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Carlson SurvNET GPS Adjustment  

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NeilRick
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We recently did a survey through a Base/Rover procedure using a localization on two state place coordinates.  Then went through the adjustment process in SurvNET through Carlson Survey and adjusted the closure.  After realizing we had left out some road shots, we went back and shot in the road using the State Plane Mifi system without the Base set up.  When I dropped in the coordinates in Carlson there is an offset jag where the two road shots should meet, about 6 foot.  Is this because we used the Base on one set up and the Mifi on another?  Shouldn't it all be tied into the State Place coordinates anyways, or was there an error in our process?  Any one have any experience with this?

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James W Johnston
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It relates to the old "precise vs accurate" consideration.

If the base in the base rover combination was properly localized to the mi fi points  than your base/rover measurements should be reasonably precise because of the short baseline, but not highly accurate because they are based on two points with a longer baseline.  It's not reasonable to see a 6 foot residual.

But if you used "here" or an averaging method to determine the base position the base/rover points will only be as accurate as if you have set up a single GPS receiver...about 10 to 15 feet.  But precise within the overall network.  A residual of 6 feet would be reasonable if comparing to the mi-fi points.  It would be a consistent residual over the whole network.

When you described your procedure...shooting two points with mi-fi, then localizing the base/rover points to those two points and continuing the survey, it sounded like you were doing the right thing.

 

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MightyMoe
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Two state plane coordinates? From where did you obtain them?

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NeilRick
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We located with state plane using a wifi connection and mifi set up in our state.  We were tied into the local state plane and shot the GPS coordinates with the mobile Rover.  We shot each point twice and averaged the points.

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Dave Karoly
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Did you press "here" for your Base position on the first survey?

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NeilRick
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When we set up the base it was not over a known point.  We shot in the base using satellites.  We then localized on the two mifi coordinates we had set.

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Bill93
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I guess I posted on the wrong duplicate thread.

Did you use a Combined Scale Factor to scale your total station distance measurements to state plane?  Failing to do that will give serious residuals in most areas.

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NeilRick
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We didn't use the total station in this survey, only GPS.  I know, confusing, two posts.  Two different jobs.  The other post is about the combination of the total station and GPS files.  I replied to that post.

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Norman Oklahoma
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You are being asked about the source of your base position because 6 feet is a typical distance between an autonomous position and a corrected one. And even if your base position is correct, rover positions that are not "fixed", and are therefore autonomous, may be recorded.  Another possible source of error is a mixup with international foot / US Survey Foot settings.  

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