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[aprssig] Cruise Ships, APRS.FI, and AIS

Wes Johnston, AI4PX wes at ai4px.com
Thu Jan 15 23:26:20 UTC 2009


Amen to this... it's a bad idea to convert data from one format to another
in transit.

At one time (10 years ago) , I had the bright idea to catch a packet at the
first hop and if I knew it was the first hop, convert NMEA sentences from a
'dumb' kpc3 tracker to mic-e format.  The idea was to save bandwidth by
reducing the lenght of the original packet 80bytes to 32 bytes.  The problem
was that there was no way to know that my digi was the only digi to hear the
packet on the first hop, and we ended up with two different packets
circulating the network with the same information at the same time.

Another example was in WinAPRS they did the conversion to mic-e on the fly
but due to different levels of precision in the NMEA and MIC-e format(or a
math error??), my car appeared to have double positions very close to one
another.

It's much better (ie correct) to force the clients to decode the data they
want to see rather than convert it for them.

Wes
---
It may be necessary temporarily to accept a lesser evil, but one must never
label a necessary evil as good.


On Thu, Jan 15, 2009 at 4:39 PM, Heikki Hannikainen <hessu at hes.iki.fi>wrote:

> On Thu, 15 Jan 2009, Earl Needham wrote:
>
> >    I wonder if there's a way to show these ships on UI-View...
>
> No, I don't think there is any proper way to do it. You can't expand
> UI-View to show AIS as such. Without converting AIS to APRS, which in turn
> isn't really possible to do well, since APRS packets don't have the fields
> required to transmit all the interesting extra information present in AIS
> packets.
>
> So, I think it's a bad idea to try to convert AIS (or ADS-B) data to APRS
> format, and if someone still decides to do it, it should never be fed into
> the APRS or APRS-IS networks.
>
>   - Hessu
>
>
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