So now that you have a very basic understanding of how GPS positioning works, let’s dive a little deeper. We all know about handheld GPS, which could be a handheld Garmin that you have for hunting, or a SPOT emergency locating device, but most of us just think of our smartphones now. For the purpose of this article we will use smartphones to differentiate between the high accuracy GPS we use on a jobsite and Google Maps on our phone.

To keep it simple, smartphones use what they call fake GPS. The reality of phone GPS is that the location it calculates is only accurate to within 3-5m horizontally. Then the software engineers take over. In Google Maps, they have developed a feature into it that snaps your little blue dot to the nearest road while you’re driving, so that it looks like your GPS is super accurate, but in reality it’s just not. Some phones will utilize the data from the cell towers and wifi signals to help narrow down your location, but in the end it’s still a smartphone, and the antenna inside your phone that receives the satellite signals just isn’t good enough for a precise location like our rovers on site. There is a reason that our construction GPS systems cost 40k+, and this is it.

Our smartphones are also missing a big key piece of the puzzle, which is a base station. The base station serves 2 key functions to our high accuracy construction GPS. 

1. It’s a point of reference that the rover uses to compare its position to. 

2. It calculates the necessary corrections to the satellite signals to correct for any weird stuff that happens to the signal as it travels through the earth’s atmosphere.

Lets touch on the corrections that need to be made to the signal, and why it’s so important to our accurate position.

As we know, the GPS signal is a very complex message that is sent from the satellite. In order for our receiver to get all the information contained within it, and to use it to calculate an accurate position, we need to make corrections to it. As we touched on in part 1, time is a very important part of the position solution. And there’s a layer of the earth’s atmosphere, called the ionosphere, that has a bunch of stuff (ions and electrons) that delays the signal a bit. So that needs to be corrected.

Enter the base station. It’s sitting there on your tripod or your post just chillin. You went through the proper protocol to set it up on known coordinates, so it knows its exact position on your site. Now, as it’s taking in all the GPS signals, it’s calculating its own position based on that. But then it’s like, wait a minute. The GPS position I’m calculating isn’t exactly matching the control point coordinates. So then it says, if I adjust the signals a little bit, I can get it to match my coordinates really well. So if I adjust the signal from satellite 13 a little bit, and satellite 23 a little bit more, and so on for all the satellites, we got it sorted out. Then the base packages this information up, sends it out to the rover so it can make the same corrections, and voila. Accurate positioning on your job site. Piece of cake right?