Notice that a point feature has been selected. It’s important that before you export your data file to GIS or CAD, you check the standard deviation of every point feature.
If using a 2-5 meter mapping system like a Juno3B, the number would necessarily have to be higher simply because a receiver of that type could not consistently produce more accurate results. If using a very accurate GNSS receiver, the acceptable number would probably be quite low.
It’s common for an organization to come up with a policy that dictates, possibly for a single project, what an acceptable standard deviation should be. This means that theoretically, one of the 10 positions was right on the average location, and one of the positions was 1.4 feet away from that location. From that location, it measures a distance to each of the positions in the group, and then displays the average distance.
#EXPROTING DATA FROM GPS PATHFINDER OFFICE TO CAD SOFTWARE#
If you collected 10 positions for the point feature, the software spatially averages those positions to come up with a single location. Here is how Pathfinder Office calculates that value: In other words, if you were using a Geo7X, H-Star receiver, you would want very small numbers to be revealed. The standard deviation is a precision value calculated by Pathfinder Office that reflects how closely the individual GNSS positions were able to repeat to themselves. Now, let’s look at the standard deviation of each point feature. Does it look like it’s supposed to, based on how and where you collected the data? Okay check. You open the corrected file in the Pathfinder Office Map window and check your file visually. This is ideal when selecting a base station when using a multi-constellation GNSS receiver. Let’s also assume that the base station file contained both GPS and GLONASS data with an integrity index of 80 or higher. You post process the data file with a base station close enough to your project site to achieve the rated accuracy of your field device. The first step is to perform differential correction, assuming that you did not have a real time correction source in the field. Here are some recommended steps you can go through to insure that you are exporting your best data when it comes time to send it to GIS. When you bring your data back into the office and look at it in Pathfinder Office, you notice that some of your features don’t look right. This is certainly a common environment in the Pacific Northwest and in many other areas. Let’s also say you are using a handheld GNSS mapping system with no external antenna. Let’s say you are collecting data in a moderately open area where hills and some trees are present. Short of this, there are going to be errors in your dataset, most of which you can remove before sending it to GIS or CAD. This is one in which there are no obstructions higher than the GNSS antenna and the data capture is performed perfectly by an experienced user. The only users who can almost avoid this are those who perform their field work in a completely open environment. Try as we might to setup our data collection software correctly and use a repeatable field data collection protocol to collect high accuracy data, there’s not much we can do to prevent GNSS errors from creeping into our features.
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