[AT] Re Driving to Unionville Missouri

[Steve W.]

henry miller wrote:
> Maybe the military GPS is better, but the worst civilian ones are
> still plenty good. When google earth shows you are at the house next
> door that might be GPS - everything farther away than that is bugs in
> google earth. Google's maps contain a lot of errors, and they don't
> seem to be doing much to fix them. Most of the time they will get you
> close, but that is the most you can ask. You will often have to drive
> around a bit to find where you you want to be.
> 
> I work with precision GPS, we can get you within 1 inch of where you
> want to be. But that doesn't stop us from trying to get you to 1 inch
> of the wrong house.


The reason the MIL spec ones are "better" is generally because they 
cheat. They don't use only the GPS satellites. They receive the WAAS and 
DGPS correction information as well as using signals from local fixed 
beacons set up using GPS and compass information.
When the system is working correctly it will put you within 1" of your 
target 99.9% of the time.
Then you have MUCH better cartography on military maps as well. They use 
aircraft and ground equipment to mark all the roads and buildings using 
the GPS system.

On the civilian side you have cartography based on maps that may not 
have been altered or updated for 20 years. Road names change, roads 
become seasonal or closed or relocated. You can see this real easily in 
Google maps and Bing, although Bing seems to update more often. Google 
relies on people who spot something wrong to edit the maps. You also 
have intentional errors introduced by cartographers. They will add a 
road or change a detail of a road in a way that they can prove the error 
is intentional and copywrite protected. Now add to that the errors in 
the mail service address systems and the measuring errors for 911 
addresses. They start the numbering at State, County, City. Town, 
Village lines. but some of those are based on wrong locational data or 
instead of using the actual line location found through GPS they use the 
signs that the localities installed.

Now with the internet and good GPS and local data most of this could all 
be corrected, However there are many folks who don't want it corrected 
for whatever reason. I try to keep the local stuff correct because it 
comes in handy for FD calls. Much easier when you know where you're going.


-- 
Steve W.