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<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>I have a mystery, whereby an overland survey between
two fixed points gives a correct pdf plan output with;<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>loop-closure survex<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>(I know it is ‘correct’ because the
aerial photograph image matches the features surveyed) but if I specify;<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>loop-closure therion<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>then one of the fixed points is about 150m misplaced
in plan and the surveyed features are clearly in the wrong place.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>In both scenarios therion.log reports identical
average loop errors and specific loop error statistics. The error over a
500m loop is about 2.3%, mainly due to a 12m error in elevation (can not trust
those gps readings). The plan error if one of the points has its ‘fixity’
removed is about 4m, and the plots produced are correct regardless of the loop
closure method.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>It is a rather large dataset with many underground loops,
and four fixed surface points. Two of which have overland surveys between
them. Only one of the overland surveys has this problem.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>Using Therion 5.3.5. Can replicate this result
on three computers.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>Any theories as to what might be going on and how to
locate the issue?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>Bruce<o:p></o:p></span></font></p>
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