The True Speed of your GS 500

[twocool]

Oh, Now I know why my i phone shut down yesterday when I was really pushing the GS...

I have been told, but have no way to know for sure, that the GPS in phones is not as good as stand alone GPS units........also early phones used a different system for positioning, not  gps, but position related to cell towers.....

There is lots of navigation apps for flying available for i phone or android tablets...but most pilots do not use the "internal" GPS in these devices.....but rather feed in the GPS signal from a "better" dedicated GPS unit.......


technology is moving really fast so who knows anymore.....

Cookie

Good to know the system has been upgraded and the ruskies have a system too. I know the GPS is fairly on the money I never said its so far out its bit funny but once as a laugh I used 2 GPS, 2 iPhones and reading my car speedo and found the iPhones read the same speed, the gps's gave different readings (about 4km/h difference) and that my car speedo is a bit on the conservative side which is fine by me cause I like my licence. With that info which do you believe? Which is where I base my opinion on of not fully trusting a GPS for my speeds.

Here's a fun fact. The iPhone has a built in function apparently to automatically shut down once it reaches 2.5 times the speed of sound in case it is being used as a missile guidance system. Apparently.

[Janx101]

Lol two cool .... Using hi octane again are ya? 

[twocool]

Rocket fuel...

Lol two cool .... Using hi octane again are ya? 

[twocool]

yeah...this is why a cop is not gonna cite you for 1 over the limit...it will not stand up in court....

Every time I have been stopped for speeding...guess what...I WAS speeding....almost every time the cop let me go ...(I suddenly get very polite when I get stopped)

One time however, I was driving thru South Carolina in my 1966 VW micro bus.....the state troopers has set up a speed trap, and they pulled over an entire line of about 12 cars.....I was about #6 in line..........one by one the cops worked their way back, giving out speeding tickets....when they got to me....and said I was doing 75 in a 60 zone...I said..."officer....this vehicle is incapable of going 75....the top speed is 58 MPH....you can take a ride with me and I'll show you"...the officer took a couple steps back....eyeballed my beat- o-crap van...and came back with a "warning" not a ticket.........later I discovered some slack in the accelerator cable, and was able to attain 60 MPH!


Cookie

From what I have seen of documents ..

For enforcement purposes ...

Laser 0.5 km/h accurate ,800 m scan, 600-400m usual active track range

Ka band (slant radar) , 1-3km/h accurate 150m? Scan 10-40 m usual active track range (not as popular as when they first came out.. Thankfully)

K band 2-5 km/h accurate, 500-600m scan, 300-100m usual active track range

X Band (old and clunky) 7-10km/h accurate, 300-500m scan, 350-150m usual active track range

Mk 1 police eyeball ... 'Apparently everywhere' ... 'Always accurate' ... 'See around corners and over hills?' .... Often associated in the old days ... With the police boot up the arse! 

[sledge]

Now, however, your speedo can over read by 10% (ie you can be doing 10% less than what your speedo says) but it can not over read at all. So if your speedo says 60 and you're doing 61, it's now a breach of the ADR.

Shouldn't that be `under`?

[Leadberry]

Guess the point I'm making is if a cop pulls you over for doing 1mph over the limit (he feels like being a complete c@%t this particular day) but your gps says your doing the limit. And you somehow document this, and take the ticket to court I have a feeling the judge will believe the policeman with his speed measurement device over your gps.

And as for government conspiracy it's a fact GPS was developed for the US military and they have control over the satellites. The advantage of this is if your using your gps in Iraq or Afghanistan or Pakistan or Iran (any warzone or area of US interest pretty much) your signal will be very powerful and very accurate. As for your humble gps in your car in the middle of bumfuck Arizona sure its gonna work great bouncing of at LEAST 1 satellite but personally I (and this is my opinion) wouldn't fully trust the speed it tells me I'm doing.

On my phone so this will be short.  Once again nobody said GPS was more accurate than radar.  Also we've already stated a peak error of 1 mph so you should know you could be speeding.  If you really want to get into that, most jurisdictions would never uphold a ticket for 1 mph over these days as it's too hard to hold up in court.

Second, we already acknowledged satellites are owned by DoD.  Nobody is disputing that.  Satellites are put into orbit and then they are left to drift.  We can't just fly them to a war zone.  They're overhead or they're not.  As an electrical engineer, I fail to see how this allows resolution to be selectively "very powerful" in war zones. 

The only point anyone has tried to make is that GPS speed readouts are extremely accurate.  No one claims it to be more accurate than radar or LiDAR--you're arguing with yourself there.  Your technical understanding of GPS is plain wrong. 

[MarkB]

And as for government conspiracy it's a fact GPS was developed for the US military and they have control over the satellites. The advantage of this is if your using your gps in Iraq or Afghanistan or Pakistan or Iran (any warzone or area of US interest pretty much) your signal will be very powerful and very accurate. As for your humble gps in your car in the middle of bumfuck Arizona sure its gonna work great bouncing of at LEAST 1 satellite but personally I (and this is my opinion) wouldn't fully trust the speed it tells me I'm doing.

It's also a fact that worldwide commercial aviation has become so dependent upon GPS that the US DOD would have to have an awful good reason to mess with the performance of the system anywhere on the planet.  While they are more than capable of messing with you, and by "you" I mean degrading or denying service in a specific region, there is virtually zero chance that they are or ever will outside of a war zone.

Nominal commercial grade GPS performance is generally better than about 1 m/s or about 2 MPH.  GPS performance will be degraded under difficult reception environments including dense tree cover, tall buildings, and the like.

[Soloratov]

Could switch to a digital gauge and just not worry about it. Lol...closed circuit means no outside interference. And remember, dangle tin foil from the forks and the police radar doesn't work. 

[slipperymongoose]

Guess the point I'm making is if a cop pulls you over for doing 1mph over the limit (he feels like being a complete c@%t this particular day) but your gps says your doing the limit. And you somehow document this, and take the ticket to court I have a feeling the judge will believe the policeman with his speed measurement device over your gps.

And as for government conspiracy it's a fact GPS was developed for the US military and they have control over the satellites. The advantage of this is if your using your gps in Iraq or Afghanistan or Pakistan or Iran (any warzone or area of US interest pretty much) your signal will be very powerful and very accurate. As for your humble gps in your car in the middle of bumfuck Arizona sure its gonna work great bouncing of at LEAST 1 satellite but personally I (and this is my opinion) wouldn't fully trust the speed it tells me I'm doing.

On my phone so this will be short.  Once again nobody said GPS was more accurate than radar.  Also we've already stated a peak error of 1 mph so you should know you could be speeding.  If you really want to get into that, most jurisdictions would never uphold a ticket for 1 mph over these days as it's too hard to hold up in court.

Second, we already acknowledged satellites are owned by DoD.  Nobody is disputing that.  Satellites are put into orbit and then they are left to drift.  We can't just fly them to a war zone.  They're overhead or they're not.  As an electrical engineer, I fail to see how this allows resolution to be selectively "very powerful" in war zones. 

The only point anyone has tried to make is that GPS speed readouts are extremely accurate.  No one claims it to be more accurate than radar or LiDAR--you're arguing with yourself there.  Your technical understanding of GPS is plain wrong. 

Nah my understanding of GPS is just fine thanks the entire time you missed my point of saying in my opinion I don't trust the speed readings of GPS. Aaaaand at least in the early days of the system the satellites orbit could be changed so there was always a more powerful signal over war zones for help the yanks out. Nowadays with the Russians having their system plus the American system the coverage over the earth is probably decent enough to let them float.

And here's a question for ya mr electrical engineer. If the GPS is that good why havnt car manufactures replaced speedos in cars with ones that read from GPS instead of traditional ways?

[Slack]

And here's a question for ya mr electrical engineer. If the GPS is that good why havnt car manufactures replaced speedos in cars with ones that read from GPS instead of traditional ways?

Because they only work in the plains.  As soon as your on a hill, up or down, your traveling the hypotenuse of the angle while the GPS is only calculating for the adjacent distance.  Plus the fact that it doesn't work in the mountains.

[slipperymongoose]

Good enough for me.

[Toiletbooger]

Satellites are put into orbit and then they are left to drift.  We can't just fly them to a war zone.  They're overhead or they're not.  As an electrical engineer, I fail to see how this allows resolution to be selectively "very powerful" in war zones.

I read that they can move the orbit of the gps, so conceivably they could be moved to better cover a warzone  - however as you mentioned there's still the problem that it will only pass directly overhead once every 12 or so hours. (The geography of the land would determine the actual time for line of site between the satellite and the "warzone")

In any case the current system on average has line of site to 9 satellites from any point on earth; even if they did shift a satellite, I doubt there would be any benefit to having 10 satellites overhead instead of 9.

As for the military's higher resolution, I've heard before and wikipedia agrees that the military gets better GPS resolution by using robust military equipment which runs off a separate, encrypted signal to the civilian signal. Which from a conspiracy theorist's point of view means yes, the US military could* turn off GPS for everybody but themselves (and whoever can crack the encryption).

*probably won't

[twocool]

You are not gonna drive a GS500 on a hill steep enough to make any noticeable difference....

Some GPS can measure in three dimension....Auto type usually just project your position on a conceptual surface of the earth, ignoring the ups and downs......but again still extremely accurate since we can't (or don't) ride up a grade of more than about 6%..


No matter how suspicious you are...GPS is still extremely accurate..........

Car speedos are (can be) very accurate too..........

I had an electronic speedo on my honda elite scooter 1984.......also had a gps on it...both read exaclty the same at all times......

Aviation has gone for GPS in a really big way...I guess the auto makers are still a bit behind.....

If I ever get around to building the Bobber I have in mind...the only instrument on it will be the smallest GPS I can find.......no tach, no speedo, no indicator lights etc....

Cookie

And here's a question for ya mr electrical engineer. If the GPS is that good why havnt car manufactures replaced speedos in cars with ones that read from GPS instead of traditional ways?

Because they only work in the plains.  As soon as your on a hill, up or down, your traveling the hypotenuse of the angle while the GPS is only calculating for the adjacent distance.  Plus the fact that it doesn't work in the mountains.

[slipperymongoose]

You are not gonna drive a GS500 on a hill steep enough to make any noticeable difference....

Some GPS can measure in three dimension....Auto type usually just project your position on a conceptual surface of the earth, ignoring the ups and downs......but again still extremely accurate since we can't (or don't) ride up a grade of more than about 6%..


No matter how suspicious you are...GPS is still extremely accurate..........

Car speedos are (can be) very accurate too..........

I had an electronic speedo on my honda elite scooter 1984.......also had a gps on it...both read exaclty the same at all times......

Aviation has gone for GPS in a really big way...I guess the auto makers are still a bit behind.....

If I ever get around to building the Bobber I have in mind...the only instrument on it will be the smallest GPS I can find.......no tach, no speedo, no indicator lights etc....

Cookie

And here's a question for ya mr electrical engineer. If the GPS is that good why havnt car manufactures replaced speedos in cars with ones that read from GPS instead of traditional ways?

Because they only work in the plains.  As soon as your on a hill, up or down, your traveling the hypotenuse of the angle while the GPS is only calculating for the adjacent distance.  Plus the fact that it doesn't work in the mountains.

No doubts about the benefits of GPS. When john cleese my satnav voice tells me to turn left in 300m his bang on or just about. I love having the odd satnav race to. But since doing my gps comparrasion I take the speed readouts with a grain of salt.

[BrianRC]

I would love to add my two cents here as a road rally competitor (in cars) I have seen a huge difference in the various speed measurement instruments available. I drive an older car that uses a mechanical cable driven input from the gearbox and it is fairly accurate..up to 35mph, after that you start to get slippage of the gears  (spinning on the input shafts) on the inside of the speedometer. Some are better than others but they all have a deviation.

The international standard regarding how much vehicle speeds can be off was put into effect in the late 80's if I remember correctly (65 on my 1983 car speedo is closer to 70 actual) so I missed out on that by a few years. GPS is accurate speed and distance wise only if you are traveling in a fairly straight line without any quick direction changes (switchbacks anyone?  , those can alter readings by a few 10ths of a mile and momentarily throw speed readings. GPS also suffers from line of sight signal reception issues, if you are in the mountains and there are no satellites directly above, you loose signal accuracy and it starts to guess on your speed and direction based on last known direction and speed; or it cuts out entirely. 

I use a purpose made rally computer that reads pulses off the hub of an un-driven wheel of my car and they display speed to a 10th and distance down to the 100th of a mile (or km if you like). It still can be thrown off by wheel slip of course but it is the answer to GPS inaccuracy and can easily be tuned for different wheel and tire sizes. 
I think for all intents and purposes a dedicated Gps more than fits the average riders needs.

[Janx101]

I would love to add my two cents here as a road rally competitor (in cars)



I use a purpose made rally computer that reads pulses off the hub of an un-driven wheel of my car and they display speed to a 10th and distance down to the 100th of a mile (or km if you like)..

Yes please do!! .. rally!!! 

....  ... want that puter!!! ... 

[peterscotts]

I would love to add my two cents here as a road rally competitor (in cars) I have seen a huge difference in the various speed measurement instruments available.

f%$k what have I started here...

The GPS is useless once your in a tunnel which are in the major cities (looses satellite) also not much good in major cities as in the heart of the city because of all the tall building... Again looses the satellite. 

[slipperymongoose]

You got a beauty here havnt had this much fun since the last fuel oil thread

[peterscotts]

You got a beauty here havnt had this much fun since the last fuel oil thread

           

[peteGS]

Now, however, your speedo can over read by 10% (ie you can be doing 10% less than what your speedo says) but it can not over read at all. So if your speedo says 60 and you're doing 61, it's now a breach of the ADR.

Shouldn't that be `under`?

Yup! Brain fart right there! Nothing like contradicting one's self in the same sentence...