Have you ever had a point show up in your survey database and it wasn’t where you thought it should be? Perhaps upon further examination you find that the point was located twice in the field and the survey database is reporting the first location from the raw data file. Today, we’re going to look at two things – the “why” and the “how” – why does this happen, and “how” do I fix it?
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First of all, the scenario that we will be looking at today – you have to know the problem before you can replicate it, right? I’m starting out in my data collector (TDS Survey Pro) with two points. Here are their stats:
I am going to set up on point 1, backsight point 2, and turn an angle of 90 degrees to the right for a distance of 500.00 feet and store point 3. After that, I am going to overwrite point 3 by turning an angle right of 270 degrees for a distance of 500.00 feet. This should provide us with a very obvious test case for this post.
If you take a look at the FBK created from the raw data, you will see that point 3 exists in the FBK twice – the FBK format doesn’t happen to have any provisions for deleted points.
NEZ 1 5000.0000 5000.0000 100.0000 “CONTROL1”
NEZ 2 5200.0000 5000.0000 100.0000 “CONTROL2”
! Foresight Target:My Prism, HR:5.0 (5.0 + 0.0 Offset), Prism Const.:0.0mm
STN 1 5.000 “CONTROL1”
! HR:5.0 (5.0 + 0.0 Offset)
AZ 1 2 0.00000
BS 2 0.00000
! Backsight HR:5.0 (5.0 + 0.0 Offset), Prism Const.:0.0mm
! BS check 1 – 2:ZE90.0000,SD200.0,HD err= 0.0, VD err= 0.0
! BS Circle check : angular err= 0.0000
F1 VA 3 90.00000 500.000 90.00000 “SIDESHOT”
F1 VA 3 270.00000 500.000 90.00000 “SIDESHOT”
So with these settings, what happens when we import the file into the survey database? First, we have to take a look at the settings of the database and set up a few parameters before we import the FBK into the network. These settings can be seen below:
The error tolerance area of the Survey Database Settings is very important to set up – it not only detects blunders, but can help us fix this issue with the FBK file not picking up on the deleted points. Hey, I can prove I deleted the points – see the raw data in TDS Survey Link below:
OK, admittedly, I got a bit overzealous in my point creation and initially shot point 4 instead of point 3. This should be interesting. Point 4 should not be in the project at all, and was deleted entirely in the data collector.
Now, let’s see what happens when I import the FBK file. Remember, the first point 3 that I located was to the east of point 1 and the second one was to the west of point 1. Which one came into the drawing?
Hmmm, not what we wanted, was it? Even worse, what if more points had been located from point 3? This could be a pretty significant problem if not found. But how do we find it? If I take a quick glance at all of my setups and observations, I can find out what the problem is in quick order:
The error icon in the observation will alert us to any points outside of the tolerances set. You can see that the coordinate error and the angular error are outside of the normal limits. The thing that needs to be recognized is that this is the GOOD point, not the bad point. So I know that I can right click on the first observation and delete it, which will make the second observation “good” in the survey database.
A quick update of the network, and of the points in the database, and you’ll see what happens:
Just be aware of your database, and it wouldn’t be a bad idea to just run over the data beforehand to check and see if there are any errors.