Forerunner 735 vs 935

[Showtime]

Very similar experience to my wife's Garmin.

Bought it a month ago and the first unit had no firmware loaded out of the box! was really annoyed because it was a birthday present.

Replacement unit is constantly losing connection to her phone and smart notifications dont come through until she manually connects it again.

 

The bluetooth connection has a really short range too, compared to my Suunto which gets alerts all over the house regardless of where my phone is, hers stops working after about 3 meters.

 

Yes the Bluetooth range is also crazy short.

 

And this is from the latest 945 5.40 / 5.50 firmware update release notes:

 

- Fix an iOS reconnection issue on some phones

 

So it's a known problem for them. Except the new firmware didn't change anything for me.

[New Landy new life]

My phone was in the gym locker and walked down a set of stairs to the pool and the watch picked up a phone call.

Go figure [emoji2371]

[LBKloppers]

I don't think you're accurate with this statement. GPS positioning uses moving satellites. Each of those transmit a timing signal. Your GPS chip - whether it is a cycling computer or a wrist worn watch have to calculate the position combining the timing transmissions from each of those transmissions received. there is quite a bit of calculation necessary and the relativity theory plays a rather big role, but the mere fact that the satellites are moving and its transmission spreads over the horizon means whatever unit you're using can calculate the elevation. 

Consider for a moment the owners of GPS. GPS is owned by the United States Air-force and the GPS was developed as a tool to guide their missiles. Do you for one moment think they are only going to fire missiles in areas with good maps? No. What they do is the limit the ability of the software to calculate too accurately. For a fee, some (Geologist for example) may buy the accuracy upgrade, but you will never be able to use GPS against critical US facilities. I can only guess that Russia does the same. 

 

Problem is that watches etc. don't use GPS to determine altitude (something that GPS is notoriously bad at btw). They use GPS to determine position and then survey maps to determine altitude at said position. So in that case your elevation gain is actually based on how accurate the surveyed elevations are in the area that you are riding (and how accurately the GPS is locating you on said surveyed maps) which is also not a given.

 

Both approaches have their pros and cons.

[PSYCHOsmurfZA]

Sheez, wish I knew someone with that kind of discount

I got my Garmin through my brother in law with his multiply at 40% off best thing in the world!

[DieselnDust]

I don't think you're accurate with this statement. GPS positioning uses moving satellites. Each of those transmit a timing signal. Your GPS chip - whether it is a cycling computer or a wrist worn watch have to calculate the position combining the timing transmissions from each of those transmissions received. there is quite a bit of calculation necessary and the relativity theory plays a rather big role, but the mere fact that the satellites are moving and its transmission spreads over the horizon means whatever unit you're using can calculate the elevation. 

Consider for a moment the owners of GPS. GPS is owned by the United States Air-force and the GPS was developed as a tool to guide their missiles. Do you for one moment think they are only going to fire missiles in areas with good maps? No. What they do is the limit the ability of the software to calculate too accurately. For a fee, some (Geologist for example) may buy the accuracy upgrade, but you will never be able to use GPS against critical US facilities. I can only guess that Russia does the same. 

 

 

spot on!

[Jehosefat]

I don't think you're accurate with this statement. GPS positioning uses moving satellites. Each of those transmit a timing signal. Your GPS chip - whether it is a cycling computer or a wrist worn watch have to calculate the position combining the timing transmissions from each of those transmissions received. there is quite a bit of calculation necessary and the relativity theory plays a rather big role, but the mere fact that the satellites are moving and its transmission spreads over the horizon means whatever unit you're using can calculate the elevation. 

Consider for a moment the owners of GPS. GPS is owned by the United States Air-force and the GPS was developed as a tool to guide their missiles. Do you for one moment think they are only going to fire missiles in areas with good maps? No. What they do is the limit the ability of the software to calculate too accurately. For a fee, some (Geologist for example) may buy the accuracy upgrade, but you will never be able to use GPS against critical US facilities. I can only guess that Russia does the same. 

 

I can almost guarantee that the missiles that they are firing will not be using the GPS to calculate their altitude. Historically the lower accuracy on non-military GPS units was due to them connecting to a different transmission from the satellites (known as selective availability). This is now generally switched off but they (the US) can (and do) switch it on again at any time in certain areas (usually conflict areas so the enemy can't use the system). It is not, as per your post, something you can "buy the accuracy upgrade" to avoid.

 

Yes, GPS can estimate your altitude but the estimation error is 3 - 4 times higher than it's estimation error in terms of horizontal position (partially because any software that uses GPS has to make assumptions about the shape of the earth which is never exact as well as because of how the satellites are arranged and the altitudes of their orbits). In addition to this, most sports GPS units are designed for power efficiency rather than absolute accuracy so you will find much higher estimation errors on them than on (as per your example) missiles.

 

 

So, your GPS unit knows where the satellites are at any given time; it knows where it is (by triangulation); and it needs to tell you where you are relative to its model (which is selectable) of the Earth’s surface.

Your GPS unit has multiple models (datums) of the Earth in its memory.

The most commonly recognised global model is the World Geodetic System established in 1984 (WGS84). There are other datums that may be more accurate for individual countries, but in the hang and paragliding world we tend to use WGS84.

WGS84 defines the Earth as an ellipsoid: a squashed ball. This ellipsoid is a pretty good approximation to the mean sea level around the planet, but is recognised as having errors of between -100 m and +70 m with respect to the geoid, depending where you are on the planet.

Edited December 8, 2020 by Jehosefat

[DieselnDust]

missile guidance systems certainly do use GPS to establish altitude accurately.

Aircraft use a downward looking RADAR unless its a stealth design like the F-117 or F-22, Su-57 then it will use a combination of sensors including IR

[LBKloppers]

I am not going into the technicalities here suffice to say that GPS does NOT need maps for elevation. And while I disagree with the need for barometric elevation measurement, my experience lead me to favor a GPS elevation. It repeats and it doesn't drop me below sea level.

I can almost guarantee that the missiles that they are firing will not be using the GPS to calculate their altitude. Historically the lower accuracy on non-military GPS units was due to them connecting to a different transmission from the satellites (known as selective availability). This is now generally switched off but they (the US) can (and do) switch it on again at any time in certain areas (usually conflict areas so the enemy can't use the system). It is not, as per your post, something you can "buy the accuracy upgrade" to avoid.

 

Yes, GPS can estimate your altitude but the estimation error is 3 - 4 times higher than it's estimation error in terms of horizontal position (partially because any software that uses GPS has to make assumptions about the shape of the earth which is never exact as well as because of how the satellites are arranged and the altitudes of their orbits). In addition to this, most sports GPS units are designed for power efficiency rather than absolute accuracy so you will find much higher estimation errors on them than on (as per your example) missiles.

[GhostSixFour]

I am not going into the technicalities here suffice to say that GPS does NOT need maps for elevation. And while I disagree with the need for barometric elevation measurement, my experience lead me to favor a GPS elevation. It repeats and it doesn't drop me below sea level.

The wikipedia article for Altimeter is quite interesting:

https://en.wikipedia.org/wiki/Altimeter

 

 

A barometric altimeter, used along with a topographic map, can help to verify one's location. It is more reliable, and often more accurate, than a GPS receiver for measuring altitude; the GPS signal may be unavailable, for example, when one is deep in a canyon, or it may give wildly inaccurate altitudes when all available satellites are near the horizon. Because barometric pressure changes with the weather, hikers must periodically re-calibrate their altimeters when they reach a known altitude, such as a trail junction or peak marked on a topographical map.

 

and

 

 

Global Positioning System (GPS) receivers can also determine altitude by trilateration with four or more satellites. In aircraft, altitude determined using autonomous GPS is not reliable enough to supersede the pressure altimeter without using some method of augmentation.^[9] In hiking and climbing, it is common to find that the altitude measured by GPS is off by as much as 400 feet (122 metres) depending on satellite orientation.

 

So your experience is not the experience of the majority it seems. Or you've been lucky in terms of satellite positioning when going out on exercises.

[Jehosefat]

I am not going into the technicalities here suffice to say that GPS does NOT need maps for elevation. And while I disagree with the need for barometric elevation measurement, my experience lead me to favor a GPS elevation. It repeats and it doesn't drop me below sea level.

Please do go into detail though, I'm very interested in how that would work. Yes, theoretically a GPS unit can get a pretty accurate 3 dimensional location for itself (under ideal conditions) but how would would it know how far that location is above sea level without either a model of the globe or a map?

[Jehosefat]

missile guidance systems certainly do use GPS to establish altitude accurately.

Aircraft use a downward looking RADAR unless its a stealth design like the F-117 or F-22, Su-57 then it will use a combination of sensors including IR

If you are referring to cruise missiles (which are the only ones that really need location guidance) then they also use radar for above ground level altitude (it's usually tied into their terrain following radar system).

 

In either case, radar altimeters give altitude above ground level which for cycling would not be useful at all (because your GPS unit would pretty much always be approx. 1m AGL). In order to translate AGL altitude to ASL altitude you still need either a topographical map or a model of the globe.

[LBKloppers]

Jehosefat, I am not a teacher or even a writer of sorts, but I'll try.

Imagine a tennis ball covered in soap bubbles of the same size, but they do not deform like real bubbles. They each must have a nice round sphere. These spheres will overlap each other. Lets say the bubbles are 32 in number just like the GPS number of satellites above our heads. If you can picture this, you're halfway there. You may now position yourself anywhere on the tennis ball and at any elevation within this sphere of bubbles and you will intersect different bubbles at different angles and distances and because at at specific time there are about 11 satellites over our heads, there are way more than the minimum 3 to determine your x, y and z axis's.

If you have ever seen how the old school method to develop topographical maps from aerial photos by just using a couple of lenses looking at one point but at different angles, you might start to get the idea. Its just now done on the fly using electromagnetic radiation and calculated by electronics, but it boils down to the same thing.

Remember GPS satellites are not geostationary and the receiver of the GPS signal need to use the relativity theory to calculate approaching or departure speeds. Some satellites visible to your device are at relative angles from you due to the curvature of the earth. It takes quite a bit of calculation and one of the reasons a GPS device uses so much more battery power than a normal watch would do.

 

Also remember the entire discussion started with the need to have a barometric measurement on your GPS devise. If you're a pilot you get the actual local barometric readings from the local weatherman. That allows the pilot to make the adjustment to his instruments (correct me if I am wrong, but the pilot does not make this adjustment to the GPS) in order for the instrument to display correctly. As the pilot flies to his new destination, he will get the updates as necessary. A cyclist does not have that. The weather can change in the time since he started on his ride. There in no way the device can know or measure that the reference barometric pressure has changed and on the cycling device, the cyclist do not have the ability the determine nor adjust for the changes as it happens.

 

You also keep asking about cruise missiles. If what you're saying is true (the necessity of maps), then the USA need to have very detailed geographic maps of the whole earth. It my be 2020, but I can guarantee that is not the case. There are a number of tools they use to guide those missiles to its destination. Star positioning, gyroscopic compasses, Radar in various forms and frequencies, Laser in looking forward, looking down, weather and even some remote adjustments from the launch controllers on the fly. Often there will be team who can light up a target using portable lasers or if that is not possible they do that with military satellites. Many options and all of those contributing to the costs to develop and run these machines. Not many countries can afford that and its my guess that the exclusivity of the entire package lead to the global availability of GPS in limited accuracy, because GPS on its own is not enough to do the kind of harm a country like the US fears.

[Showtime]

Just an update. I changed from the iPhone XR to an S20 and the 945 hasn't missed a beat since.

 

Not necessarily an Apple problem, could be an isolated Garmin Connect IOS problem but regardless my watch is working as expected now.

 

My experience has been a bit different.

 

My first 945 had to be replaced due to a hardware fault causing the entire sensor stack to stop working. It took forever to get a replacement but 2020 so I was patient.

 

My current one I can't get to stay connected to the phone no matter what. I've repeated all the suggestions, restart phone, restart watch, unpair, pair etc but if I move to a different room it doesn't connect again until I restart the app and sometimes the bluetooth connection as well. Used my old 735 last week and no problems.

 

I almost don't have the energy to return again but it's a pricy item not to be working 100%.

[Jehosefat]

Jehosefat, I am not a teacher or even a writer of sorts, but I'll try.

Imagine a tennis ball covered in soap bubbles of the same size, but they do not deform like real bubbles. They each must have a nice round sphere. These spheres will overlap each other. Lets say the bubbles are 32 in number just like the GPS number of satellites above our heads. If you can picture this, you're halfway there. You may now position yourself anywhere on the tennis ball and at any elevation within this sphere of bubbles and you will intersect different bubbles at different angles and distances and because at at specific time there are about 11 satellites over our heads, there are way more than the minimum 3 to determine your x, y and z axis's.

If you have ever seen how the old school method to develop topographical maps from aerial photos by just using a couple of lenses looking at one point but at different angles, you might start to get the idea. Its just now done on the fly using electromagnetic radiation and calculated by electronics, but it boils down to the same thing.

Remember GPS satellites are not geostationary and the receiver of the GPS signal need to use the relativity theory to calculate approaching or departure speeds. Some satellites visible to your device are at relative angles from you due to the curvature of the earth. It takes quite a bit of calculation and one of the reasons a GPS device uses so much more battery power than a normal watch would do.

 

Also remember the entire discussion started with the need to have a barometric measurement on your GPS devise. If you're a pilot you get the actual local barometric readings from the local weatherman. That allows the pilot to make the adjustment to his instruments (correct me if I am wrong, but the pilot does not make this adjustment to the GPS) in order for the instrument to display correctly. As the pilot flies to his new destination, he will get the updates as necessary. A cyclist does not have that. The weather can change in the time since he started on his ride. There in no way the device can know or measure that the reference barometric pressure has changed and on the cycling device, the cyclist do not have the ability the determine nor adjust for the changes as it happens.

 

You also keep asking about cruise missiles. If what you're saying is true (the necessity of maps), then the USA need to have very detailed geographic maps of the whole earth. It my be 2020, but I can guarantee that is not the case. There are a number of tools they use to guide those missiles to its destination. Star positioning, gyroscopic compasses, Radar in various forms and frequencies, Laser in looking forward, looking down, weather and even some remote adjustments from the launch controllers on the fly. Often there will be team who can light up a target using portable lasers or if that is not possible they do that with military satellites. Many options and all of those contributing to the costs to develop and run these machines. Not many countries can afford that and its my guess that the exclusivity of the entire package lead to the global availability of GPS in limited accuracy, because GPS on its own is not enough to do the kind of harm a country like the US fears.

 

I am well aware of how the GPS system works, I have a degree in applied maths and have done a project on the calculations and error correction in the system as part of said degree. You have still not answered my question as to how the GPS receiver would know how far it is above sea level without either a model of the earth or a map.

 

I agree that using GPS can give you a pretty accurate position in space (in particular, relative to the gravitational center of the planet that all the satellites orbit). This can also be limited by line-of-sight issues due to mountains, buildings, etc. but sure, lets assume an ideal signal scenario. But knowing your position relative to the center of the earth is not the same as knowing your height above sea level (since that differs, potentially quite substantially, across the globe).

 

Secondly, I never said that barometric pressure was a perfect option for measuring altitude, just that it was better/more accurate than GPS. Which has been backed up by pretty much all the research and links that have been posted here.

 

You brought up the missiles first, I was just responding to the points made by yourself and DieselnDust. I never said that the missiles can only be fired into areas with high quality maps, all I said is that for missiles that are very sensitive to altitude (in particular cruise missiles with terrain-following features) GPS is not accurate enough to be used for altitude measurement and other methods are used, many of which you listed.

Edited January 6, 2021 by Jehosefat