LOCATION OFF SINCE THE JAPAN EARTHQUAKE

Yep, I've been noticing some weird stuff happen with my rig lately. Not the Garmin's fault though from what I can determine.

My 1450 was off long before the problems in Japan,telling me the place I was going to was on the left side of the road instead of the right side where it actually was.

The island of Japan moved about 8 feet but the rest of the world moved only about 4 inches off its axis. So unless you are driving in Japan, you will not notice any difference.

Did the axis move 4 inches pole-to-pole, or was it calculated from only one poles displacement?

I can't find the answer to that question.

I was wondering the same...

Eight feet or eighteen feet, a civilian GPS receiver can't be accurate enough to tell the difference.

4 inches (single pole displacement calculation) over 12,500 miles is more than 18 feet...

Two weeks ago I pulled into my drive and then my garage like always but the GPS showed me still in the road. The road is about 100' from my garage. Have not used it to come home since but will try and see if it works corectly next time I get out.

Your math is correct. However it is not relevant to what happened in Japan. This is a direct quote from the Garmin website

How accurate is GPS?

Today's GPS receivers are extremely accurate, thanks to their parallel multi-channel design. Garmin's 12 parallel channel receivers are quick to lock onto satellites when first turned on and they maintain strong locks, even in dense foliage or urban settings with tall buildings. Certain atmospheric factors and other sources of error can affect the accuracy of GPS receivers. Garmin® GPS receivers are accurate to within 15 meters on average.

So no matter how much displacement might have occurred the GPS would probably not detect it.

The axis that shifted was a calculated change of an imaginary line (the Figure Axis) due to the shift of the land mass of Japan relative to the earth. That does not mean that all points on the earth shifted relative to each other.

Think of a person standing while holding his arms straight down along the sides of his body. The person’s vertical line of center of gravity would run from the center of the top of his head down to between his feet.

If the person extended one arm straight out to his side, his center of gravity would move outward toward the extended arm but the distance between his eyes would not change.

Note also that the Earth's center of mass axis is called the Figure Axis and geographical locations are not measured relative to that axis.

NASA says this about changes to the Figure Axis:

"The position of Earth's figure axis also changes all the time, by about 3.3 feet over the course of a year, or about six times more than the change that should have been caused by the Japan quake."

Eight feet seems a bit high. Check out:

http://geocommons.com/maps/57659

On this analysis the maximum displacement is 4.4m (14' 5") - Yikes! but the vast majority of the island(s) moved less than 0.6m (which is still close to 2') Double Yikes!!!

Data from the very clever interactive website above.

While you are at it, check out:

http://demo.erdas.com.au/WebExamples/IWS/jquery/swipe/japan....

Very cool!

I have not had any problems.

I don't think that the shift has had the same effect across the globe.

It is commonly felt, according to the people who live in my area, that we are shiftless.

Gary

here either - everything was exactly where it was suppose to be.

I haven't seen a change on my end neither.

even if there is a change, shouldn't the gps be able to traingulate the correct location by calculating data from the satellites?

the accuracy on these GPS is around 6 meters in the best of times, so 4/18 inches will not make any difference.

Yeah this makes sense, any comment on this you scientist out there...

With three different war fronts going on as I write this, you can bet the Department of Defense (through the Air Force)has already made alterations to GPS space craft orbits. there is no room for error on the military side of the birds, when your trying to destroy Moammar Gadhafi's command and control and other targets with a GPS guided cruise missiles from many miles away.

The orbiting paths of the satellites are monitord by US Air Force monitoring stations in Hawaii, Kwajalein, Ascension Island, Diego Garcia, and Colorado Springs, Colorado, along with monitor stations operated by the National Geospatial-Intelligence Agency (NGA) These mmonitoring stations are the eyes and ears of GPS and monitor satellites as they pass overhead by measuring distances to them every 1.5 seconds. This data is then smoothed using ionospheric and meteorological information and sent to Master Control Station at Colorado Springs. The ionospheric and meteorological data is needed to get more accurate delay measurements, which in turn improve location estimation. Master control station estimates parameters describing satellites' orbit and clock performance. It also assesses health status of the satellites and determines if any re-positioning may be required. This information is then returned to three uplink stations (stationed at the Ascension Island, Diego Garcia and Kwajalein monitor stations) which transmits the information to satellites.

The initial data suggests northeast Japan's Friday (March 11) earthquake moved the main island about 8 feet, according to Kenneth Hudnut of the U.S. Geological Survey. The earthquake also shifted Earth’s figure axis by about 6 1/2 inches (17 centimeters)“This shift in the position of the figure axis will cause the Earth to wobble a bit differently as it rotates, but will not cause a shift of the Earth’s axis in space – only external forces like the gravitational attraction of the sun, moon, and planets can do that,”

I have a Master of Science degree but I am an engineer, not a scientist. However, I will give you my two cents worth anyway.

Yes the gps receiver such as a Garmin can determine the correct latitude and longitude relative to the reference globe it uses by triangulation calculations relative to three or more satellites.

But until the map is updated in the gpsr, it those coordinates would place you at the wrong point on the map ( i.e. it would place you where on the map you would have been had the land had not shifted).

For example suppose you were standing by a radio tower in Japan when the land shifted relative to the rest of the world. After the shift your gpsr would calculate your new coordinates and place you on the map it has stored in it. But now it would show you away from the radio tower instead of standing right beside it. You could see the difference provided the shift was enough to be noticeable within the accuracy of the calculations.

This "error" would remain until the map in your gpsr is updated to account for the new placement of the land with respect to the reference globe.

I agree with the post directly above me. It will have an impact until the Japan maps are updated. But as stated previously and mentioned regarding the location calculation, the accuracy of typical civilian GPS units will affect how big of a deal that is in practice.

I have noticed more "recalculating" even when I don't make a wrong turn???

Sometimes my Garmin recalculates when I even think about making a wrong turn.

I just got back from Florida and a couple of places were off by at least 50 ft. Last December I had marked the position of the houses of family members and when I returned last week they were off, in one case one house that is second to a street corner was off by half a block and according to the Garmin I had arrived. When in the driveway were I had marked it last year the map showed I was in the middle of the street in the intersection.

But I didn't had any problems getting there and finding other places, everything else was were it should, WEIRD...

The variations you are seeing are due to the differences in the accuracy in effect at the time you marked the spots from the accuracy when you returned. The accuracy at any time depends on several things, like how many satellites have been contacted, differentials available, clouds, radio noise, etc. and can vary from a few feet to several hundred feet.

Very interesting!