toneman

My two cents worth regarding mapping location/address number issues:

Re: address number accuracy--try this...plug in an address for a specific location you know does not exist but is within the range of valid block numbers--e.g., tell the nav to give you directions to 101 Main St. if you know for a fact that 101 Main St. does not exist at all, but is within the valid range of 100-200; if it is able to calculate a route to that "exact" location, then that shows that it is extrapolating the street number based on the block range for that street (and perhaps on any existing locations it may have stored in its database), rather than because there is an exact match for that address in its database. For the nav to accurately display the exact location of any given address, it would have to reference a database that cross-references the latitude/longitude for every single valid street address/number--by all means not impossible, but would be painstaking to create/maintain since any specific street address would need to be visually/physically confirmed as to its actual location.

Re: location accuracy of car nav vs. handheld--it is important to note that many/most in-car nav systems rely on a combination of GPS and wheel sensors/gyros in order to best accurately display your vehicle's current location on the map screen, while almost all handheld/portable GPS units rely solely on GPS to display (as accurately as possible) location. While the streets shown on the map are assumed to be depicted as accurately as possible, relative to other streets/landmarks...one has to keep in mind that GPS-based positioning is not done by determining what street you're on, but rather, what latitude/longitude you're at. I mention this because some portable GPS units (like my Garmin iQue 3600) allow you to display your current location either based on the nearest street you're on (if you're on a road, that is) or according to your current GPS-calculated position; this option clearly implies the possibility that the street map data currently in use may not always correspond to GPS-based coordinates--e.g., you can visually confirm out your car window that you're exactly at the intersection of two streets but GPS shows your location on the map display as being a dozen feet short of it--but at a GPS-calculated latitude/longitude coordinate that is assumed to be fairly accurate. IOW--if a GPS-based nav unit is indicating that you're at latitude X/longitude Y, while showing on the map that you're at the intersection of two cross-streets...which of the two data points would be considered more accurate?

Also, I believe quite a few portable GPS units allow you to select/enable WAAS (Wide Area Augmentation System) in order to increase GPS accuracy to as little as 3 meters; dunno if car navs implement WAAS...it might be a bit overkill for vehicles that use speed sensors to aid in plotting vehicle location on the map display.

Now that I've bored you all w/ this long post, I will concede in that it's one thing if the vehicle nav is showing your location to be off by say 100 feet or more...but IMHO nav accuracy isn't that big a deal if we're talking only about a dozen feet or so.

Rickanns

GREAT POST, Tony. Thanks for your time and insight. I am mulling over your points and comparing to previous GPS projects. I will post more later.

Rick

PS - Aren't these forums great for expanding knowledge as well as particular vehicle info and entertainment!