Why GPS without inertial navigation fails.

justICE · 09-05-2004, 05:11 PM

Hi,
I am new to the boards and I didn't do a search so if I am repeating something that has already been said then too bad!

Anyhow, I have seen a few posts here questioning why their car appears off the road and/or "behind" your actual position. Most times this is not due to software. Commercial GPS is inharently inaccurate. Years ago position data was intentionally false so that private users--or other governments--could not utilize governments new toy against them. The Government has since inacted a bill that removed that false position information; however, commercial applications are only offered a single datastream from satellites and are restricted by the laws of physics for the data rate and any obstructions blocking your receiver from the satellites.

Government codes allow for 2 data streams,--commercial and coded--which significantly increases the accuracy of the position data yet for their needs is still unsufficient. The solution is to take Inertial navigation--gyros are very accurate relative to a specific position--and blend it with GPS. With this system you can get down to very specific positions.

This accuracy of this system is magnitudes better in poor (and good) whether and when the ionosphere is at its peak width around 1-3pm--ever notice your positions get worse around this time? The increased accuracy in this system is caused by the fact that the blended solution is still heavily influenced by an accurate inertial system even though the GPS may be off 50-100 feet.

I guess what I am suggesting is that if you really want a good navigation system go look for something that blends inertial navigation with GPS. I am not sure if there are any commercial applications--something that would easily plug into your computer--but I have to believe they are available. I know infiniti uses a blended solution in their navigation.

--JustICE

JC-S60 · 09-05-2004, 05:29 PM

Well, that is the one thing PC-GPS solutions lack, compared to traditional in-car navigation systems (VDO, Blaupunkt, Pioneer etc...): linking to a gyro AND the tacho of your car.

The problem is with software, which takes nmea input and doesn't take anything else (as far as I know).

A solution could be to write a piece of software that takes these 3 inputs (GPS, tacho and gyro) and calculates a new, more accurate nmea stream...

Any volunteers?

lookinco · 09-05-2004, 06:29 PM

I have a Pioneer navigation right now planning to go headless and use the computer with GPS for Navi. Will I notice a big difference ? What kind of problem will I face ?

xBrady · 09-05-2004, 06:33 PM

Is this really that big of an issue for you guys? Mine rarely reports inaccurately.

pip · 09-05-2004, 06:42 PM

There used to be a major difference between military and civilian use of GPS but not now. I understand the deliberate degradation of accuraccy for civilian use was dropped. GPS is accurate to a few yards or better with 4 or more birds locked.

People see themselves off the road...its not the GPS...its the map.

jcdillin · 09-05-2004, 07:09 PM

Quote: Originally Posted by pip

There used to be a major difference between military and civilian use of GPS but not now. I understand the deliberate degradation of accuraccy for civilian use was dropped. GPS is accurate to a few yards or better with 4 or more birds locked.

People see themselves off the road...its not the GPS...its the map.

and then WAAS was supposed to improve the accuracy above and beyond that. I never have a problem with routis but I am also using it with garmin handheld gps so it could be the receiver as well.

Laidback · 09-06-2004, 04:23 AM

Quote: Originally Posted by pip

There used to be a major difference between military and civilian use of GPS but not now. I understand the deliberate degradation of accuraccy for civilian use was dropped. GPS is accurate to a few yards or better with 4 or more birds locked.

And some software has the 'snap to road' feature, which keeps you on the road as well. I find mine pretty accurate!

EBFoxbat · 09-06-2004, 09:02 AM

Military GPS is accurate to wihin 3 feet, or so they say. I routinely get accuracy with wihtin 17 feet. That's way more accurate than needed for GPS navigation.

Spaghetti · 09-06-2004, 09:15 AM

The European space agency's Galileo satellite system was supposed to be pin-sharp accurate, but apparently the U.S. military had a moan about the signal conflicting with their communications (threat to national security or some bollocks) so they agreed the new system would only be about a metre out or so. Anyways, Galileo is supposed to be compatible with existing systems so good news for everyone, especially if it's true about the U.S. government downgrading the accuracy during wartime conflict, which these days seems to be all the time

wrwx617 · 09-06-2004, 10:13 AM

The main advantage to having a gyro aided navigation is their abililty to navigate through tunnels and underground where PC GPS will loose satellite and stop working. I will surely buy one if a company come out with a gyro aided GPS reciever for the PC provided that it is sold at a reasonable price($300 or less).

ptk · 09-06-2004, 02:06 PM

this has been discussed before.
all in all, if you navigate mostly around low build up area, conventional GPS is suffice for you.

however, if you navigate around high rise build up area (i am, i live in singapore), GPS signal drop out is a major issue.

Dead reckoning (GPS coupled with gyro + vehicle speed input) offers ideal solution. however, they don't come cheap.

alot of the OEM kit for high end cars use this system

commercially available kits are hard to come by.
here's a few company that offers it
1. Whitebream claims to be developing one
2. uBlox
3. Trimble
4. Point Research

kao

vision · 09-15-2004, 02:02 PM

Actual teme for ppl who driving alote in city with high buildings

BeamRider · 09-15-2004, 03:44 PM

The real issue is "why inertial navigation fails without GPS"

Inertial system are far less accurate and hard to use than GPS:
- you need to know your coordinates when the system starts
- you need to keep position while it initialise (some minutes in aircraft systems)
- you need to refix due to gyro drift (that's why they use GPS to correct position errors)

The good in INS is that they are a lot faster in response than GPS but we don't really need this kind of systems in our car.
What Pioneer and some others uses is a compass to correct the heading information from GPS when you're not moving or moving very slowly (an inertial system is far more complex!). When you loose GPS signal the navigator uses your last known speed and current heading to assume your current position.
This is absolutely feasable with our carputers: it's matter of finding a compass (similar to http://www.robot-electronics.co.uk/s...CMPS032004.htm) and write a small application to correct GPS messages.
Cheers

mykolJay · 09-15-2004, 04:04 PM

I never have an issue with being off the road.

Hardware - the Ebay GPS mouse (WAAS enabled)
Software - iGuidance v.20

antimatter · 09-15-2004, 04:38 PM

So even if i did buy one of these "commercial Gyro/GPS systems" could i use the current software (iGuidance2)? or would i have to use a special software that accepted the other data? I would assume that the software would have to support differential positioning before you could utilize it