How long to wait after the watch says "GPS is ready"?

C.sco said:

There's a big difference in accuracy between having 4 satellites locked, and having 20+ satellites.

The only problem is that this data field provided by Garmin only shows the signal strength, but not the accuracy.

These are two values that are not necessarily dependent on each other.

There are situations where a lower signal strength provides better accuracy than a higher signal strength.

I don't know just a theory. Because there is a problem with the API for visualization and green usually does not mean its ready.

KrapfenKringel said:

if you start your route as soon as the GPS gets "green" your starting point is a mess and not near your real starting point. Or is it just me?

I often go straight away and don't have any problem. However, I do tend to fire up the activity while I'm getting ready so more often than not there's an in-built delay from the green to going off.

bluefish said:

What is your explanation for an amber band when the signal is full ?

Was that directed at me, or at KK? Because it is persuasive evidence that the blue bar field is giving you 5 bars for a 2D lock, where the coloured arc is differentiating no lock, 2D lock and 3D lock. Which was my point. The green bar means more than "at least one satellite was found", rather at least four.

Better information than the blue bar field, but it's not necessarily enough for starting the activity, just because as soon as you start moving the sky view changes, and if you lose sight of one of those four the position will wander. C.sco put this really well upthread.

Yes, that was directed at you.

Ok, thanks for your explanation. But why are there five levels in the signal strength data field when there are only 2 status messages here (no signal - full signal) ?

A note : by the way, the handheld devices like the GPSmaps use all 5 fields for signal strength.

Unfortunately, the fenix only has one data field for signal strength. The data field for accuracy is missing.

I don't wait, just go.  I worry about lunch far more than a squirrelly starting point.

I just want to throw my two cents in on the subject..  As mcbadger explained, the colored bands represent the satellites your watch has acquired.  Red means 0-2, amber means you have 3 which is enough to track latitude and longitude (2D) and green means a minimum of 4 has been acquired to track latitude, longitude and altitude (3D).  Many are unaware you can have a GPS track with amber. A search in these forums will show many who have done activities with just an amber band and are surprised that had a recorded track.  The GPS signal strength graph just shows the signal strength of the satellites you're current acquired to and I would argue with mcbadger that it's just as important as the colored bands.  For example, in the photo posted by bluefish, he acquired 3 satellites good enough for a 2D track and he had good signal strength from those 3.  He very well could have had a green band with 4 bars on his signal graph meaning nothing more than he had at least 4 satellites acquired for a 3D track, but the signal from those 4 could have been better.  As you can see, they work hand in hand.  So, to answer the OP's question about how long to wait; my answer would be it depends.  C.sco brought up a great point about the more the better.  We move, satellites move and terrain may change during our route.  I live in Corpus Christi, TX.  I don't have the issue of hills, valleys, buildings or even thick vegetation.  Once I receive a green band chances are I'm just going to acquire more satellites during my activity and won't drop below 4.  I don't need to wait very long after the green band to start.  From reading previous post, I know C.sco does a lot of activities in the mountain ranges of California.  It's makes more sense for him to wait longer and acquire more satellites before he starts because the type of terrain he's in he has a greater chance of dropping satellites than I would.  Without the ability to see how many satellites we've actually acquired, I believe C.sco's advice of the longer the better is best practice.

For example, in the photo posted by bluefish, he acquired 3 satellites good enough for a 2D track

In fact, however, you need at least a fourth satellite. This is because the GPS receiver does not have an atomic clock, but a quartz clock, and the matching of the times is therefore far too inaccurate. Every thousandth deviation results in an uncertainty in the position determination of about 300 kilometers. But because the deviation is always the same, a GPS receiver can compensate for this with the information from the fourth satellite. It calculates the error using four equations with four unknowns.

Nevertheless, the radius of a determined position is still relatively large, among other things due to slight deviations of the satellites from their optimal orbits, atmospheric disturbances or signal reflections. This blurring can be alleviated by additional satellite signals, among other things. However, correction signals from geostationary satellites are also used to compensate. These are satellites that are not in orbit, but always exactly over a point on the earth and rotate with it.

I'm not saying 3 satellites is the best for recording a track.  I'm saying you only need to acquire 3 to triangulate your location using latitude and longitude.  It's not true saying a fourth is required.  You need at least a 4th to include altitude and to compensate for the error in the receivers clock.  If only 3 satellites are available, the GPS receiver can get an approximate position by making the assumption that you are at mean sea level. If you really are at mean sea level, the position will be reasonably accurate. However if you are in the mountains, the 2D fix could be hundreds of meters off. I think we all agree the more the merrier?