How do I do a tracklog if I am in a tunnel?

[FrancisTLim]

I guess the best is to drive into the tunnel from both directions and take the last satellite reception points at both ends. Then draw a straight line joining them both should be fine, right? Since users of the resultant map will not have reception on their GPSR while in the tunnel anyway, their GPSR will not be giving them any guidance while they are in the tunnel, so it does not matter that the two points are joined by a straight line, right? Just wondering if anyone have any thoughts on whether there is any advantage of having a real track instead of just a straight line. Hope to hear from you.

[JasonLee]

I guess the best is to drive into the tunnel from both directions and take the last satellite reception points at both ends. Then draw a straight line joining them both should be fine, right? Since users of the resultant map will not have reception on their GPSR while in the tunnel anyway, their GPSR will not be giving them any guidance while they are in the tunnel, so it does not matter that the two points are joined by a straight line, right? Just wondering if anyone have any thoughts on whether there is any advantage of having a real track instead of just a straight line. Hope to hear from you.

For the purpose of not losing satellite lock, a straight line is too short if the tunnel is actually a curve. This is because in a Garmin compiled map, the GPS goes into a simulation mode when it encounters a tunnel coded as such and if the car maintains the same speed as the entry speed then it will not lose satellite signal if it does not take more than x seconds. However, if the tunnel is drawn straight instead of a curve, the car will emerge in more than x seconds based on a shorter straight tunnel whereas in reality the tunnel is longer and curved so you need more time. I am sure in such a case it will lose satellite lock. Conversely if we draw a curved tunnel for a straight one, the GPS will assume it is still in the tunnel for x seconds so the tracklogs will not be accurate if it is still in a simulation mode. Hence it is better to be accurate.

I agree for cgpsMapper compiled maps, it does not matter and you are going to lose satellite lock anyway. How soon you will regain satellite lock on emerging the tunnel will depend on the capability of the GPS.

[ace]

I guess the best is to drive into the tunnel from both directions and take the last satellite reception points at both ends. Then draw a straight line joining them both should be fine, right? Since users of the resultant map will not have reception on their GPSR while in the tunnel anyway, their GPSR will not be giving them any guidance while they are in the tunnel, so it does not matter that the two points are joined by a straight line, right? Just wondering if anyone have any thoughts on whether there is any advantage of having a real track instead of just a straight line. Hope to hear from you.

For the purpose of not losing satellite lock, a straight line is too short if the tunnel is actually a curve. This is because in a Garmin compiled map, the GPS goes into a simulation mode when it encounters a tunnel coded as such and if the car maintains the same speed as the entry speed then it will not lose satellite signal if it does not take more than x seconds. However, if the tunnel is drawn straight instead of a curve, the car will emerge in less than x seconds. I am not sure in such a case it will lose satellite lock or not. Logically thinking, the GPS will assume it is still in the tunnel for x seconds so the tracklogs will not be accurate if it is still in a simulation mode.

I agree for cgpsMapper compiled maps, it does not matter and you are going to lose satellite lock anyway. How soon you will regain satellite lock on emerging the tunnel will depend on the capability of the GPS.

Bro Jasonlee, for Garmin generated maps, confirmed your GPSr will tell you that it has "Lost Satellite Connection" if based on your entry speed, you did not emerge from your planned route out of the tunnel at the estimated time that you are supposed to log back fresh to the satellites. The estimation is quite accurate if you can maintain the same constant speed as your entry speed. If the tunnel are properly drawn, the GPSr will inform you as you approach your exit in the tunnel, much like what you will hear on the surface road. So the concept of drawing a straight line between the two exits are not advisable especially tunnels in Singapore, which tend to curve quite a fair bit due to the obstacles in its path above ground.

[FrancisTLim]

For the purpose of not losing satellite lock, a straight line is too short if the tunnel is actually a curve. This is because in a Garmin compiled map, the GPS goes into a simulation mode when it encounters a tunnel coded as such and if the car maintains the same speed as the entry speed then it will not lose satellite signal if it does not take more than x seconds.

I agree for cgpsMapper compiled maps, it does not matter and you are going to lose satellite lock anyway. How soon you will regain satellite lock on emerging the tunnel will depend on the capability of the GPS.

Thanks on that info about Garmin compiled map. In that case, also take note of the distance (from car odometer) and then draw some random curve to make up that distance.

[JasonLee]

Thanks on that info about Garmin compiled map. In that case, also take note of the distance (from car odometer) and then draw some random curve to make up that distance.

Dear Bro Francis,

That makes more sense than drawing a straight line so the simulator will have the correct distance to simulate however wouldn't it make the mapper appear silly when later on the publshed map shows a bend to the right when the mapper's random curve bends to the left?

[moeyhc]

What if there are exit junctions or split roads inside the tunnel?... How ah?...

It doesn't matter isn't it.... You Are Lost!... so, before you enter any tunnel do check your route and be prepared for it. The GPS will not work... please use a paper map...

[FrancisTLim]

..however wouldn't it make the mapper appear silly when later on the publshed map shows a bend to the right when the mapper's random curve bends to the left?

I have not seen the simulation mode, but I would think it will clearly show that it has lost satellite reception and is in simulation mode, right? Then the user will know that the bends may not correspond.

What if there are exit junctions or split roads inside the tunnel?... How ah?...
It doesn't matter isn't it.... You Are Lost!... so, before you enter any tunnel do check your route and be prepared for it. The GPS will not work... please use a paper map...

Not necessary to use paper map lah. Even without satellite reception, I prefer to use GPSR map because I can zoom in to check details.

[JasonLee]

I have not seen the simulation mode, but I would think it will clearly show that it has lost satellite reception and is in simulation mode, right? Then the user will know that the bends may not correspond.

No, you will not see any difference. It will be as if you still have satellite lock and your car icon will continue to travel along the road in the map (as long as you are in the simulation mode). If you are too slow to emerge then your device will announce "lost satellite reception".