Question about GPS (Anchorage, Wasilla: manufacturing, design, rating)

[rotorhead]

I suspect it's mostly a matter about money, of course. GPS works fine up here, I use a handheld Garmin loaded with nautical software that holds an incredible amount of data, and is dead-on. When it comes to getting the street locations right, it's another matter though. My unit that has every light, beacon, submerged rock, and millions of depth readings is hopeless once it reaches shore, even the major streets are way, way off.

The automakers want to use one software mapset for every car they sell, it would be a big hassle if they had to load separate software for every region they sold cars in. As it turns out, those "all purpose" mapsets are hugely biased towards the big cities down south. Most of the ones I've seen have every subway sandwitch shop in NYC, but a lousy, virtually unusable level of detail for anything outside the large urban areas. Up here in AK we might as well be on the moon, as far as they're concerned. There's just not enough people up here and enough road miles for them to get serious about improving their accuracy. It wouldn't surprise me at all if they'd made a total rookie mistake like using the wrong datum for all the Alaska roads, resulting in them being way, way off.

I've used a Garmin IQue PDA/GPS up here in the past that had some fairly accurate road software loaded, but it wasn't the mapset it came with, that was lousy. I can't remember which one it was, it was a few years ago. In any case, if you buy the GPS pre-installed in the cars dashboard, you're almost certainly stuck with it's generic map software, which is usually hopeless up here. With a handheld model, you can choose your own maps, which usually works better.

[Moose Whisperer]

Originally Posted by Glitch

Your Garmin was probably already set to NAD27, which is the datum used by the older USGS maps. If it was set to the latest datum standard, WGS84, then the roads on the USGS map would appear to be off by more than 100 meters in Anchorage, and even worse in Fairbanks.

Even though my Garmin displays its position very accurately on the map, I just wanted to be sure so I checked and found it is set to WGS84. In fact, all Garmin’s come from the factory set to the WSG84 datum by default (I have a 60CSx). This also matches the USGS Topos, which also use the WSG84 datum, so all is well!

[rotorhead]

The problem is not the GPS system, it's in the mapping software they use. If the original data was digitized using the wrong datum, it's always gonna show that you're off. Your actual position will be correct by lat/long, but the display will show the road elsewhere. In a place like NY or LA they's have so many people complain about it that they'll do something to fix it, but even if everyone in AK owned one and bitched about it, it still wouldn't be enough for them to spend the money to fix it.

[Glitch]

Originally Posted by AK_Photographer

Even though my Garmin displays its position very accurately on the map, I just wanted to be sure so I checked and found it is set to WGS84. In fact, all Garmin’s come from the factory set to the WSG84 datum by default (I have a 60CSx). This also matches the USGS Topos, which also use the WSG84 datum, so all is well!

You must be using updated USGS maps then. The vast majority of the USGS quadrangle maps were made in the 1950s and use NAD27. Either way, the maps will include the horizontal datum they used and the GPS can be set to the same datum. But if this isn't done, then the map will not match the GPS readings.

[Glitch]

Originally Posted by rotorhead

The problem is not the GPS system, it's in the mapping software they use. If the original data was digitized using the wrong datum, it's always gonna show that you're off. Your actual position will be correct by lat/long, but the display will show the road elsewhere. In a place like NY or LA they's have so many people complain about it that they'll do something to fix it, but even if everyone in AK owned one and bitched about it, it still wouldn't be enough for them to spend the money to fix it.

I agree. GPS' work perfectly, you just can't trust the location of the map objects they have loaded. GPS' are still much easier to use than compasses because you don't have to worry about the location of magnetic north.

As far as using a GPS to navigate, if you use them to locate waypoints you have already established, they are marvelous. They are great for showing you where you have been. Using them to locate someplace where you have never been is another story.

[Moose Whisperer]

Originally Posted by Glitch

...Either way, the maps will include the horizontal datum they used and the GPS can be set to the same datum. But if this isn't done, then the map will not match the GPS readings....

Originally Posted by Glitch

I also own a Garmin GPS...However, it also shows me driving through the middle of Knik Arm when the map is displayed...

So, it’s simply a matter of resetting your Garmin to the appropriate Datum.

[warptman]

Just don't get lost...

[Alaskapat528]

Originally Posted by AK_Photographer

The ongoing discussions about direction finding and survival skills reminds me of an off the wall question I have. Does anyone know why new cars sold in Alaska aren’t available with factory navigation systems? All the salesmen keep telling me it’s because “GPS’s don’t work in Alaska.”

Huh? My Garmin works just fine, all the way up to Prudhoe. What gives?

My husband has a Magellan GPS and it works fine here in Alaska.

[Glitch]

Originally Posted by AK_Photographer

So, it’s simply a matter of resetting your Garmin to the appropriate Datum.

Not so simple when the built-in internal map is wrong. I can set the correct datum for external maps, but I have no idea what datum was used for the internal road map that came from the factory.

[Moose Whisperer]

Originally Posted by Glitch

Not so simple when the built-in internal map is wrong. I can set the correct datum for external maps, but I have no idea what datum was used for the internal road map that came from the factory.

Not knowing the correct datum does not mean that the map is “wrong.” Rather, it simply means that you have not properly set up your GPS to accurately display its position on the map.