Exactly how GPS calculate routes?

I think they have turned the routing over to the preschoolers at the local daycare. They can't even get on the sidewalk without someone holding their hand.

Next to the software problems, routing is my biggest complaint. I'll definitely look long and hard at a Tom-Tom when I think about a replacement.

No more Garmin now !

Newer maps come with more information... sometimes a speed limit intstead of merely a road classification.

If your the new info implies the off-highway route is faster than the highway route... well, there you go.

In Minneapolis, between Plymouth Rd and Minn-100, my 765 alternately chooses I-394 and Minn-55 depending on which way I'm going, where I'm actually starting from, and of course, traffic conditions.

Both have a 55mph speed limit. Stop signs and stop lights aren't part of the equation, so the obvious highway choice is actually "equal" in both time and distance (as close as I can tell) to the surface street choice.

Good luck with that. As you can see from my sig I have both and would take the Nuvi's routing 9 times out of 10. Rarely do they calculate different routes and when they do the Garmin is usually a better choice.

Your mileage may vary.

I have the same problem. The route that my Garmin chooses is one exit north of my preferred and shorter route home. However, as soon as I past the Garmin chosen exit, it recalculates the route and plots my preferred route. I guess in your daily region you must rely on your own shortcuts and make your own decisions.

The Garmin plots my route home from work on a surface street clogged with traffic and lights and aggravation when about a mile due south there's a parkway that follows the same route, more or less... I followed it's route once... ONCE! From now on I let it recalculate from what I know to be the better route. When traveling and I'm clueless, I'll do the goofy driving. At least I won't know.

I notice that garmin takes the roads where speed limits are listed on their programs. I use an old country road that diagonals between two points and garmin will alway take the two perpendicular roads because the diagonal road doesn't have a speed limit posted but the perpendicular roads do have speed limits. So I just let Jill "recalculate" for 10 minutes or so as I note that my arrival time drops about 4 minutes using the diagonal road.

My garmin units sometimes take me different ways in spite of leaving from the same place and going to the same destination.

Since I know how to get home I never use my Garmin for routing when I drive around locally. I do leave it on for the map and occasional red light camera warning. I have found when I am going to a new place it always gets me there and since I am unfamiliar with the trip I have no way of knowing if it was the best route. All I know is that it is faster than asking for directions and getting turned around.

My 1490t, sometimes, does the same thing. Once, I didn't listen to "Emily" and found myself in a massive traffic jam. I haven't had this thing for a long time but, so far, I find the traffic feature is accurate about 75% of the time. Time will tell...

I follow the same logic.
I like a feature that some Magellan models have where GPS calculates a few different routes (shortest, fastest, least fuel) at the same time and lets you chose one once times and distances are presented to you. This makes much more sense and I really wish my Nuvi has this feature.

I'd have to agree.

Why in the world do you care how it routes you home in your own town where you ought to already know how to get home? I can't imagine using the nüvi "just to use it" when I don't have any logical reason to have it running. I know how to get around my own town. I don't need a GPS to tell me how to get home from work.

I like that feature. Why can't Garmin have something like that. Maybe my next GPS will be a Magellan.

I bought my first handheld GPS for hiking about 15 years ago. Back then a feature called Selective Availability was being activated by the US military to prevent the average citizen ( or terrorist) to have the same accuracy as the military GPS systems.

It was only about 10 years ago (May 01 2000) when SA was removed and GPS's became accurate enough for automotive use.

It was only about 5 years ago that GPS's became affordable to the average person. So there is a good chance that most people on these forums never owned a GPS 5 years ago.

When I started my job 30 years ago it took weeks of trial and error to find the quickest way home. In fact after 30 years of working in the same location, my routes home have changed many times as the city has grown.

Now these people expect their new GPS to know their favorite route home right out of the box. And if they find another favorite route they will expect their GPS to discover it the same day.

Let me tell you that after 15 years of using a GPS I am still amazed everyday time I use it. I am amazed that this little box knows about every city, street, and address (almost) in North America. The fact that it can tell me how to get there at all is incredible.

A GPS is so much easier and safer to use than a paper map, that I will never complain that it doesn't take me home the same route I happened to discover last week.

This discussion reminds me very much of this video
http://www.youtube.com/watch?v=rOtEQB-9tvk

Rick

I have said this before, but I have been on a rout that there is only one way to go. (all the exits between the begining and the end of my trip only go into farming areas) There is no other way to go! My GPS keeps telling me it has a better rout. It askes me if I want to go that way. Once I said yes, it would start to recalculate and give the same way it did from the begining.

But if you use the GPS regularly the battery stays charged. Put it away and the battery might not accept a charge next time you need it.

I love that clip....

My Nuvi 200 will sometimes calculate different routes to two destinations that are both on the same highway, in line with one another. To make a long story short, I can have two destinations with a common path of travel for the first 30+ miles. The Nuvi will sometimes route me one way, and sometimes another way, from my house to a common point near the beginning of the trip. From that point on, the two routes are identical (except one may be a few miles farther along the same road). I think there would be one preferable way to reach that common point, and it shouldn't vary depending on how far I'm going beyond that point, especially if all the remaining travel is in a straight line on the same highway.

I have 1490t and am perplexed at the routes it plans--even with avoidances turned off.

I use it in my town too so I can avoid traffic if need be, use the bluetooth (which sounds bad on the other end). I also use in in town just to find out how well it can do it's job in an area I know. This way I can wonder how many odd routes it takes me on out of town. Given the paths taken where I know, I'm not sure I want to know what it does when I'm out of town.

When I come home it wants to take in down Dixie Hwy filled with traffic lights as opposed to free flowing expressway. In another route it literally drives me past my house on an expressway to bring me in the back way--instead of the shortest and fastest (not a cool short cut I just found)--but off a large highway that is old as dirt and should be common sense. I think it is wanting to avoid a left turn across traffic--but there's a light so it's no problem.

I have to say this. I've tried TT, Magellan and the Garmin, and was impressed with the routing of the Magellan the most. It taught me better ways in my own town that I never thought of. Might be going back.

I too am amazed at what GPSs can do. Boggles my mind. But I'm not asking for a GPS to know a "favorite" or top secret route just discovered by the NSA--just the common sense one that any goof would choose looking at any (dated) paper map--and certainly not take me past and around my house to bring me in a goofy back way that is neither shorter or quicker. I miss the logic or science on such routes.

I found that Magellan must use the routing of NAVTEQ.com, and Garmin uses those similar or identical to Google. Try some paths and notice the difference. (Interstate trips are going to be the same as you can imagine. Though going through Nashville Magellan goes the correct way.) Some NAVTEQ/Magellan paths in town may seen silly but actually are a great plan. I've learned a few good paths where I live.

It's possible other GPS do some routes better than others in different areas I'm sure. But where I've traveled and from from my experience the NAVTEQ/Magellan routes are very clever and make good sense in the areas I know. That leads me to conclude that the same would hold true in other areas as well. It has in the ones I've been in.

I don't mean this as a slam on GPSs--I just don't understand the odd things they do at times. They likely can't figure me out either.

That video was very funny. I agree with your post.