RTK GPS, Blind Faith, Accurracy, and working in harsh environments.
GPS is a STATISTICAL measurement tool. (Think 500 gallon tank, and a 1 ounce sample.) Meaning, it uses probability. IF you set up your whole system, and let it collect for 24 hrs, then post processed, and cleaned your data, you could get real close to the truth.
Each shot is a LITTLE sample over a little period of time. Say, 3 minutes. When you work in deep woods, you add more error per shot, or, it’s like taking that little 1 ounce sample, BEFORE thoroughly mixing the 500 gallon tank.
In this post, I want to show several screen shots, taken from a recent survey.
These screen shots are turned on, in my GPS system, in case of the need for later evaluation. So, they are available for EVERY point taken by me for 5 yrs.
In this First Pic, we have Point Number 4813. The LEFT hand square shows HORIZONTAL shot spread. Kind of like shooting at a target with a shotgun. the Right hand square shows the vertical shot spread. The Star shows the RTPK shot being in agreement From RTK to RTPK is: (N-.003′ E-.013′ and Down 0.125′). The size of the left hand box is 0.203 feet, and the size of the Vertical box is 0.266 feet. This shot took a total of 6 Minutes. It is in deep dark woods. What this is saying, is that it is confident that I have that shot within 0.203 feet.
I want it more accurate than that. So, I re-shoot it.
Here is the second shot. 4814. It generates an even larger left hand square on the left, (Horizontal). It’s 0.25′. Also, RTPK and RTK disagree now by N-0.084′ E-0.073′ and Down 0.087′.
And, the difference between these shots is S26?ø48’W 0.18′, (This is from Point Number 4814 to 4813) This is shown on the box 1 up, and 1 left from the SE corner of the screen shot.
Now, this is too large of a difference for this shot.
So, I shoot it a 3rd time.
Here is the 3rd shot.
Here, we get again a large shot spread, (Left Box is 0.25′ and right box is 0.391)
However, the inverse between 4815, and 4813 is S02?ø23’51” W 0.062′. At this point, I decide to shoot it one more time.
Here is the shot:
Here is the 4th shot. Now, the box on the left is much smaller, (0.078′ Horiz. and 0.168 vert)
Inverse from the first, to this 4th shot is N 27?ø49’27″W 0.033′
I now use an average command, and it makes a coordinate that is nearly on top of 4816. It is called 4813A.
This is my final coord.
The 4 shots have taken my 11 minutes.
And, I’m done.
I did not take a pic of the area. But, it was 60′ hardwoods and pines. It’s only 5 miles from my house. If somebody asks, I’ll take pics of the area.
I felt that my happiness with the Javad system deserved an explanation.
Now, go get ready for new year!!
Nate
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