G35

I don't know if it's the i-Blue receiver or the iG 2.1.3 software, but the position of the car on the screen lags from my actual position. This can be a little tricky in crowded areas because I overshoot a turn. Do other people have this issue? Is there any way to improve the accuracy or decrease the lag? Thanks in advance.

JakeRich

All GPS systems lag by about a second. See the two tutorials in my sig for the technical reasons. Can't do anything about it, it's the way the system works.

tap0utt

imo, tomtom does not lag as much as iguidance. the timing is almost about right, and the car mov't is smoother. not jumpy.

jaimelobo

Originally Posted by tap0utt

imo, tomtom does not lag as much as iguidance. the timing is almost about right, and the car mov't is smoother. not jumpy.

Have to agree with you, iGuidance does seem to have more lag than others do. Before I got my Axim, I was first using MS S&T on a laptop and I was surprised by the accuracy. There were many times when my wife was driving, I would watch the laptop to check the accuracy, and the indicator would be dead on as we passed under an overpass on the highway at 75mph.

Before I got iG3, I borrowed a friend's Axim with the Dell version of iG and noticed the lag, I assumed it was just due to the CPU of the laptop vs the Axim; but then I loaded S&T pocket maps (or whatever it's called), and it was more accurate at locating a position.

Even though the "lag" would be inherent in the system, it seems that some of the other programs are using a better algorithm to introduce a "lead" to offset the delay.

JakeRich

Originally Posted by tap0utt

imo, tomtom does not lag as much as iguidance. the timing is almost about right, and the car mov't is smoother. not jumpy.

The smoothness is artificial. They get one fix per second, no more. That's the way the GPS system is designed. What TT does is to estimate where you "SHOULD" be between fixes, not where you actually are. That forecasting sort-of works most of the time, but if you are changing velocity or direction, the forecast is wrong. Also, lag/lead on maps depends on map data. See GPS201 for an explanantion in some detail. Aggressive snap-to-road, like TT uses, exacerbates any error in plotting the position on the road.

tap0utt

my reply might have been a bit confusing.

let me rephrase to show clarity. my term for:

lag=spot on map at instantaneous spot in real life.
smoothness=motion of screen car movement.

but yeah, when i tested out iGv3 while driving the results came back that when i passed up a street, iGv3 showed that i havent passed up the street yet. maybe a few more yards. that bothered me. i know that i can be a bit picky, but this annoyed me. I liked the real time point of TT better. it may be different according to different maps, I was using both in the state of FL.

IDK, so my point was that i believed it to be the iG software as opposed to his i-Blue GPS system.

rcab

I have Iguidance and I notice a little lag with my globalsat bt-338 on x51v, but most of the time it pings just as I come up on a street to turn. So far the lag has not caused me to miss a turn.

tap0utt

Originally Posted by rcab

I have Iguidance and I notice a little lag with my globalsat bt-338 on x51v, but most of the time it pings just as I come up on a street to turn. So far the lag has not caused me to miss a turn.

yeah, it has never caused me to miss a turn either, i am just a little picky. that is all :hide:

JakeRich

Originally Posted by tap0utt

my reply might have been a bit confusing. let me rephrase to show clarity. my term for: lag=spot on map at instantaneous spot in real life. smoothness=motion of screen car movement. but yeah, when i tested out iGv3 while driving the results came back that when i passed up a street, iGv3 showed that i havent passed up the street yet. maybe a few more yards. that bothered me. i know that i can be a bit picky, but this annoyed me. I liked the real time point of TT better. it may be different according to different maps, I was using both in the state of FL. IDK, so my point was that i believed it to be the iG software as opposed to his i-Blue GPS system.

Exactly my point. None of the systems can actually show where you are if you are moving because all of them show where you were about a second ago. That is the physics of the system. What TT does is to anticipate what it thinks you are going to do and changes the display accordingly. But if you don't do what it expects, it forecasts improperly. This problem manifests in a couple of situations: If TT has directed you to turn at a stop sign, and you don't make the turn but go straight, when TT sees movement, it assumes you are turning and turns the display. It catches up eventually (1-2 seconds) but it's still predicting incorrectly. The same thing happens if you turn when it isn't expecting you to do so. It predicts you'll continue straight on the commanded path and shows that instead of your turn.

iG, on the other hand, doesn't predict, it just displays where you were about a second ago. At 25 MPH, that lag is about 36 feet, or 12 yards. That lag is about the same as the error radius of the fix itself, by the way. Add to that distance the errors that most maps have (see GPS201 for a specific example) and most of the time the intersections will be slightly off. The ones that you would see "early" are masked by the GPS lag. The ones that you'd see late even with no lag have exaggerated lag, making it look worse than it is.

Most routing software gives you warnings of upcoming turns so that you don't get surprised.

tap0utt

ah, that's a very good explanation jakerich.

thumbs up to you.

sz1999

Even my garmin lastest handheld 76Csx has a lag, in the dense city, i missed some turns due to the lag(i don't have routing software giving warning). But once I know this fact, it is not big deal. The point is the faster your speed is, the bigger the lag is.