Well, time to eat my pride here and put it out there on the off chance it helps someone else.
I’ve gone interstate and have found the same distance error in my coordinates. Begged the question, ‘what am I missing with this consistently inconsistent nature. NMEA vs decimal degrees my friends. Native output of the coordinates are something I have never heard of before which kept throwing me about 40kms out. A simple conversion inside the pi then outputting decimal degrees and we’re away!
Thanks for all your help and patience, I now am operational!
I’m sure you’re not the first that got tripped up on that one.
There’s a good reason for that native format. The NMEA character set is very limited, in order ensure that it is as universal as possible, and the era in which it was developed was a time when 4800 bd was a pretty good effort for reliable data transmission, so it had to be as compact as possible. To get degrees, minutes and seconds into a format as small as possible meant avoiding unnecessary separators. So the standard takes advantage of the fact that minutes will always be 0 to 59. But if minutes are always formatted as two digits (potentially one wasted character), and the decimal point is the only required separator, then leading zeroes are not required for degrees, there is a no need for a separator between degrees and minutes, and the decimals can be as long as the precision requires. It’s quite a good compromise.
The limitations imposed by some of the early design decisions are really obvious with AIS, where there is a lot of plain text involved. The question was “How do you compress the text, but still end up with a compressed string that can be represented with 6-bit ASCII?”. They did it, but unravelling how it was done is a nightmare.
Glad to hear we’re no longer lost and that your project is up and running! Really appreciate you coming back to share how you diagnosed the issue, I’m sure it will help future travellers facing the same problem.
The same could apply to time. Most calculators would have a conversion from Hr, Min, Sec to decimal Hr and the reverse. I know my old HP C10 of 1882 vintage has. This of course can be used as a degree conversion as well.
My poor old calculator, the battery connection broke so I am going to stick a 3 AAA cell holder on the back. Pretty difficult to find a RPN calculator these days. Swiss Micro actually still manufacture copies of the old HP devices at a price. Not the C10 though but the C11 (slightly up market) or I have found a Computer based and Phone based devices which are pretty much a replica of HP.
Cheers Bob
Hi Danny
Simple fix in the end. Don’t feel too bad about it. As Jeff said you won’t be the first or the last. It looks like no one here thought of this so a feather in your cap.
Thanks for the heads up on the result. I am sure most readers of this thread will tuck this one away somewhere useful.
The result you originally posted is still confusing. Does “2463.036061,S” mean 2643.036061 minutes or 26Deg 43.036061Min. I would be interested to know. My thought would be the latter but I just don’t know and can’t dive into the finer details of that Hat at the moment as I am not at home.
Cheers Bob
The NMEA coordinates it spits out are (as close as I can tell) quite literally translated from 2643.036061 S to 26Deg 43min 03.6 sec. I would have thought the 43 would be decimal bringing it back to about 25min, but no. It is a literal translation despite the strange decimal point placement.
Anyhoops, the project moves forward! Thanks again team:)
Hi Danny
Thanks. I had an idea it could be something strange like that.
If you look at the E number and think the complete number could be decimal minutes it would be something like 255 Deg. It can’t be more than 180 Deg as that would be past the date line and the position would be XX Deg “W”.
Good you could establish your actual position and spot the repeating error and get it sorted.
Cheers Bob
Really appreciate you coming back to share how you diagnosed the issue, I’m sure it will help future travellers facing the same problem.
