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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 got some unexpected results recently when I added some
very rough gps coordinates to my survey for a cave that has three entrances.
Because they are approximate I added some estimates of standard errors as below,
so that I could get Therion to factor the relative accuracy into the loop
closure.<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'> fix 12@01 1562372 5439558
992 20 20 20 # entrance<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'> fix 0@10 1562117
5440239 1080 5 5 20 # another entrance<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'> fix 120@05 1562124 5439500 1020 10
10 10 #entrance three<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'>With any ONE of the entrances fixed as above, the
cave plots accurately – I can verify this in Google Earth.<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'>As soon as I have any two or more entrances fixed,
then the cave distorts significantly, and the entrances are stretched some
hundreds of metres away from the centroid of the cave. Also quite often
getting ‘scrap exceeding maximal scale’ errors if I output to pdf.<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 checked this was not just a feature of that dataset
by mocking up a similar situation in two other datasets, and got similar
results.<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'>The work around seems to be to avoid using the
standard errors;<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'> fix 12@01 1562372 5439558
992 #20 20 20 entrance<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'> fix 0@10 1562117
5440239 1080 #5 5 20 another entrance<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'> fix 120@05 1562124 5439500 1020 #10
10 10 entrance three<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'>but this then results in each gps location receiving
equal weighting.<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 think I might have noticed this problem a few years
ago, and gave up on trying to sort it out because I wasn’t able to
identify the characteristics of the problem well enough.<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'>Anyone else having problems like this?<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'>Or identify a reason why what I am trying to do is
not possible?<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'>Or is it a bug?<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>
<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'><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>
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