Seattle Forrest

Thanks for this important correction! 🙂

gpburdell

To be clear, I didn't mean anything as a "correction" - just an added tidbit of information that doesn't really matter in the grand scheme of things.

Daniel4

Here's a question I could never find a straight answer when I google it.

Three satellites will give your location. Four satellites will give you your elevation. So why is it that I don't get my lat/long on my GPS (Garmin GPSMap 78) until it locks on five or more satellites? Many times I see my gps locked on three satellites but no lat/long reading while it's still trying to lock on two or more satellites.

Seattle Forrest

It's hard to know how much info to give when somebody asks a question with a very technical answer. I tend to give just barely enough because I don't want to confuse anyone who's trying to grasp the concept. Technically what I described wouldn't even work because knowing where each satellite is is a big part of the "magic." Between the two of us, we got this. 🙂

njkayaker

3 is enough but not all of those three will be visible together for very long. I’m guessing your GPS is picky about 5 so the location will be consistent for a longer period.

GPS isn’t considered very good for elevation. A major reason is assumptions made to make the location calculations easier/faster.

njkayaker

For this thread, indicating that GPS only provides location was enough. The “ephemera” stuff wasn’t really relevant to his question and might be confusing. (But it’s cool you knew about it. )

gpburdell

OP’s question was already thoroughly answered and the discussion was off on tangents.

If someone were to be confused by my comment, well…

Rest assured that I’ll give your guidance just as much consideration as it deserves.

Tourist in MSN

You need four satalites for a location. If the earth was a perfect sphere and airplanes did not exist, then the electronics might assume that your GPS was on the surface of the sphere and accept three satellites.

If I was an engineer at Garmin (or one of their competitors) I would want six satellites, more is for better precision and accuracy.

It is all based on complex math, the GPS has to know where each of those satellites is. They of course are moving rather quickly so it is a moving target. And the GPS has to figure out where it is based on how long it took the signal to travel from each GPS satellite to the GPS. And atmospheric conditions can change that speed that the signal passes through the atmosphere. Thus, things like WAAS were invented, but that is off topic. And as noted above, the GPS needs to have accurate data on the orbits of the satellites, as those orbits change over time. If your GPS is not getting updated info on the internet, and I suspect many if not most bike mounted GPS units are not, then it takes at least ten minutes after you turn it on and start getting good info for the GPS to update the orbit data in its memory.

I have been retired for over a decade, I am not keeping up with the latest in GPS technology. At work I used to tell people to turn on the GPS at least a half hour before they took a reading to have time to download the satellite orbit data and the people I was talking too generally did not have WAAS correction on their GPS units. I assumed about 50 feet of accuracy in horizontal coordinates. This was for data base on water resource data and plus or minus 50 feet was generally good enough for our purposes.

The GPS I use on my bike, I turn off WAAS correction, turn off Glonass data, I do this to extend battery life. Thus I am intentionally giving up some accuracy for longer run time.

Troul 

The feedback kept to the threads purpose, with minimal trajectory.

Essentially, without a data connections, it's a game of route roulette.

znomit

If you want to only route along quiet roads you just need to carry a few extra phones with you. Google is your friend here.

https://www.theguardian.com/technolo...ffic-jam-alert

Troul 

quiet would be a nice attribute to what I like to achieve, but is not necessary. I would like more reasonable accommodations for pedestrians using better logic when addressing infrastructure modernization. How are we the people suppose to become more "green" if the infrastructure is a cornfield maze full of hinderances? Much easier to move the automatic shifter to reverse out of a dead end & mash the gas pedal when sitting on an A/C cooled seat with a nice cold beverage in the cupholder.