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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Hi Xavier<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>I tried your approach and like it a lot.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Unfortunately I get the same result; <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>-specified std errors result in gross
distortion,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>-no std errors give accurate survey plot
(but forced to specified gps location without accounting for it’s
inaccuracy)<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Other ideas?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Perhaps it’s time to try 5.3.12<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Bruce<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 color=black face=Tahoma><span
style='font-size:10.0pt;font-family:Tahoma;color:windowtext;font-weight:bold'>From:</span></font></b><font
size=2 color=black face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma;
color:windowtext'> therion-bounces@speleo.sk [mailto:therion-bounces@speleo.sk]
<b><span style='font-weight:bold'>On Behalf Of </span></b>Xavier Pennec<br>
<b><span style='font-weight:bold'>Sent:</span></b> Sunday, 22 December 2013
9:52 p.m.<br>
<b><span style='font-weight:bold'>To:</span></b> therion@speleo.sk<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [Therion] fixed point
std error causes extreme survey network distortion</span></font><font
color=black><span style='color:windowtext'><o:p></o:p></span></font></p>
</div>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3 color=black
face="Times New Roman"><span style='font-size:12.0pt'>Hi Bruce,<br>
<br>
I have hundreds of fixed points with different accuarcy and never noticed the
effect you are describing. However, I am not fixing directly the coordinates of
stations of my survey. I always create independant fixed points and then equate
them to the survey stations. In your case, this would give something like:<br>
<br>
fix GPS_12 1562372 5439558 992 20 20
20 # entrance<br>
equate GPS_12 12@01<br>
fix GPS_0 1562117 5440239 1080
5 5 20 # another entrance<br>
equate GPS_0 0@10<br>
fix GPS_120 1562124 5439500 1020 10 10 10
#entrance three<br>
equate GPS_120 120@05<br>
<br>
An advantage of this strategy is that I can comment all the equates but one to
start with and verify with Aven on the 3d file where are the GPS points located
with respect to the cave survey. That way, I can spot the outliers in the GPS
points (or the errors in their retranscription) and iteratively validate the
equates.<br>
<br>
Xavier<br>
<br>
PS: between us, I would not qualify your gps stddev below as very rough. A
stddev of 5 meters about the smallest I use when I get long GPS averages (more
than 30 minutes) with one of the a differential satellites. <br>
<br>
<br>
<o:p></o:p></span></font></p>
<div>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'>Le 22/12/2013 01:35, Bruce a écrit :<o:p></o:p></span></font></p>
</div>
<blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'
cite="mid:305BEB3C9A2A4F49ADE1BAE2C6A77A91@JUICEBRAIN" type=cite>
<p class=MsoNormal><font size=2 color=black 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.<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span lang=EN-NZ
style='font-size:10.0pt;font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span lang=EN-NZ
style='font-size:10.0pt;font-family:Arial'> fix 12@01
1562372 5439558 992 20 20 20 # entrance<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black 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<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black 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<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span lang=EN-NZ
style='font-size:10.0pt;font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black 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.<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black 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.<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span lang=EN-NZ
style='font-size:10.0pt;font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black 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.<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span lang=EN-NZ
style='font-size:10.0pt;font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black 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;<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span lang=EN-NZ
style='font-size:10.0pt;font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span lang=EN-NZ
style='font-size:10.0pt;font-family:Arial'> fix 12@01
1562372 5439558 992 #20 20 20 entrance<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black 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<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black 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<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span lang=EN-NZ
style='font-size:10.0pt;font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black 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.<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black 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.<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span lang=EN-NZ
style='font-size:10.0pt;font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span lang=EN-NZ
style='font-size:10.0pt;font-family:Arial'>Anyone else having problems like
this?<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black 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?<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span lang=EN-NZ
style='font-size:10.0pt;font-family:Arial'>Or is it a bug?<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span lang=EN-NZ
style='font-size:10.0pt;font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
lang=EN-NZ style='font-size:12.0pt'>Bruce<u1:p></u1:p></span></font><font
color=navy><span style='color:navy'><o:p></o:p></span></font></p>
</blockquote>
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