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How is Time to Destination Calculated?


CiscoHiker
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Can some one explain how the time to desination is calculated? I have been using my 60CSx of late to route to different places (using the city select software loaded on a 60CSx). It seems to be more intelligent calculation than just using the current speed and total distace. Does it look at the roads ahead (ie a interstate vs a dirt road)? Just curious on how it makes this calculation.

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Can some one explain how the time to desination is calculated? I have been using my 60CSx of late to route to different places (using the city select software loaded on a 60CSx). It seems to be more intelligent calculation than just using the current speed and total distace. Does it look at the roads ahead (ie a interstate vs a dirt road)? Just curious on how it makes this calculation.

 

If you have Cit Nav maps in, it uses a preset speed for each road type. If you are using another map or no map, it uses speed and distance.

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When auto-routing: It uses preset speed data for each road type based on the type of vehicle that you have assigned in the routing preferences.

 

When routing off road: It uses a running average of closing speed to the destination.

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When auto-routing: It uses preset speed data for each road type based on the type of vehicle that you have assigned in the routing preferences.

 

When routing off road: It uses a running average of closing speed to the destination.

 

Do the speeds you can set in the options in Mapsource get transferred to the GPSr as preset speeds?

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When auto-routing: It uses preset speed data for each road type based on the type of vehicle that you have assigned in the routing preferences.

 

When routing off road: It uses a running average of closing speed to the destination.

 

Do the speeds you can set in the options in Mapsource get transferred to the GPSr as preset speeds?

 

AFAIK, no. The speed settings in MapSource are only to assist with route planning within MapSource. I have changed it numerous times, and when I upload and plan a route, it gives the same roads and same arrival times as always.

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Several answers, nearly all wrong.

 

Garmin's autorouting navigators keep track of how you drive on the eight different road categories that are in the maps. These categories range from high-speed freeways, like the German Autobahn, down to ferry lines.

The speed memory is slowly updated, by some sort of moving average algorithm, as you drive. This means that the more you use your unit in your vehicle, the better it will be at estimating when you'll arrive at your destination.

This also implies that if you start towing a trailer, for example, if may take 50 km or so, for a certain type of road, before it has learned that you are going a bit slower than normal (now assuming that's the case, but in many countries at least the law says you should). Many users don't realize that they have to keep the GPS on, when going by ferry, to let the unit learn how fast a ferry really moves.

 

When the unit is new, it uses the default speeds for the different roads. You can see five of these if you set Mapsource to the default speeds. These speeds are also used when computing the route in the first place. The learned speeds are used for the ETA only. If not, the routes would be inconsistent from one day to another, in many cases.

The speed setting in Mapsource is local only. It's not transferred to the GPS. You can't even change all eight of them. Mapsource needs these settings, as it can't learn how fast you drive.

 

If you use the GPS in simulation mode, you can see the speed it has learned, as the simulation uses that on the road type at hand. You can compare with a friends GPS to see if he drives faster or slower than you do.

Also, if you let the kids borrow the car, GPS included, and your commute to work then suddenly is ten minutes faster, you ought to check how they are driving!

Edited by apersson850
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I can't corroberate apersson's info, but it does square with my experience when I 'follow roads' along a route.

 

When off road (particularly on an airplane), the unit seems to take distance divided by the closing speed to destination (which is not the same as your ground speed, unless you happen to be flying straight at the destination).

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Several answers, nearly all wrong.

 

<snip>

 

If you use the GPS in simulation mode, you can see the speed it has learned, as the simulation uses that on the road type at hand. You can compare with a friends GPS to see if he drives faster or slower than you do.

Also, if you let the kids borrow the car, GPS included, and your commute to work then suddenly is ten minutes faster, you ought to check how they are driving!

 

Excellent info...as usual.

 

The first few times I used my unit for routing I kind of didn't like how the ETE etc. barely changed when there was a sudden change in speed - like stoplight, traffic jam. I kinda thought 'that sucks - how arrogant a GPSr to assume how fast I WILL be driving'. But after watching the 'Time to next' and 'ETA at Destination' numerous times I give in to admitting this method to be far more useful...and, indeed, accurate. I am amazing at how the unit predicts my arrival on a two hours trip to within a minute or so from the start point.!

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