<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">I agree with Kenneth’s proposal. Someday, we’ll need to be able to track objects up to <span style="font-variant-ligatures: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255);" class="">582,749,918 knots and if the speed field isn’t digit limited we’ll be able to. I’m a bit rusty on parsing APRS packets myself so I don’t recall what comes after the speed field. But if it has any kind of delimiter on it, it would be trivial to tweak an APRS client to look for that instead of counting characters.</span><div class=""><br class=""></div><div class=""><br class=""><div class="">
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<br class=""><div><blockquote type="cite" class=""><div class="">On Oct 12, 2017, at 11:30 AM, Kenneth Finnegan <<a href="mailto:kennethfinnegan2007@gmail.com" class="">kennethfinnegan2007@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">Ok, let's take a step back here, because this is getting a little crazy. Let's examine the original problem statement:<div class=""><br class=""></div><div class="">"The APRS course/speed data extension doesn't support speeds above 999 knots"</div><div class=""><br class=""></div><div class="">This means that no current APRS implementations support any changes we make here, and any changes we make will not be parsed correctly by any existing software.</div><div class=""><br class=""></div><div class="">For example, given this latest proposal, if the ISS were to beacon a speed of 779, every existing APRS implementation would rightfully so parse this as 779 knots, which is really really incorrect.</div><div class=""><br class=""></div><div class="">Given that none of the existing parsers will correctly handle these packets, why are we limiting ourselves to three digits? Why not just leave the field in knots and just have the ISS beacon their location with "120/15200"?</div><div class=""><br class=""></div><div class=""> 1. Existing parsers were going to get it wrong anyways, so they're going to misinterpret this course/speed as 152 knots instead of 779, an additional error of only 4%. They're already off by 95%, so the difference is immaterial.</div><div class="">2. Humans reading the packets will parse the packet correctly, which is certainly not the case with the proposed 135X-90000 equation.</div><div class=""><br class=""></div><div class="">So my proposal would be: </div><div class="">"For speeds above 999 knots, use more than three digits."</div><div class=""><br class=""></div><div class="">1. It's simple and human readable</div><div class="">2. It doesn't break the current expectation that the speed is in units of knots</div><div class="">3. It's limitlessly extensible, for when someone wants to encode any speed between or above any of the magic 99X values proposed earlier.</div><div class="">4. It doesn't suffer from reduced resolution for speeds above mach 1.</div><div class=""><br class=""></div></div><div class="gmail_extra"><br clear="all" class=""><div class=""><div class="gmail_signature" data-smartmail="gmail_signature">--<br class="">Kenneth Finnegan<br class=""><a href="http://blog.thelifeofkenneth.com/" target="_blank" class="">http://blog.thelifeofkenneth.com/</a></div></div>
<br class=""><div class="gmail_quote">On Thu, Oct 12, 2017 at 6:16 AM, Robert Bruninga <span dir="ltr" class=""><<a href="mailto:bruninga@usna.edu" target="_blank" class="">bruninga@usna.edu</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div lang="EN-US" link="blue" vlink="purple" class=""><div class="m_-6818501720658619223WordSection1"><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class="">In a move to keep APRS relevant, there was some useful feedback on the idea to extend the speed range of APRS reporting. I like the transition at Mach 1 (670 kts).</span></p><div class=""><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class=""> </span><br class="webkit-block-placeholder"></div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class="">So here is the way to handle speeds above Mach 1 and it works for both</span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class=""> MicE and CSE/SPD values of X speed field.</span></p><div class=""><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class=""> </span><br class="webkit-block-placeholder"></div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class="">If X Less than or equal to 670 then SPEED = X in Kts</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class="">If X is greater than 670 then SPEED is 135X -90000 in Kts</span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif" class=""></span></p><div class=""><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class=""> </span><br class="webkit-block-placeholder"></div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class="">You do not even need to do the math. You can just use some pre-calculated values shown here:</span></p><div class=""><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class=""> </span><br class="webkit-block-placeholder"></div><div id="m_-6818501720658619223divtagdefaultwrapper" class=""><p class=""><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class="">779 = 15,200 knots space station</span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif" class=""></span></p><p class=""><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class="">682 = 2100 knots Mach 3</span></p><p class=""><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class="">678 = 1600 knots military</span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif" class=""></span></p><p class=""><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class="">677 = 1340 knots Mach 2</span></p><p class=""><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class="">675 = 1200 knots Concorde</span></p><p class=""><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class="">670 = 670 knots Mach 1</span></p><div class=""><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class=""> </span><br class="webkit-block-placeholder"></div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class="">These remain in Knots because that is the APRS standard for speed, but of course you can also display them in MPH if you want to make that conversion which I think all PILOTS use.</span></p><div class=""><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class=""> </span><br class="webkit-block-placeholder"></div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class="">Bob, WB4APR</span></p><div class=""><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d" class=""> </span><br class="webkit-block-placeholder"></div><div class=""> <br class="webkit-block-placeholder"></div></div></div></div>
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