<div>The points are my property irons and were in SC State Plane (with international foot) and I had to convert to WGS84. Around these parts using NAD27 gives an error of about 125' to the north if I recall correctly. Further, the azimuth from the property iron to the point varied by about 120 degrees depending on which point I was at. It wasn't like I was consistently off 20 feet to the north for example.</div>
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<div>Just to be more specific about my question, I was hoping for someone who had recently been to the middle east where the US would want to have a degraded service. Maybe such a person could tell me if SA was on over there like it was everywhere in the 1990's?</div>
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<div>Footnote: the international foot is based on the redefined inch that is exactly 2.54cm. The imperial inch and US inch were "averaged" to 2.54cm in 1959 or so. So in other words, we here in South Carolina are progressive enough to recognize and use a modified inch derived from metric, but we won't actually _use_ metric. sigh.... for what it's worth, the difference in the old inch and the "new" inch makes about a 6 foot difference across the state from the westmost to the eastmost point. I think AZ is the only other state to use the international inch. We sure make things hard on ourselves.</div>
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<div>Wes<br><br></div>
<div class="gmail_quote">On Mon, Nov 23, 2009 at 10:00, Mark Earle <span dir="ltr"><<a href="mailto:wa2mct@mearle.com">wa2mct@mearle.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">
<div class="im">n4lbl wrote:<br>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">I've always presumed that the accuracy reported is at some particular<br>confidence interval but I surely don't know that. If the GPS says the<br>
accuracy now is 10 feet that sounds like a 100% confidence interval is<br>implied but I have trouble believing that.<br> <br></blockquote></div>Something else to consider - what map datum is being used for the "known" point? For instance, if I stand at a USGS benchmark, my GPS might report 15' error of position. But, what map datum is my GPS using, vs the Benchmark coordinates? This must be accounted for.<br>
<br>My Nuvi350, as far as I can find, the map datum is not selectable. My old GPS45XL offers many to choose from. This is handy, for instance, when doing tower siting work - my GPS datum can agree with the FCC databases, no conversions required after the fact.<br>
<font color="#888888"><br>-- <br> ) ) de WA2MCT Mark<br> ( ( Echolink 221408 Grid Square EL17HQ<br> ) ) You will be assimilated... oooh, coffee!!<br> _|****| <a href="http://www.findu.com/cgi-bin/find.cgi?wa2mct-7" target="_blank">http://www.findu.com/cgi-bin/find.cgi?wa2mct-7</a> Home<br>
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