Don’t Get Sued. Be Redundant.

Ten seconds is all it takes to save your company.  When using GNSS, it is VERY important to take redundant shots on survey evidence.  Redundancy is used to prove the position of survey evidence land surveyors tie in or place.  Without redundancy land surveyors have no proof in court as to the actual position of survey evidence.  I have seen plenty of times when GNSS does not have a good initialization.  Taking a shot in a tree covered area or a spot near buildings can be a tedious task.  The signal from the satellites will bounce off the tree limbs and leaves or the buildings.  This is known as multipath as the signal has more than one path to the GNSS receiver.  This makes a longer distance from the satellite to the receiver.  These incorrect distances can lead to incorrect positions.  Today’s GNSS are getting better at reducing the effects of multipath.

Take a second shot on the survey evidence you tie in.  This step can be very simple or more complicated.  A simple method of redundancy is to lose initialization and then regain it.  Using this new initialization you can shoot the point a second time.  If this point is within your desired tolerance then everything is great.  If it is not within your desired tolerance then something went wrong.  You can see this in the field at the time of the survey.  A more complicated method is to take shots on your survey points once.  After you get all your points tied in re-tie the points a second time.  Usually the time period between the two shots is enough for the satellite geometry to have changed.

A redundant shot on survey evidence only takes a few seconds and can save your company.  Some surveyors only take a second long shot on evidence and call it good.  I generally take a 20 second shot, lose my initialization and take a second 20 second shot.  A twenty second shot will average the unsteadiness of the rod.  If I take my seconds shot and it doesn’t check with my first shot I will lose initialization and take a third shot.  This will usually match one of the first two shots.  Sometimes I will take more shots depending on the tree cover.

Redundancy has to be balanced with profit.  If you take it to the extremes redundancy could take a lot of time and cost a lot of money.


 

Category(s): Global Navigation Satellite System
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3 Responses to Don’t Get Sued. Be Redundant.

  1. I agree, and I have had a lot of personal experience with GNSS systems.

    I’ve on numerous occasions tied in evidence under tree cover, and had my second shot be out by up to several feet, on some rare occasions metres different from my original shot.

    Definitely good advice to follow.

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