off by 100 metres or so for addresses

[Andy_P]

I think that getting an EXACT position for every address in the world would be a fairly impossible task, so it's obvious some sort of 'guesstimation' has to be used.

If you have a road with 100 houses evenly spaced along it and the TT knows that #1 is at one end and #100 is at the other, it willl probably have a fairly good guess.

But in a rural area where you may have small clusters of cottages in several spots along a long, winding road, it's sure to end up being only approximate.

 

[Arno]

I think that getting an EXACT position for every address in the world would be a fairly impossible task,

Andy,
I think it more a question of money.

When we built the Live Steam track a Roundhouse Park in Toronto a few years ago, the General Contracter, working for the city, had a unit, about 8 inch square and on a 5 foot pole, that had a 20 mm accuracy. The unit did cost several thousand dollar and had an annual subscription fee of over $ 1,000.
For surveying purposes GPS with a resolution of 2 mm are available now.

I am wondering how current inaccuracies to house numbers are introduced.

You will remember that I wrote about accurate Mapquest and Navteq maps at about April 2008 all of a sudden shifted my street address 80 m to the west and onto the south side of the street.
That was still the case when Google used Tele Atlas but since they now use their own maps in North America the error is only about 30 m.

I still cannot figure why they were correct and then changed.

(Still got my eMail correspondence with Navteq as I had almost decided to purchase a Magellan GPS.)

 

[Arno]

This error was noted using my TomTom today.
I made a report to TomTom and instead of just passing on my lousy cell phone picture decided to give the location for a Google street view.
Putting in the route Google showed the same error as TomTom so I made an error report to them (click RH bottom of map, next to the arrow).

Here is the acknowledgement from Google:

Hi Arno,

Thanks for taking the time to report a problem with Google Maps:

"Because the street addess has the usual 20 - 30 m off set to the west the
map will not allow the left turn on WB Kingston Rd. into the drive way of
Tim Hortons. The marker shows the actual building. At the destination B
location the centre safety island is in effect and a turn cannot be made
there, thus the U-turn at the Sheppard/Port Union light. Google street
view, if dragged to the actual building shows the interrupted safety island
and drive way very well. "

We'll send you an update once your report has been reviewed to let you
know the resolution.
Thanks for helping us to improve Google Maps!

 

[Andy_P]

the General Contracter, working for the city, had a unit, about 8 inch square and on a 5 foot pole, that had a 20 mm accuracy. The unit did cost several thousand dollar and had an annual subscription fee of over $ 1,000.
For surveying purposes GPS with a resolution of 2 mm are available now.

Hang on... isn't that something totally different?....

Aren't you talking there about a GPS system with great POSITIONAL accuracy? (i.e. telling you where the box itself is, very precisely)

I maintain there's no way ANY unit can have every address in the world listed against it's exact Lat/Long coordinates. It's all educated guesswork, just knowing how many addresses there are along a certain stretch of road.

 

[Arno]

Aren't you talking there about a GPS system with great POSITIONAL accuracy? (i.e. telling you where the box itself is, very precisely)

I maintain there's no way ANY unit can have every address in the world listed against it's exact Lat/Long coordinates. It's all educated guesswork, just knowing how many addresses there are along a certain stretch of road.

The cartographers get the street address locations from the municipalities.
I cannot see any reason why in my street, where the lots are approx. 15 m wide the GPS location would return the large off set we are seeing.

Since a couple of months, when I hack in my address at Google it shows the map at 2/3 of the screen but on the left it shows an exact picture of my house, ready to turn into the drive way.
When I put the little man on the A location balloon pointer my drive way and garage are tight in focus.
But now comes the crazy part, when I right click and click on "What's here?" it puts the green pointer on my correct location but the A balloon 350 m down the street and shows the correct address for that location.
Additionally, when I click "Get directions" it has the coordinates in the B address field and when I enter my street address in the A field it calculates the distance as 1 m and shows that driving time is 0 secs but that I could walk to there in 1 sec.

 

[Andy_P]

Since a couple of months, when I hack in my address at Google it shows the map at 2/3 of the screen but on the left it shows an exact picture of my house, ready to turn into the drive way.

That's an on-line system with Google's humongous server power behind it. Your TomTom has a few negs of RAM and a couple of gigs of storage for the map. There's simply no room for the amounts of data required.
I

But now comes the crazy part, when I right click and click on "What's here?" it puts the green pointer on my correct location but the A balloon 350 m down the street and shows the correct address for that location..

I think that's all down to Google trying to be helpful (a.k.a. pandering to their advertisers). If you enter a set of Lat/Long coordinates, you get a green arrow that should be in the right place, but you also get a pink "A" which is where they "thought" you might have meant. In their help files they say

If searching for a lat/long you may get a green arrow pointing exactly to the lat/long and a red marker showing the "reverse geocoded" and named location.

Usually the red and the green markers are on different places on the map and strangely enough, that's often the location of someone who advertises with them!

 

[fred9]

I have a xxl540 and a 2405 and on both I find that at turning intersections the GPS seems 100 yards "ahead". That is I need to turn before the device/map seems to indicate the turn??

 

[dhn]

Quick question ......... do you have many (more than, say, four) categories of pois set to show on your map? Having lots does cause a retardation of screen refreshing............

 

[fred9]

Not sure I understand the question but
1. I haven't added any POI's to either device
2. I usually don't have any poi's showing on my map.

Thanks

 

[dhn]

Well, there goes that theory.......

Is the 'slow turn' happening every time or do you get a sense it may be when the gps signal is not the strongest (such as in cities with high buildings on the area)?

 

[fred9]

I was out today using my gps and now I think it's fine. That is when I'm at or passing an intersection the "car" on the gps map is only a few yards behind where I'm at.

So I'll now withdraw issue.
But thank you for responding.

 

[canderson]

I have the opposite issue with my GO1535. Unlike any other TomTom I've played with, this one always seems to show the blue arrow just a bit ahead of where I am! When sitting at an intersection, it almost always shows my position on the other side.