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First post here.

At work yesterday undertaken a traverse to install lost control stations down the motorway with a Leica ms50 1”. 

Approx 18 stations were installed prior to starting, known backsite method was used from two existing control stations approximate loop length circa 2000m.

Everything seemed to be going well with no massive errors throughout the traverse but upon closing back to the two original stations the Hz dist was within 20-30mm and height 3mm  but there was a great angular error amounting to almost 200+mm in position. Has anyone experienced anything like this before? All the usual things were checked, prism offsets,heights, co ordinates, atr check and adjust.

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VA LS 2867
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It could be the result of a linear traverse with angles close to 180°.  You should have some cross tie checks along the traverse.  If the traverse legs were close to 180°, I have experienced large closure errors like what you are seeing.  I would perform some GPS observations as a position check on a couple points at each end and the middle.

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Bill93
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Posted by: VA LS 2867

It could be the result of a linear traverse with angles close to 180°.  You should have some cross tie checks along the traverse.  If the traverse legs were close to 180°, I have experienced large closure errors like what you are seeing.  I would perform some GPS observations as a position check on a couple points at each end and the middle.

The only problem with angles close to 180 is that you can lose track of whether it was measured as an angle right or angle left, and that shows up as a serious closure error.

Nowadays everybody gets angle and distance of comparable accuracy, so it doesn't really matter what the angle is when using both values.

Of course, a short traverse leg will usually give a lot more angle error due to the effects of mis-centering, which will affect the angular closure a lot more than it does the positional closure.

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trav

It's a weird one, unfortunately most on the control has been lost so checks with GPS will be the only one.

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A Harris
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By Elbert Bassham, 

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Norman Oklahoma
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Traverse geometry like that just itches for some cross ties. Say between the 417s and the 420s.  LS adjust the lot. And RTK vectors to a few of the stations, simultaneously adjusted with the traverse data, would not hurt a bit  

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dmyhill
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Yes. You need cross ties. 

I think the guys name was Hazelton who gave a presentation on how a control traverse almost exactly like the one shown created a huge headache and cost a lot of money to fix (and even more for the lawyers). 

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