TomTom Navigator 5 - US Map Accuracy?

levman · Occasional Visitor Joined: Jul 21, 2006 Posts: 18

I've had Navigator installed on my Treo for about a week now ... have navigated to about a dozen different spots in two different states (Columbus, Ohio and Denver, Colorado) ... and in each case, TomTom reported the destination as being between 1/2 mile and 1 mile beyond where it actually was. I know that TomTom is reporting my location on the street correctly, at least if I watch the screen as I pass cross-streets it reports my location accurately; and if I mark a POI by GPS position I can navigate to that successfully as well. But if I try to navigate to a street address - any street address, it appears - Naigator thinks that the address is well beyond where it actually is. Has anyone else experienced this with the US maps? Could Navigator be having problems converting addresses into lat/lon positions?

jgombos · Regular Visitor Joined: Jul 25, 2006 Posts: 87

I believe it's the inaccuracy of the address numbers that you're observing. If you browse to the Dry Dock Inn in Sugar Grove, OH, TomTom is off by a whole block - yet TomTom has the correct address. So it seems the address numbers are often shifted out of place.

elyl · Posted: Thu Jul 27, 2006 10:12 pm Post subject:

Yeah, TomTom tries to guess where a house number is on a street just by dividing the street up mathematically. As you can see, this doesn't always work very well if certain house numbers are not used, or there are differently-sized houses or blocks.
I did notice, however, that some streets in the US, the house number was precisely where it said it was in TomTom (i.e. more precise than you would imagine from an interpretation), which makes me think that the maps sometimes contain precise house number info, and sometimes not.

levman · Occasional Visitor Joined: Jul 21, 2006 Posts: 18

mikealder · Posted: Fri Jul 28, 2006 1:46 am Post subject:

As the POI file only contains the Lat/ long and name it should be more accurate, however the information contained in the POI file needs to be accurate to start with Wink

if its out by a fair distance you can't blame the device, it is only taking you to that supplied location, or the nearest known road to that location it has within its currently loaded map (some POI locations can be "off road" so ithe unit will get you as close as possible via a road it knows of - Mike

elyl · Posted: Sat Jul 29, 2006 1:11 am Post subject:

Business locations will likely have been interpolated from their address details in the yellow pages, for example. The precise location of each business will not have been determined, just the worked-out position from the address.

levman · Occasional Visitor Joined: Jul 21, 2006 Posts: 18

What troubles me is how consistently inaccurate the POI positions seem to be. I have been using TomTom to navigate to places that I've successfully navigated to with three different GPSs (Pocket CoPilot, Hertz Neverlost, and the GPS in my Chrysler minivan) and, while I don't expect the navigation to always be perfect, I have never experienced this level of incorrect POI location information. I've navigated to at least a dozen locations in two states with TomTom, and while TomTom always gets me on the right road, the POIs are always off by at least a few blocks and often more than that.

I suspect this has to do with whatever algorithm or company they use to do their geocoding of addresses to lan/lon positions. Just for grins, I tried putting a few of the addresses I've navigated to into Mapquest, Google Maps, and Geocode.com. Geocode.com is run by Tele Atlas, which I believe is the same company TomTom uses for its geocoding (see http://www.teleatlas.com/Pub/Partners/Success_Stories/index.htm ). Sure enough, the addresses showed up where they should be in Mapquest and Google, but on Geocode.com they were showing up further down the road than they actually were, and in the same (incorrect) locations that TomTom was navigating me to.

I've come to really like TomTom, other than this very annoying problem ... but now I am wondering if I should try some other Palm-based Nav software.

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