Jerky

Navi: Calculating Time to Destination, does it calculate your speed?

Say you're traveling to your destination on the freeway and you're going 50 miles per hour. all of the sudden you hit massive traffic and are now going 10 miles per hour

does the navi calculate that into your desitnation time?

TLNJ

Someone correct me if I'm wrong, but I don't believe it does.

I've seen some navigation systems in your example when you hit traffic change based on your speed. Say you have 50 miles to go and you're traveling @ 50Mph and slow down to 10 Mph it'll change from 1 Hr to 5 Hrs (time to destination).

Whereas our Navi just stays at 1 Hr...I guess ours assumes a constant speed.

Jerky

That's my assumption as well, anyone else have any clues?

cM3go

it does as long as you are not stationary... I have seen the clock go up, based on the fact I am going slower.

vtec1jk

I assumed it took the average speed from the MID and caluclatd by that

Pankul

I agree, I have had times when I am stuck in NYC traffic, and Navi does not update time If am I just stopped, however once i Move, it updates time approx

6mtV6

The navi does calculate the time to destination. A few times when I was stuck in traffic or moving slowly, the time to destination goes up. When I speed up, the time to destination decreases. It takes a few minutes to recalculate.

Jerky

Oh wow, so it does change the estimated duraction by calculating your speed!!!

bluenoise

I thought it was calculating estimated time based on the speed limits along the planned route. Maybe it just does this for the initial calculation before you drive off. For instance, if I'm sitting in my garage and I've just started the car and entered a destination, it comes up with a time estimate. I've never noticed if that estimate is adjusted once I'm in motion according to my actual speed.

jafo

I believe most in-car (built-in) nav systems recalculate based on vehicles speed trends. Most cheap handheld GPS devices do not.

Kubrus

When i drove cross country i tested this -- it seems it does NOT calculate by speed, but by speed limits of the roads you travel. Case in point -- going 80 mph and 30 miles to go, it still said i had 30 mins left in the drive.

jafo

The GPS system has no idea about posted speed limits.

spackletoe

Taking this info, Jafo's comment, and my own experience into consideration, I think vteck1jk is correct. I think it takes the average speed from the MID, or at least the average speed of the car since you plotted the trip.

So if you're on mile 51 of a 100 mile trip, and you've been going 60 MPH the whole way so far (your average is 60) the car will base the time you hav left on that average, even though you may be going 80 on mile 51. It'll still read that you have 50 minutes left til your destination until you get that average up.

This is still just a guess, someone's got to know for sure, but this guess makes sense based on all my trips the last 4 years.

-spack

rets

Bascially, our Navi is getting lots of info from our Navi DVD Disc, then Navi system use satellites signals to identify each info in the Disc. We're not sure if this Navi calculation is really having any direct or indirect conjunction of technicial or mechanical factors of MID. (I won't be surprised if Acura uses two individual systems to play this trick. Our HFL and Navi voice command systems are two different systems, for instance) But, IMHO, I belive their final outcome are estimated by the similar formula. For example, ppl may find out that sometimes your Miles to Empty has displayed the different info. It calculates your recent average speed and MPH in past dozens of miles, then figure that mileage info with the leftover capacity of your tank.

midas69

This is 'kind of' wrong. While the GPS system doesn't know about speed limits, the Navigation system surely does. That's how it calculates the best route to where you're going.

¿GotJazz?

jafo - while what you said was technically correct (the GPS satellite network knows nothing about posted speed limits), your comment was misleading. The Acura Navi system does know about posted speed limits, and uses them for the TTD calculation. Along with all the ATMs, Italian restaurants, and different strips of roadway stored in the Acura TL Navi database, the known speed limit for all those stretchs of roadway is stored as well.

I have a bit of experience with this topic and Navi/GPS systems in general.

Being an anal-retentive engineer, I wondered about this myself when I first got my 04TL. So, I did some test runs.

From what I have determined, the TL's Navi calculates and updates the TTD display based entirely upon posted speed limits along the selected route. Actual speed/driving habits does not enter into the calculation.

Assuming that you are traveling faster than the posted speed limit on a stretch of highway (you naughty 270 HP TL owner!), you will gradually see the TTD decrease at a faster than real-time rate as you get closer to your destination.

For example, if your trip is exactly 65 miles of entirely highway driving and the highway speed limit is 65 MPH, the TTD display would be 1:00 (exactly one hour). However, since your momma didn't bring you up right, you average around 90 MPH for most of the trip.

What you will see on the Navi display will be the TTD decreasing at a faster rate than 1 minute for every real minute of time that passes. This is due to the Navi recalculating the amount of time left based upon the remaining distance divided by the posted speed limit. Your remaining distance is going down at a roughly 31% faster rate than the Navi would have calculated.

After 15 minutes of 90 MPH driving have passed, you would have traveled 22.5 miles. The Navi would show approximately 0:40 minutes to destination (39.23 minutes rounded up). If you went 65 MPH the rest of the way, your total trip time would be approximately 0:55.

After 30 minutes of 90 MPH driving have passed, you would have traveled 45 miles. The Navi would show approximately 0:19 minutes to destination (18.46 minutes rounded up). If you went 65 MPH the rest of the way, your total trip time would be approximately 0:49.

After 42.67 minutes of 90 MPH driving have passed, you would have traveled 64 miles. The Navi would show approximately 0:01 minutes to destination (0.92 minutes rounded up). If you went 65 MPH the rest of the way, your total trip time would be approximately 0:44.

If the Navi updates the TTD once a minute (I haven't figured out how often it really updates yet), you might see the TTD display drop by more than 1 minute occasionally due to rounding/quantization errors.

There are better systems for calcuating TTD. One easy option that I saw allowed the user to enter their "real speeds" for different types of roadway (superhighway, city streets, rural highway, neighborhood streets, etc.). For example, the default value for superhighways would be 75 MPH, but you could enter 80 MPH for superhighways and TTDs would be calculated using your entered value. This would require the Navi database to store the type of roadway along with the speed limit (which it probably already does).

Another option would be to store rough "driving habits". This is a lot more complex. To work properly, it would need to key off of the Driver 1 or 2 information when you unlock your doors. The Navi would calculate your average speeds for different road types, and auto-fill the values described in the paragraph above.

There are even more complex methods than that one. I won't get into it, since it doesn't really matter anyways.

Anyways, hopefully you have a better idea of how the Acura Navi calculated TTD now ...

spackletoe

Great post, but it sounds like you contradicted yourself with these two statements. If the car bases the TTD entirely on posted speed limits, then how does your second statement hold true?

It's got to be a combination of the two, right?

The fact that it won't modify the TTD when you're sitting still is a great feature, but it's got to get the initial estimate for your TTD somewhere. So saying that the navi knows what the speed limits are may be accurate, or maybe it just assumes 60 MPH the whole way to get this time. Then there's the fact that it modifies the TTD along the way, something that wouldn't happen if all it based its estimation on is speed limits. It's GOT to take your current speed/past speeds into consideration.

I'd love to know the exact formula. We could speculate all day. (I think we have).

-spack

bluenoise

Actually, there's no contradiction. The system is continuously recalculating the remaining time based on your current distance to destination and the speed limits along the remaining route. The fact that you're closing on your destination faster than the posted speed limits dictate means that the recalculation appears to reflect your speed.

spackletoe

Okay, so it's not taking your speed into consideration, but your location.

Pretty sneaky, sis!

-spack

¿GotJazz?

Exactly. I guess I wasn't totally clear on that (though I tried). That's also why the TTD doesn't go to infinity when you are sitting still.

I will ammend my previous statements with some additional information. The Navi may not use posted speed limits for each type of roadway, but use an average speed for that type of roadway instead. For example, a 65 MPH stretch of highway might average to 58 MPH when you include gas stops, potty breaks, and restaurant visits. A downtown city street may be posted at 40 MPH, but the same stretch might average 31 MPH when you include stop lights, potty breaks, and traffic congestion. If these same speed averages were applied to similar road types across the US, you would see a much higher TTD value than you would expect.

I'm very sure (95%) that I have told you how TDD is calculated on the TL Navi. I just don't know the exact values being used in the equations.

Might be interesting to test some day if I can find a few good candidates for trips.

silverbishop

Just to add my own experience on the above (and my really high statistics):

i. IF car_speed >= posted_speed_limit THEN Navi calculates time left by using the posted_speed_limit. You will actually notice that time left drops faster than actually time.

ii. IF car_speed < posted_speed_limit THEN Navi calculates time left by using the car_speed.

Navi uses the instantaneous speed of the vehicle, when it refreshes. Refresh time varies according to the speed of the vehicle (faster it travels, sooner it refreshes).

Pankul

Quite sophisticated huh!

¿GotJazz?

Odd. I didn't see my TTD go up when I'm going less than the speed limit (I tested it today), and I definitely haven't seen the TTD go to infinity while sitting still (TTD = distance/MPH, which when standing still would be distance/0).

Can you cite any examples of how you saw this happen?

silverbishop

Certainly it never goes to infinity (it is just a computer..., you should expect to see an error, not infinity), but sometimes when you stay for long still, it may show some strange time (I have seen something like 1260 hours indications, the error that I said before). On the other hand it is smart enough to know when you are standing still, and then doesn't refresh the speed stored in the memory, but keeps the last saved one. If you roll (like when you are stucked in traffic), then it is another story.

The algorithm is not that simple as I described it (I just tried to give a first order illustration of how it works). Actually the rates that it refreshes are quite different, plus the fact that keeps in memory (and in calculation) an average speed (I can check, but if I recall, must be ~15-30 minutes). Much longer than what MID keeps in memory.

PG2G

This weekend I was stuck in traffic and figured I would pay attention to the navi to see what it said. Even as I was inching closer to my destination, at speeds ranging between 0-15 mph, I noticed that the time to arrival increased. So I don't think it is purely distance divided by speed limit. Also, it sure doesn't sample car speed at a point in time, as it would have been pretty obvious that a 90 mile trip was going to take me longer than an hour and a half when I was driving 10mph. There was also no drastic change when I got out of traffic, but it did drop a little bit.

Meh, who knows :P

cardoc

The GPS calculates speed over the ground almost as well as a speedometer. In my many years of racing sailboats, where it felt like we were FLYING if we made 15 knots (~18mph), the GPS could be counted on to calculate arrival time. If you went slower, the arrival time was later, and conversely.

I doubt that our cars have differential GPS, but perhaps they do, and that increases accuracy considerably.

Dr. Bill Miller St. Louis

Brewmaster

GotJazz .. nice to see you back ..

I'm with you, I think your ammended posting which indicates the use of average speeds on certain roads or road types is closer to how our systems work. GPS for position, NAV info for distance to travel and average road speeds, updated periodically for TTD ..

Well done

jskoog

The manual states that the time to completion is based upon the posted speed limit of the highways on the route (taken from the navigation info on the CD). This was my bigest disappointment with my TL, since I'd just spent 4 years in a BMW M5. The nav in that car continually computed and displayed ARRIVAL TIME based upon how fast you were going, and was pretty good at predicting how long a trip would actually take. When stuck in traffic you would see a 30 minute trip turn into 2 hours! And a 4 hour trip might show 2.5 hours under the right conditions .

Jim

Jerky

Jim

why did you leave the m5 for the TL?

That's the car Im aimed at...

jskoog

Basically it was the cost of operation. The warrantee was up, and the good tires that the car needed worked out to be $100/month. (about 11,000 miles per set) Around town I got about 13.5mpg. It was a dream car, the one I always wanted. I was tempted to buy an older m5, but when the new one came out in 2000, I ordered one. It was my retirement money, before I retired. Now I won't be able to....

But well worth it. And the new one has 500HP...

Jim

Silver Bullet

Sorry for posting so late on this topic.

I finally figured out driving from Dallas to Denver that Navi always calculates based on 55mph. So time to destination is calculated on that equation. If you are going faster or slower the time will always adjust, based on 55mph. If you are going faster than the distance will reduce quicker but the time to destination will always be calculated based on 55mph. Same if you are going slower.

That's the easiest way to explain it.