<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">I would like to add that this new process was put into place several weeks ago as part of an ongoing task of moving dependencies from the old VAX to modern technology, and the bug was discovered only recently. We will work to prevent errors like this in the future.<div><br><div>
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-webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Verdana; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; color: rgb(0, 0, 0); font-family: Verdana; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; -webkit-text-decorations-in-effect: none; text-indent: 0px; -webkit-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><font face="Verdana, Helvetica, Arial"><span style="font-size: 12px; ">-<span class="Apple-converted-space"> </span><font class="Apple-style-span" face="'Handwriting - Dakota'" size="3"><span class="Apple-style-span" style="font-size: 13px; ">Lisa</span></font><br><font><font class="Apple-style-span" color="#008500">--------------------------<br></font></font></span><font><span style="font-size: 11px; "><font class="Apple-style-span" color="#008500">Lisa Wald, Geophysicist</font></span></font></font></div><div><font face="Verdana, Helvetica, Arial"><font><span style="font-size: 11px; "><font class="Apple-style-span" color="#008500">Web Team Manager/Project Manager<br>USGS Earthquake Hazards Program<br>Golden, CO<br>303-273-8543<br><a href="mailto:lisa@usgs.gov">lisa@usgs.gov</a><br></font></span></font></font></div></div></span></div></span></div></span></div></span><span class="Apple-style-span" style="font-size: medium; "><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span class="Apple-style-span" style="font-family: Verdana, Helvetica, Arial; font-size: 12px; color: rgb(0, 133, 0); ">--------------------------</span></div></span></div></span></div></span></div></span></div></span></div></span></div></span></div></span></div></span></div></span></div></span></div></span></div></span></span>
</div>
<br><div><div>On Apr 8, 2011, at 2:05 PM, Matthew J Donnelly wrote:</div><br class="Apple-interchange-newline">
<br><font size="2" face="sans-serif">The Problem: It was found that
the bearing function used in nearest cities incorrectly calculated bearing
if it required going over the 180 degree meridian. Also on further
inspection, the algorithm it was using has great distortion of the bearing
when at high latitudes. </font>
<br>
<br><font size="2" face="sans-serif">The Solution: I developed a simple
methodology for determining if the bearing crosses 180 and the way to handle
bearing in that case. I also replaced the existing algorithm that
calculates bearing by using Rhumb line (basically the planar bearing) with
one that calculates it using a Great Circle calculation. By using
the Great Circle it seems to have fixed the distortion we saw at high latitudes.
</font>
<br>
<br><font size="2" face="sans-serif">Matthew</font>
<br>
<br><font size="2" face="sans-serif">-------------------------<br>
Matthew J Donnelly<br>
Information Technology Specialist<br>
National Earthquake Information Center<br>
US Geological Survey<br>
Golden, CO 80401<br>
Ph: 303-273-8590<br>
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