Data - Location, Temperature, 4G Internet ([, Camera?]) ([, OBD?])

@davee Darn, this is yet another case of me saying one thing that really means something else. Yes, the last known fix is saved, that is done to save battery. I think some are fancy enough to have motion sensors so when not moving it turns off the GPS and simply stores the resume point so to speak. I will bet my iPhone does that.

@davee Isn't this a reason for both our countries to declare a day, nay a week of national celebration? Possibly the first since WWII.

I think we are 'on the same page'! An event worth celebrating!!

Hi Ron @zander,

  I just updated my last reply ... and now see another two messages have crossed in the post.

  I don't know if any phones try to guess whether they are stationary, and hence don't need a new fix.

However, from a basic physics viewpoint, that might be tricky. It is easy for the phone to detect an acceleration, but moving at a constant speed in the same direction is 'undetectable' without extra 'clues'. Obviously, looking out of train window in daylight, would provide a clue, but in complete darkness, and no obvious noises, this becomes a challenge. And in principle, if the device could 'ensure' it was stationary, then achieving a velocity would include an acceleration phase, but integrating that accurately enough for a long period of constant velocity would usually be impracticable.

This is the same problem that pilots suffer from when flying entirely by their instruments. When the plane is in 'difficult' circumstances, the natural feelings of acceleration, etc. that humans rely on can be at odds with what the instruments are saying, and they are then conflicted between the instruments and their 'intuition'. In recent years, hopefully, GPS and the like have effectively provided an extra level of instrumentation to overcome this problem.

Best wishes, Dave

PS I maybe aging rapidly, but luckily for me, I missed WWII, so perhaps a National celebration is a little OTT!

@davee I once had an app that listed all the sensors in my phone at that time. It was more than what I thought, and I suspect it is even more. I know for instance my iPhone has a magnetic sensor that is sensitive to magnetic fields of less than 100 microgauss. My point is your ability to hold a phone motionless is extremely unlikely.

I am not sure how or if this discussion is helping the OP.

I think my concern of resynching with 4 satellites is a lot easier today with 4 or 5 GPS systems vs the one I was remembering.

Based on this new info I withdraw my concern re GPS startup time.

Hi Ron @zander,

  Holding a phone 'motionless' is improbable, but mounted, albeit maybe temporarily, as I do in my car when driving, is feasible. British roads and my 'low cost' car would preclude it having a problem, but mounted in a more luxurious vehicle, driving along a long well-maintained straight road might be a different matter.

As I said, I don't know if any phones do power down their GPS ... I am only suggesting there are practical issues to solve ... not predicting whether they have been overcome.

Best wishes, Dave

@davee Any movement through the earth's magnetic field is enough to determine movement plus the acceleration/gyroscope sensors and possibly a few more would let the phone know it is moving.

EDIT: I just found out my phone also has Lidar.

Hi Ron @zander,

   Acceleration sensors measure acceleration ... 'true' constant velocity situations are 'invisible' to them.

  Gyroscopes and magnetic sensors will pick up significant rotations. Rotation causing a change of direction is no longer a constant velocity.

Movement through Earth's magnetic field ... e.g. moving along a path of constant latitude will change the direction of the magnetic field, but unless you are very close to one of the magnetic poles, you will need to travel a long way to change the angle by even a 1/10th of a degree, which I would guess would be about the best resolution of magnetic field direction available in a commodity product like a phone.

As I have said before, I do not deny it is possible a phone could power down its GNSS/GPS when it doesn't think it is moving, as it is difficult to produce a situation where the phone is moving, but not being accelerated, if only by vibrations, etc., but I would not recommend adopting it in a product like an Apple phone without doing a lot of experiments. Of course, Apple (or Google/Android) has the resources to do such testing, if they thought it beneficial.

This is an interesting 'thought experiment', but I suspect we have exhausted the productive gains for pursuing it further. Maybe time to find a new discussion?

Best wishes, Dave

@davee Yes we have beat this to death, but the magnetic field is NOT a straight line, it is evermoving and highly erratic. The iPhone sensor is EXTREMLY sensitive (sensitive to less than 0.01 microtesla) so I am quite confident that no matter how still you thought the phone was the phone can detect the changing field. Obviously they 'map' those values to something more coarse in order to turn off the display (on more modern phones) below a certain threshold of 'movement'.

It looks like the whole discussion is moot as the OP will be using the car battery as the power source. Since the GPS board he will likely use is the one I posted then we know it has a battery to backup the memory where the last fix is stored and that battery can last more than long enough before it gets recharged by the car battery therefore problem solved!