gitlab.io/gpsd/AIVDM.html#_type_24_static_data_report