nuvi 3597 went nuts last night

... just a poor GPS signal for a short period

Every one of my units seem to go a little wacky once in a while.

Maybe it is gthe signal quality, magnetic interference, or aliens !

But we swim in a sea of electronic signals and unless the problem is recreatable or occurs with some frequency, there's no telling why weird things happen. Temporary signal interference is as good an answer as any.

Nearby 18 wheeler with a GPS jammer to fool his satellite tracking so his dispatcher didn't know where he was?

I've had this happen with various GPSR's over the years including my 3597. Garmin support told me a while back that this error has to do with the "snap to" feature built in to most automotive units. "Snap to" adjusts the location of each satellite acquisition point to form a smooth line on the map following the nearest road. Without this feature, you would see a series of jagged lines parallel to, or crisscrossing the road.

This phenomenon can be seen on a handheld GPS if you zoom in all the way and watch the screen while standing still. A star pattern will appear over time that will eventually look like a splatter painting.

"Snap to" can sometimes be fooled by a nearby parallel road or by a distorted satellite signal. The error can often be cured by rebooting the GPS.

...aliens.

I have seen that on occasion too. I usually clears itself quickly. Not sure of the cause.

As posted above the cause is simply an inaccurate GPS position

One way to get a wrong position which can persist for a short time occurs when the signal from one of the satellites your receiver is using to calculate position arrives at your receiver by reflection instead of by direct path from a satellite. Obviously this means the signal has traveled a longer distance than is assumed in the calculation, and that throws the calculated position off.

I have seen this effect create a position error of hundreds of feet when I had my Garmin GPS V sitting in a porthole of a small ship arriving in a Caribbean port passing by a steel wall in the form of a large cruise ship. Limited sky view restricted by the porthole meant that only four satellites could be received, and one of them was getting to the receiver by bouncing off the cruise ship. The crumb trail made perfectly clear that this led to a stable incorrect position in which our ship was logged as traveling in a nice straight line parallel to its real position but on dry land.

This happens when my 3597 is overheated. Usually by sitting in the sun too long or once by the windshield heater!

Doug.

There are a few places where this happens every time I go there.. The car image does a few loops then settles back. I attribute this to going from one map area to another.. or aliens
And the snap too feature frequently has me driving in a field..

. . .was when a previously saved route on my old 755t plotted a much longer than normal path along the railroad bridge paralleling the 10-plus miles of elevated interstate I was expecting to travel. Even better, at the far end, I was supposed to double back via the same rail line and THEN proceed in the original direction along the interstate. A subsequent turn from E-W travel to N-S for the next 20-plus miles placed me headed northbound on the southbound side of the separated parallel elevated roadways.

That's when I decided to heed the advice commonly offered back then--follow map updates with a reset to factory defaults and restore the saved routes from your backup made prior to updating. No idea whether it's my newer 3597 or improvements to the update process, but am grateful that I haven't had take such extreme measures since switching.

What you describe is a classic case of jammer interference. It sounds as if you were near the distribution area near Jessup and there was a trucker using a GPS jammer. I've had the same issues on I-75 south of Knoxville where the GPS continued to operate but couldn't display the position correctly. As the truck finally got out of the area, the GPS corrected itself.

That's what I posted, Boxcar. I remember now hearing about the area around Jessup. there is a large truck stop there with a Giant grocery distribution warehouse and several others.

That's true but others were going off on tangents that had no bearing on the temporary condition caused by the jammer. I actually pity that driver if they run a regular route. It won't take too long before the FCC comes down on him and they are hit with a 5 figure fine.