Subject: Decimal digits for Latitude and Longitude: 0.001&quot; Lat/Long<br/>
Date: Sep 08, 2004 @ 14:33<br/>
Author: Ron McConnell (&quot;Ron McConnell&quot; &lt;rcmcc@...&gt;)<br/>
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<div id="ygrps-yiv-577983511">In working on a question our Dave Patton<br/>
posted on the comp.info.gis and sci.geo.cartography<br/>
netnews groups about the US-Canada border monuments<br/>
# 194 and # 195 and a plaque, and whether the plaque<br/>
is on or south of the border as defined by<br/>
the line of sight between monuments,<br/>
I discovered that while my GCGC great circle, etc.<br/>
program takes in many digits (often more than<br/>
justified by the accuracy of the data)<br/>
and used them for calculations,<br/>
for some long forgotten reason, I had<br/>
limited the digits on output to only 6 good ones.<br/>
When getting down to milliseconds of latitude<br/>
and longitude and inches and centimeters of distance<br/>
this gets important.<br/>
The GCB program didn&#39;t have the problem.<br/>
<br/>
The plaque seems to be about 7.47cm or 2.94in<br/>
south of the border, subject to correction.<br/>
I&#39;m sure about the .47cm part, just not the 7. part.  :)<br/>
<br/>
I have posted an update of GCGC on my website,<br/>
mainly for such close distance uses of BoundaryPoint folks.<br/>
Amateur radio operators for whom GCGC was<br/>
originally intended work in much longer distances<br/>
like 100s or 1000s of kilometers or miles.<br/>
<br/>
[from sci.geo.satellite-nav netnews group]<br/>
<br/>
&quot;I am a surveyor and use differential GPS every day.<br/>
I can achieve accuracies of less than 20mm<br/>
in xyz in clear areas.&quot; - Mark  <a rel="nofollow" target="_blank" href="mailto:xxx@...">xxx@...</a><br/>
<br/>
From  Sigurd Humerfelt&#39;s web site notes on<br/>
  &quot;The Earth According to WGS 84&quot;<br/>
   &quot;Every degree of Latitude&quot;<br/>
<br/>
  &lt;<a rel="nofollow" target="_blank" href="http://home.online.no/~sigurdhu/Grid_1deg.htm">http://home.online.no/~sigurdhu/Grid_1deg.htm</a>&gt;<br/>
<br/>
N/S 49° (theoretical US-CA border)<br/>
1 min lat = 1853.50 m     1 min long= 1219.53 m		<br/>
1 sec lat =    30.8917 m  1 sec long =  20.3255 m<br/>
<br/>
Then at N/S 49º  <br/>
          20mm Lat  = 0.02m / 30.8917m/&quot; = 0.0006474&quot; Lat<br/>
<br/>
          20mm Long = 0.02m / 20.3255m/&quot; = 0.0009840&quot; Long<br/>
<br/>
Or better than 0.001&quot; of Lat and Long with DGPS<br/>
<br/>
This is consistent with &quot;altheiak&#39;s&quot; MDVADC<br/>
surveyor&#39;s lat/long data to 0.001 seconds.<br/>
Be skeptical about anyone who claims better than that<br/>
or puts more into or out of a computer program.<br/>
            <br/>
Cheers, 73,<br/>
<br/>
Ron McC.<br/>
<a rel="nofollow" target="_blank" href="mailto:w2iol@...">w2iol@...</a><br/>
<br/>
Ronald C. McConnell, PhD<br/>
<br/>
 WGS-84: N 40º 46&#39; 57.6&quot;  +/-0.1&quot;<br/>
         W 74º 41&#39; 22.1&quot;  +/-0.1&quot;<br/>
         FN20ps.77GU31 +/-<br/>
         V +5058.3438  H +1504.2531<br/>
<br/>
 <a rel="nofollow" target="_blank" href="http://home.earthlink.net/~rcmcc">http://home.earthlink.net/~rcmcc</a> <br/>
<br/>
&quot;Any sufficiently advanced science<br/>
is indistinguishable from magic.&quot;<br/>
  - Arthur C. Clarke</div>