Reading the Satellite Info Screen
Most GPS devices come with a screen that is referred to as the Satellite Info page where you can see the details and reception of individual satellites. So what is this screen telling you, and how do you interpret the data? We will help you navigate this mysterious information.
Let’s jump right in and take a look at this satellite info screen from a Garmin Nuvi. At the top right corner is your location. I’ve removed the coordinates in these examples, but it will show you your current latitude and longitude. Under that is your speed and current elevation, hopefully self explanatory. Under that is where things get interesting. All of the vertical bars correspond to a satellite that the GPS is listening to. The numbers at the bottom refer to a specific satellite number. Here the GPS is listening to 2, 4, 5, 10, 12, 13, 17, 20, 23, and 30. Note that most of the bars are blue. On this GPS that means that the GPS is listening to that satellite and the information being received is good enough to be able to use in the calculation of your current position.
Sometimes you might see a “hollow” bar or a slot for a bar but no bar itself. This is the case with satellite #20. Data from that satellite is not being used to calculate your position. Taller bars indicate better data coming from that satellite. Number 30, 23, and 5 in this case are providing the best reception.
On the left side of the picture is a “map” of the satellites. Think of this as looking down at Earth (the big circle) with North at the top, and your current location centered in the circle. Now thinking of yourself centered in the middl, the outer circle represents the horizon, and the inner circle is looking up at an angle of about 45°.
Satellite #2 is to our West, a little bit North, and fairly high in the sky. (More than 45°.) Similarly, satellite number 4 is to the Northeast and also fairly high in the sky. Number 12 is just about 45° (half way from the horizon to vertical) and is to our Northwest. Number 20, which we are getting little to no reception from, is the furthest away, to the Northeast, and is just about on the horizon.
You can also see the current moon position in this view, and the current location of the sun which is about to set to the Southwest. There is also a little red dot which indicates our last calculated direction of travel.
The Garmin view provides similar data, without the sun and moon information. Here we can see the satellites the GPS is listening to, and the relative strength of those satellites. At the bottom of the each satellite bar are two numbers. The top number represents how good of a signal we are getting from that satellite. The bottom number represents the satellite number. Here you can see that we are getting the best signal from satellites number 17 and 30 with strength values of 39 and 38 respectively. Note satellite number 20 which is shown in a different gray. We can see that we are getting some data from that satellite (18), however it isn’t good enough data yet to be used in calculating our position. Again, there is a similar “sky map” to the Garmin display in the upper right.
Here is an example of a GPS which has been turned on, but hasn’t been turned on long enough yet to capture my location. The satellites it expects to find, and is listening for, are represented on the map in gray. The only two satellites it is currently listening to are number 5 and number 12. I don’t have it in this screenshot, but the DeLorme will display the satellite bars in three colors. Red if it is receiving data but that data isn’t good enough yet to be used in the determining your location. Green is used when it is using that data for a calculation, and the bars will change to blue if WAAS correction information has been received for that satellite. Again, you have the similar “sky view” showing the relative location of the satellites.
So there you have it, the GPS satellite screen demystified. Props to Garmin for having the clearest, most informative info screen.