TT1 GPS Accuracy (newbie question)

[gps.chick]

My TT! announces "you have reached your destination" about 3 houses away from my home address. I also notice the same thing when navigating to any destination. It's like it's off by 75 meters. Anybody else have this problem? Is there a setting I need to correct somehow, e.g. compass or something?
Thanks.

 

[dhn]

My TT! announces "you have reached your destination" about 3 houses away from my home address. I also notice the same thing when navigating to any destination. It's like it's off by 75 meters. Anybody else have this problem? Is there a setting I need to correct somehow, e.g. compass or something?
Thanks.

No, that's quite normal (to be off by a few houses). Mine shows 'home' 8 houses away. It's a reflection on the maps being used, not the GPS.

Some roads......it gets the destination exactly; others, as you've observed, it can be off somewhat.

Further, if you have TTS text to speech), you will hear the 'reached your destination' before the tomtom shows you actually getting to the checkerboard (destination) icon.

 

[gps.chick]

No, that's quite normal (to be off by a few houses). Mine shows 'home' 8 houses away. It's a reflection on the maps being used, not the GPS.

Some roads......it gets the destination exactly; others, as you've observed, it can be off somewhat.

Further, if you have TTS text to speech), you will hear the 'reached your destination' before the tomtom shows you actually getting to the checkerboard (destination) icon.

Thanks dhn. Are there better maps available so this doesn't happen? btw I live in Guelph - not too far from you

 

[Rick F.]

I've noticed the same thing when I first started using my TT 3rd edition.
...see this thread:

Home Postion wrong:
https://www.tomtomforums.com/showthread.php?t=5438&

Sometimes it's very accurate -- but not always.

 

[dhn]

Thanks dhn. Are there better maps available so this doesn't happen? btw I live in Guelph - not too far from you

Nope. I have the latest (NA 7.10 build 1609) and the displacement exists.

 

[bootprint]

It's prefectly normal for that to happen, the maps for Garmin and Tomtom both can have this issue.

Its the way they generate the addresses, mostly likely to save map space.

Say a road is 1000 metres and the first address is 1 and it finishes with 201. They divided up the road up by 5 metre increments to get the addresses. But the problem comes in if each property isn't 5 metres wide or has a park or something.

You could reset Home to the actual driveway. While in the driveway press 'Change preferences', >, >, 'Change Home location', >, 'My location'

 

[danzeb]

My TT! announces "you have reached your destination" about 3 houses away from my home address. I also notice the same thing when navigating to any destination. It's like it's off by 75 meters. Anybody else have this problem? Is there a setting I need to correct somehow, e.g. compass or something?
Thanks.

A GPS knows latitude and longitude. When you give it an address it has to guess where your house is based on the house number. The map will know what addresses are on a street but won't know there exact location. When all the address on a street are evenly spaced and the numbers are in proper sequence it can do a pretty good job.

I don't think a database exists that has every house number matched to their latitude and longitude.

 

[Kegan36604]

I'm a lay person at best on this stuff, but here is an observation I have made. If I search and identify an address from my PC, save it as a favorite, and then load it to my TomTom, I will discover what you mention-> the location may be off a litte. If I go to a location, stop and then enter it into favorites directly into the TomTom, it is and stays accurate.

I have noticed some odd road placements on the GPS that quite frankly I suspect is the source of the map data (i.e. the county GIS system or where ever they are getting road info from). In other words, the TomTom knows where it is. The satelittes know where they are. The county isn't quite sure where it's road is!

 

[dhn]

I'm a lay person at best on this stuff, but here is an observation I have made. If I search and identify an address from my PC, save it as a favorite, and then load it to my TomTom, I will discover what you mention-> the location may be off a litte. If I go to a location, stop and then enter it into favorites directly into the TomTom, it is and stays accurate.

Because when travelling, the satellites lock into that position when you save it as a favourite.

But, the map really doesn't know the precise location (satellite speaking) of 123 Main Street, Anytown so the location it provides you may be off somewhat .... and usually is.

 

[ludde28]

TT is forcing the cursor to "a street possition" if you are say 10-20m off road.
Try turn on your TT in your backyard, staying 10-20m from road, and cursor will appear in the street.
This is because TT is made as a "carnavigator", witch means that you are suppose (TT thinks) to drive "on roads not off".
This is also made to avoid GPS-signaldistorsion, witch can be upp to 5-20m.

 

[gps.chick]

:

It's prefectly normal for that to happen, the maps for Garmin and Tomtom both can have this issue.

Its the way they generate the addresses, mostly likely to save map space.

Say a road is 1000 metres and the first address is 1 and it finishes with 201. They divided up the road up by 5 metre increments to get the addresses. But the problem comes in if each property isn't 5 metres wide or has a park or something.

You could reset Home to the actual driveway. While in the driveway press 'Change preferences', >, >, 'Change Home location', >, 'My location'

Excellent idea! Thanks.

 

[dhn]

:

Excellent idea! Thanks.

You may find that the location it places you is accurate but it will not match the location it thinks is your street address number. No big thing.

 

[Alon]

TT1 S30 - accuracy issue

My new TT1 S30 is off by 15-25 meters not just on house number but also on intersections, when I'm ON or IN the intersection of streets it show as thou I have 15-25 meters to go...... When I make the turn, it adjust itself and keep guiding me further.
So, in the CBD I keep missing the turns as TT shows I got say 75 meters to turn...50 meters......25meters.....I missed the turn AGAIN!!!!
Does anyone have a similar issue?

 

[dhn]

You could try to get a recent gpsquickfix and see whether that helps. Also, the map version (what version do you have?) may need updating.

Having said that, if you have the next street displayed on screen, that plus the visual and audio warnings that you are getting close PLUS the direction arrow you need to turn should all result in your not missing a street you need.

If you take the verbal cues absolutely literally and not turn until the precise distance the unit says to, I'm afraid you may wind up in a news article similar to those about people blindly following their gps with the result that they wind up going into rivers, railroad tracks, etc.

Use common sense with this or any gps unit, that's all I'm saying ..

 

[1XL-on-XR650L]

One thing I have noticed is that the verbal warnings occur differently in different navigation modes (car v. pedestrian). The warnings happen less often, and closer to the event (turn, destination, whatever) when in pedestrian mode. I only know this because I sometimes set my TT to pedestrian mode while navigating local neighborhood areas on my motorcycle, and there are a bunch of “foot bridges” in my area that the TT recognizes as walking paths, but not roads (my dual sport motorcycle is not fussy about hopping curbs or negotiating a few stairs). One day I forgot to switch the mode back to “car” after being in pedestrian mode, and noticed a completely different set of warnings for a route that I travel frequently in the car. I suppose it makes sense not to warn a pedestrian about a turn ? mile ahead, after all just how much warning do you need moving at less than 3 MPH? That would be something like a 10 minute warning, right? Haah!
Side note:
My Tomtom (ONE XL) is geographically correct to within about 20 feet. I know this because I use it to play a game called “geocaching”. In that game you use your GPS to find stuff that others have hidden and then posted the longitude/latitude coordinates on the internet. I do have a dedicated hand held GPS for this task (Garmin Vista HCX), which is touted as being one of the more accurate in its class (short of a professional surveyors $2,500 equipment). The Tomtom gets me just as close to a predetermined set of coordinates as it does 95% of the time! Any positional error you are seeing is most likely caused by map errors or software shortcuts in voice commands.

 

[mjacobs9]

My TT! announces "you have reached your destination" about 3 houses away from my home address. I also notice the same thing when navigating to any destination. It's like it's off by 75 meters. Anybody else have this problem? Is there a setting I need to correct somehow, e.g. compass or something?
Thanks.

The error is most likely not maps but the lack of correction data supplied by the land based WAAS system. Satellite GPS data contains errors because of satellite location drift, atmosphere interference, etc. If a GPS unit is WAAS enabled, typically not a service fee but just a feature of the GPS unit, the satellite data is corrected by the land based WAAS signal system.

Accuracy from satellite could vary by as much as a 100 meters. Satellite with WAAS is less than 3 meters. The eight house error cited would approach the 100 meter error meaning the unit is most likely not WAAS enabled, or signal reception from satellites is not good. The satellites are fixed (as best as technically possible) over the equator. A clear line of sight to the horizon is needed for GPS units to be right on. And, the WAAS correction increases the accuracy.

 

[sageuvagony]

Nope. I have the latest (NA 7.10 build 1609) and the displacement exists.

I was VERY confused when I read this and was thinking dhn was losing his mind, but then finally noticed the date on his post.


Wonder what goes through people's minds as they are reviving old threads

 

[dhn]

Sage....you're convinced I've lost my mind anyway, haven't you?