Destination announcement off by 200 yards

[DrivingBlind]

I was driving back to work from a trip and didn't bother to turn my TT off when I got back to familiar territory.

When I was about 200 yards from my company (I used the exact street address), I got the "you have reached your destination announcement. If i had been unfamiliar with the area, the TT would have essentially directed me to the neighboring office buiilding.

Is this a known issue? Can I fix it directly on my device?

(I have the latest map)

Thanks!

DB

 

[dhn]

An example of incorrect mapping data. Without getting into details,, the fact is that precise street numbers are not stored as part of the map data.

For example, my gps 'thinks' my home is actually 8 houses away from me. So does Google, so does Mapquest.

It's bad mapping data.

 

[DrivingBlind]

OK thanks!

That's interesting. If addresses aren't stored how does a GPS determine where and when to make an announcement?

 

[canderson]

OK thanks!

That's interesting. If addresses aren't stored how does a GPS determine where and when to make an announcement?

Note that dhn said that "precise" addresses aren't stored. What is stored is a range of addresses along a particular length of street. Sometimes the range is a portion of a block, sometimes it is a great deal more than that. The mapping companies don't beat the streets identifying each and every addresses' location. So the GPS firmware tries to interpolate between sets of known start and stop addresses to determine where yours probably occurs on the street.

 

[JEfromCanada]

Approximating addresses

It is my understanding that map data contains information about the first address on a block (for example, the block might be the "2100's". The algorithm probably takes the length of the block, and given the user's entered address, calculates the offset from the beginning.

So, if the address is given as 2130, the GPS would assume you have reached your destination when you've gone 30% of the distance between the "2100" and "2200" block.

 

[JEfromCanada]

Canderson beat me to it!

 

[canderson]

Sometimes the data is even tighter than that. I've often seen a street broken into additional pieces smaller than a block (good for the user) simply due to the way the street bends. Not sure why that happens, but I take the additional accuracy freebies when I can get them.

The problem is that numbering is often not linear with distance (especially in commercial areas). Worse, the ending address is sometimes assumed (e.g., if the block starts at 2100, it may be assumed to end at 2199). That really skews things if the addresses actually end at 2151 or somesuch.

 

[JEfromCanada]

I used round numbers in my post, but I believe the algorithm is the same - based on the starting address for "segments" (as you indicated, there may be multiple segments based on curves in the road), and interpolation between segments.

Say I'm looking for 2130, and there is a segment beginning with 2100 and the next segment beginning with 2150.

My address is between those two numbers, so the calculated position would be 60% of the distance between the beginning of the first segment and the beginning of the second segment.

 

[DrivingBlind]

Thanks everyone. That explains it!

 

[canderson]

No jive.

Just had a buddy call from his car (no TomTom!) asking where the devil the Clay County library is in Middleburg, Florida. I tried to steer him there per the waymark created by Google maps. Boy - what a geolocation miss that was. You can see where Google thought its address was (Where the "A" is)... off a dirt road nearly to the end of a cul-de-sac. The library address is actually clear up in the upper right corner where you see the large building.

 

[Gr8marine]

Addresses are off.

I just got a Tom tom for Christmas, and mine is doing the same thing. I also have a Garmin in my other car and it is ALWAYS spot on the mark. I have NEVER had an issue with my Garmin giving me the incorect information. This is just an issue with Tomtom. I'm considering taking mine back.

 

[rustybirman99]

We chose the POI of the hotel we booked, and when Tom Tom said we had reached our destination, we looked and saw it on the other side of the highway with a divider in between. Luckily the hotel's name was high on the building so all we had to do was go to the upcoming u-turn to get to it. If you weigh all the attributes of Tom Tom and Garmin (and you want to be able to control how your GPS works as much as possible), you will choose a Tom Tom and put up with some of these minor problems. When I tested a Garmin, it took me off a highway exit and right back on at the next entrance for no reason at all. My TT has never done that !!! Garmin is simple for those who do not want to be involved in extra option settings. They will both get you to your destination eventually. Our Tom Tom got us close enough that we found the hotel easily enough AND automatically routed us around a major traffic jam which made our friends arrive an hour later than we did !!

 

[Rick F.]

I just got a Tom tom for Christmas, and mine is doing the same thing. I also have a Garmin in my other car and it is ALWAYS spot on the mark. I have NEVER had an issue with my Garmin giving me the incorect information. This is just an issue with Tomtom. I'm considering taking mine back.

Some folks like TomTom, others like Garmin. To each his/her own. I guess it's like PC vs Mac. Each has their fans.

Good luck in your decision.

 

[thetalk]

I always go to googlemaps or google earth and find the exact coordinates for a location whenever possible. We went to a concert last month and found a parking lot nearby the arena (which we never would have found via the street address). With the overhead shots available these days you can practially put in coordinates for the exact parking space!