Garmin Mobile PC vs Garmin Nuvi 7XX accuracy

I currently have a Garmin 755T and I am very happy with it. However, I would like to use a netbook and Garmin Mobile PC, but so far, I am a bit dissatisfied with the accuracy I am getting on Mobile PC vs the accuracy of the Nuvi. With the Nuvi, the tracking is smooth, and as I see street signs at 30 - 40 MPH, the Nuvi shows accurately that I am approaching and passing each street. Mobile PC is not as accurate as I can pass a street and it takes a few seconds for Mobile PC to show that the street has been passed. Also, the Nuvi tracks my speed near perfect, but Mobile PC, lags a few seconds behind. When I stop, the Nuvi speedometer goes to zero quickly. Mobile PC on the other hand rarely makes it to zero before I am moving again. I am currently using an Ambicom BT-GPS, which has a Sirf III chipset. After researching, it seems that I need a 5HZ GPS, like the I.trek M7 for more fluid movement, but I wonder if someone could tell me if it will track more like the Nuvi does or if you just can't get that kind of tracking on a PC/GPS unit. If I was traveling and had not made a predetermined route, but I was looking for a certain street, and lets just say that there were no street signs available to me, I would probably be ok with the NUVI as the tracking for street ahead is almost perfect. I would be in trouble with Mobile PC as I would already pass the street before Mobile PC would show that I actually passed it. So, I am looking for a solution with Garmin Mobile PC that would be near equivalent to the Nuvi. Will a 5HZ GPS accomplish this? I am not really open to other mapping programs as I like Garmins routing the best, but I would like to go with the netbook as a mobile wifi and Garmin mapping solution. Thanks!

You didn't say what computer you are using to do the testing with? How fast is the CPU and how much RAM?

I've heard these problems described with at least a couple of other programs but this is the first time I've heard it with Mobile PC.

...ken...

It is unlikely an issue caused by Garmin Mobile PC software, or an issue of your SiRFstarIII GPS receiver.

5Hz is nice to have, and it does indeed make the map movement more fluid, but even with 1Hz unit your Garmin Mobile PC should work just fine.

I have used Garmin Mobile PC a lot on an ASUS UMPC with a crummy Celeron 900 chip 1.2G memory and multiple things running in the background to support the device. I had problems but map updating was not one of them. It is easily the match for my Nuvi 750 in this respect.

Could it be due to where you are placing your GPS receiver? GMPC will show the satellites being used if you click on the satellite symbol in the top right hand corner of the screen and choose 'GPS Info'. BTW your 755 will do the same thing if you touch the icon in the top left for about 3 seconds.

Terry

Okay, the original post prompted me to go out and spend a big chunk of the afternoon with my laptop and a variety of GPS receivers in the car. My arsenal included the following:

Mobile PC v5.00.50
iNav iGuidance2009
Mappoint 2009

Pharos 500 USB
Globalsat BU-353 USB
i.Trek M7 Bluetooth
Garmin GPS10x Bluetooth
Garmin eTrex Legend HCx handheld connected by USB

(I could not persuade my Navation 168 USB to work, no way. Tried three different cables and couldn't get data from it.)

I don't have a Nuvi so to do a similar visual comparison as the original poster and get my own reactions to the visual differences I used my Garmin iQue 3600A which is very smooth to view and very positive on speed changes.

In a nutshell, all three PC nav programs do what the original poster described.

The apparent jerkiness of the moving map is a function of the difference in screen size. On the small screen of a handheld or other personal navigation device the map doesn't move very far even when you are travelling at high speeds, because the screen is so small. However, on the large laptop screen the movement is very apparent and looks quite jumpy by comparison. The faster you go the jumpier it looks because when the screen updates with the new position each second, you have moved a fair piece down the road.

To do a fair comparison with the handheld you would need to hold it about six inches in front of your nose, and then you would see the same relative jump with each position change.

Regarding the speed display keeping up, part of that is simply the lack of synchronization between the handheld and the laptop. That is, the receivers will be sending new position information as much as nearly a second apart. It also takes your eyes a good portion of a second to track from one screen to the other.

I can see what the original poster was talking about because with most of the receivers I tested I saw the same lag when speeding up and slowing down, with the laptop not showing the speed increases or decreases as fast as my iQue.

Here's the thing, it did it with Mobile PC, Mappoint and iGuidance. All lagged my handheld a small but noticable amount.

I did discover two very interesting things. Both demonstrated that it's all in the receivers.

First, with my eTrex Legend connected, I was able to set the eTrex close enough to the laptop that I could take in both displays in a single glance. The speeds tracked nearly perfectly between them. With both of them displaying speeds to the tenth of a kilometer (xx.x kph), there was never a variation of significance. That means the positional information was being received, processed and displayed by Mobile PC on the laptop pretty much as fast as it was being processed and displayed in the eTrex. In both cases there was still a small apparent lag behind my iQue 3600A both increasing and decreasing speed.

Second, with my Garmin GPS10x Bluetooth receiver connected, there was no apparent lag between the speed displayed by Mobile PC, iGuidance or Mappoint versus my iQue 3600A when increasing and decreasing speed.

To put it into perspective, my iQue 3600A also has some lag in the speed display. When I have stopped completely, it takes between one and two seconds for the display to settle to Zero. And it takes one to two seconds of movement for the speed to start climbing when I start up again. This is to be expected when you understand how a navigation program or personal navigation device works.

In contrast, the laptop programs all had an apparent lag of perhaps one additional second when connected to everything except the GPS10x receiver.

Part of that apparent differential could be overcome by killing the tenth display. iGuidance displays in full MPH or KPH (no tenths displayed). This has the side effect of making it appear both more responsive and more stable.

Bottom line is that if you want the same sort of apparent responsiveness of the Nuvi, it's all in the receiver so spend the bucks on a Garmin GPS10x Bluetooth receiver to use with Mobile PC. It's big bucks.

And it really does not buy you anything in navigational usability.

That's really the bottom line. All of the receivers worked well. None had anything over any of the others to justify any significant price differences.

All of the navigation programs have the same display jump when they update the screen for the new location every second and all look jumpy if you compare them side-by-side with the display of a small personal nav device.

The only thing I didn't test was cranking up the refresh rate on the i.Trek M7 to 5 Hz. I don't have the necessary software installed on my laptop. I am sure that it would have supported Marvin's and Terry's experience that it smooths out the display because you can't move far enough in a fifth of a second at any sane and rational speed to cause big jumps on the screen.

Truly, the simplest and cheapest solution to the original poster's problem is:

Option A: turn off the Nuvi when you're using the laptop, or
Option B: use the Nuvi and forget the laptop for nav.

If you only use one or the other you won't notice those little differences.

Two more things I want to mention.

I really love Mobile PC's ability to discover any type of GPS .. Bluetooth, true USB, and even very high numbered fake COM ports from a USB-Serial driver. To get iGuidance and Mappoint to work I had to use GPSGate. That way they always saw a COM port and it was always a nice low number.

iGuidance has the nicest navigation display of the three. By a wee bit over Mobile PC and ... well, Mappoint/Streets&Trips just sucks in that department, especially if you don't have a route active. In my judgement.

...ken...

Very interesting tests Ken and I can see how a larger screen would cause larger jumps between samples. However, this should not affect how soon GMPC identifies the next street as this is not a function of how far apart they are on the display. If that were the case, increasing the scale would make it work better as the streets would appear further apart.

Lately, I have had to use the speedometer as mine is being flakey. I note that both the Nuvi and GMPC update at about the same rate. I am not concerned with when they go to zero as I can usually tell when I stop.The disadvantage of the Nuvi is it doesn't show the speed in navigation mode; GMPC does.

I agree that in landscape mode, iNav presents a slightly better picture of the map as it wastes less space on menus and borders. In portrait mode this is not an issue. Now if iNav was just a little more usable and had the same amount of POIs for my area, I might give it more time.

Terry

The issue is not with the netbook (a Dell Mini 9, with 1 GB of memory) as I have also tested it with a 2.2 GHZ core 2 duo notebook with 3 GB of memory. The placement of the bluetooth GPS receiver was actually more closer to the front of the car than the Nuvi (it was sitting on the dash as close as the windshield would allow and had a better "view" of the sky). The Nuvi was on a windshield mount about a foot behind the bluetooth unit, but nevertheless, I do not believe that the signal is the issue here as both units were receiving very similar signals.

My issue is not because the screen is larger and just shows the 1 second updates clearer. I feel fairly confident that the NUVI is not only given the GPS data on a more frequent update than one second, but also that is uses its proprietary software to do the things that it does so well. Although I don't recall testing this, I feel confident that if I pull up to a road at 25 MPH and stop, the car icon on Mobile PC will not stop as soon as I stop, but actually catch up to the accurate placement of where I am and then stop. The Nuvi does this immediately when I stop so the placement is just about perfect as soon as I stop. The speedometer (which the NUVI 755T has on the main map screen) is far more accurate than the one on Mobile PC's main map screen because again, it does not seem to play catch up like Mobile PC does.

If you were testing these units on the interstate at a constant speed, both the NUVI and Mobile PC would track speed fine. However, if you increases speed 2 MPH for a second or two and then back down 2 MPH, the NUVI would change almost identically to the car speedometer. Mobile PC would lag and would not update the changes until a few seconds after they occured. I have tried a different USB/GPS unit with Mobile PC and it's just as bad. Even so, I feel that the issue is with the receiver as I have yet to try the Garmin receiver or a 5HZ receiver. I would be very curious if someone could test with a Nuvi 7XX series unit against Mobile PC and a Garmin GPS10X and see if they react the same as Ken in Regina implied but was not able to test against a Nuvi.

I would also be curious if the Garmin GPS10X is a 5HZ receiver or what are the exact modifications to that particular unit that would make it work so much better with Mobile PC? Maybe because of a Garmin specific protocol vs NMEA?

Please do not misunderstand me and think that I am trashing Mobile PC. Mobile Pc would okay for predetermined routes as the warnings are enough for you to understand when to turn, etc. However, I do not like the fact that the data from the GPS lags on the screen, unlike the NUVI 755T. I would prefer to use GMPC over the Nuvi, but I would also like GMPC to update on the screen so that when I pass Main ST in my car, GMPC shows that I just passed Main ST. The way it is now, I can pass Main St in my car and it takes GMPC a good 3-5 seconds to show that I have passed Main St. Maybe this is the norm for most units, but the Nuvi does not do this. When you pass Main St, the Nuvi shows that you are passing Main St. Thanks for your time.

P.S. I don't know why my paragraphs are all running together after I posted this, but they keep getting joined together when I save changes.....sorry

edit: I am trying to add the paragraphs again, this time with javascript on and using the "Go Advance" button, "Preview Post", then posting.....it worked on my post below.....so we shall see.

All my previous on-road usage of GMPC was with a Garmin 10x. I didn't realize that would make a difference until Ken mentioned it and will try some real world testing with some of the other units I have.

Yes, it was very difficult to read your post with no paragraph breaks.

Terry

I'll bet you're cutting and pasting into the forum from a word processor on your PC. The carriage control characters (CR, LF -- equivalent of the Enter key) are not translating, or aren't even in the source text. If that's the case, try a different editor (perhaps a true text editor like Notepad) or use the forum's online editor. Or compose offline, cut/paste, do a preview and fix the paragraph breaks with the online editor.

My previous post was rather long so I'll repeat that the lags I noticed in speed changes and vehicle icon location on the map relative to intersections were not specific to Mobile PC. They were consistent to all three nav programs that I used. That's why I said I'm confident it's a function of the receivers.

The slight lag in position of the vehicle icon relative to intersecting streets that I noticed in my testing was as minor as the speedometer display lag. It was insignificant to any safe kind of navigational use.

With my iQue 3600, when my car is fully in the intersection, the cross street almost exactly intersects the centre of the vehicle icon. With all of the PC nav programs, with all of the receivers, the nose of the vehicle icon was generally just touching the intersection as I was fully in the intersection. The lag was never more than a vehicle length.

The Garmin GPS10x performed precisely the same on all three PC nav programs so Garmin clearly has not done any tweaking specific to using it with Mobile PC.

Finally, an observation....

The only time the visual lag on the laptop screen will affect your ability to navigate is if you are trying to use it for visual navigation rather than audio guided navigation.

In my opinion, that's simply not something you should be attempting to do with either your Nuvi mounted in line of sight and you surely shouldn't be trying to do it with a laptop that cannot even be placed in line of sight in most cases.

And if you insist on trying to use these devices for visual navigation, a lag of a carlength, or even a couple, isn't an issue. In the first place, it's consistent so you know exactly how much to you need to "lead". In the second, the faster you go, the bigger buffer it gives you to make an upcoming turn.

...ken...

I know my memory is failing and I used the Nuvi just yesterday but isn't the following true. In non-navigation mode, both Nuvi and GMPC (and iQue/ XT) show the upcoming street in a banner above the screen. I assume that is what we are discussing.

Terry

I am not coping and pasting. I am typing everything in the quick reply section below. I do have javascript on now, so maybe that will help - we shall see.

No, I am not testing the "upcoming street" notification in non-navigation mode, which I think Garmin was no longer allowed to use on the Nuvi I have due to copyright problems (if memory serves correctly). I am testing a problem with Garmin Mobile PC in that it seems to lag in both speedometer readings as well as the map display. Once you are moving at a constant rate of speed, I do not notice the speedometer reading accuracy problem so much, but I still notice that GMPC does not (with my hardware and test) track oncoming intersecting roads accuratly. It takes a few seconds for the GMPC map display to show that I am passing a intersecting road, when in fact my car has already passed it. The Nuvi 755T (and 750 that I've tried) do not exhibit this issue so blatantly.

Ken in Regina - either you and I are testing differently, or misunderstanding each other in how we are testing, or our results are simply much different. My results with GMPC do not leave the car icon touching an intersecting road when I pass it in my car. I have not tried stopping at the intersecting road to see if it "catches" up (which I think it will) because that was not my issue, but when passing intersecting roads, GMPC is a few seconds behind the Nuvi in updating the car icon on the map screen.
Since you do not have a Nuvi to test with, I can conclude that you are not aware of the differences (if there actually are or are not) between the tracking performance of GMPC and the Nuvi 755T. You certainly have a right to your opinion about what I should or shouldn't do and what I should or should not expect with my GPS system. Even so, I am still interested in the answer to my question from others who may be able to provide it. I don't think you will be able to help me answer it since you do not have a Nuvi 7XX to compare. If you can get access to a Nuvi 7XX that you can compare with, I would be greatful for the test results.

Thanks to all for your time and help. Again, I am just wondering what differences in tracking that there might be between GMPC and the NUVI 7XX series and what it would take to make GMPC perform like the NUVI 7XX series. I can certainly keep the NUVI and use it for my particular application, but I would prefer GMPC.

After reading through the post again, I just noticed that my Mobile PC version is 5.00.60 and Ken in Regina's is 5.00.50 - I wonder if that could be the difference between our test results?

If I am completely misunderstanding your problem, please forgive me, please ignore the following and try to help me understand what the problem really is.

When I drive through an intersection, my iQue 3600A shows the vehicle icon smack in the centre of the intersection exactly as my vehicle is smack in the centre of the intersection.

Said another way, as I drive through an intersection, the line of the intersecting street/road almost exactly bisects the centre of the vehicle icon on the display as the actual intersecting street/road is off my left and right shoulders.

No stops involved here. Just observing as I drive through an intersection to try and determine any lag in the display of the vehicle position. There is no apparent lag in the vehicle icon display on my iQue 3600.

Can you describe, with a similar example, how your Nuvi is more accurate than that, in terms of where the vehicle icon is displayed on the map versus where your vehicle really is, please?

When I use this same observation with the PC nav programs as I drive through an intersection, I see that all have a lag in the display. The front tip of the vehicle icon appears to be just entering the intersection, or just slightly before entering, at the point where my car is passing through the centre of the intersection.

I use that description because the only place I can tell, visually, how much the vehicle icon display lags my actual vehicle position is at intersections. Using this method of observation it appears that the vehicle icon in the PC nav programs lags my real position on the road by roughly a vehicle length.

These observations were done at city street speeds, typically 50kph speed zones. Faster speeds would, of course, show a larger visual lag of the vehicle icon.

Are you seeing a bigger lag than that with Mobile PC? You have not given us an example that allows us to quantify just how big a lag you see with it. I have tried to do that as best I can. I would be interested in a comparison using the same metric I did above ... as you drive through an intersection, where is the vehicle icon being displayed on your Nuvi and on your laptop versus where your vehicle really is.

As far as the lag in the speedo display, there is a guarantee of 1 second in any device that has a GPS reading refresh rate of once per second (1 Hz). I'm seeing almost exactly that amount of lag on my iQue 3600A. If you are seeing less than a 1 second lag on your Nuvi, that can only mean that it's refreshing the readings more frequently.

I have no idea why some of the receivers I tested -- all except the GPS10x -- produce a little bit longer lag on the speedo display. For some reason there seems to be about an additional second lag. It's close enough that it's surely no more than that. Trying to guage it visually is difficult and the difference is small for any sort of manual measurement, like a stopwatch.

I went into this testing thinking that the explanation of any lag would be the latency (delays) of having the GPS receiver external to the device ... having to wait for the position data to go through the cable and the driver software before the PC nav programs even see it. I was persuaded otherwise by the results from my eTrex Legend (virtually identical speeds on the built in display of the eTrex and the PC nav programs, suggesting no significant lag due to the connection length) and the GPS10x (no lag versus my iQue).

As I said at the start, if I'm completely misunderstanding the problem please forgive me. If it's simply a difference in the amount of the lag you are seeing versus the amount of lag I'm seeing, perhaps some specific examples that would help us understand the magnitude of the lag would allow us to help with some testing and perhaps troubleshooting if that seems warranted.

...ken...

I doubt it. None of the listed changes to .60g are related.

It would be helpful if you could give us an idea of what your test results are with some sort of examples similar to what I've described so we can visualize what's happening and compare. For instance, when you drive through an intersection at city street speeds, where is the vehicle icon being displayed relative to where your car really is as it pass through the dead centre of the intersection?

If it sounds like our test results are significantly different I'll be happy to update my laptop to Mobile PC 5.00.60 and retest with a couple of receivers.

...ken...