From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lyndon Nerenberg To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net> In-reply-to: References: <7aa20b1cedd55fec@orthanc.ca> <7aa20bbcd81bbf89@orthanc.ca> <7aa20bcbe33e607c@orthanc.ca> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <49437.1539289415.1@orthanc.ca> Date: Thu, 11 Oct 2018 13:23:35 -0700 Message-Id: <7aa20be8f44325c6@orthanc.ca> Cc: Lyndon Nerenberg Subject: Re: [9fans] PDP11 (Was: Re: what heavy negativity!) Topicbox-Message-UUID: ed0201b4-ead9-11e9-9d60-3106f5b1d025 hiro writes: > don't you need sending ability, too for AIS? No, a receive-only setup is very useful on a small boat. Where I would like to go with this is to take the decoded AIS data as input for "ARPA" style collision plots. I'm interested in the big boats sailing through the straight. They can't turn fast, and rarely change course. If I can derive their intentions, I can plot a path between them that requires the least amount of tacking. The big boats, in turn, have no interest in us little critters. They actively filter out the "class B" (I think that's the term) noise that are AIS transmissions from the small craft. Even if we hit them, we can't sink them, so they don't care about us. Therefore there is no incentive for small boats to transmit AIS. Unless you're trying to locate your buddies for a tie-up somewhere. (That can be a very valid reason for transmitting!) --lyndon