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Math Help - How many seconds from my destination am I?

  1. #1
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    How many seconds from my destination am I?

    Think I put this in the wrong place?
    A mile has 5,280 feet, and an hour has 3,600 seconds, so 60 miles per hour is:
    60 x 5,280 / 3,600 = 88 fps
    (60 mph = 88 fps )

    How to determine how many seconds from your destination you are (example driving in a car and you are 1500' from your next turn):

    1. Determine distance to travel (1500 feet)
    2. Determine speed
    3. Determine feet per second
    4. Determine how many seconds from the destination you are

    Letís say you are 1500 feet from your turn and you are going 30 mph. You want to be notified 7 seconds from the turn.
    30 x 5280 / 3600 = 44 feet per second
    1500 feet / 44 feet per second = you are 34.090909 seconds from the turn

    I can process this every second until I am 7 seconds out. Is that the best method (assuming you could speed up or slow down it would need to be checked/computed every second)

    Looks right to me, but can anyone verify that is accurate?

    Any math experts that can validate this (Just like the old school questions)?
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  2. #2
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    Re: How many seconds from my destination am I?

    Quote Originally Posted by holzert View Post
    Think I put this in the wrong place?
    A mile has 5,280 feet, and an hour has 3,600 seconds, so 60 miles per hour is:
    60 x 5,280 / 3,600 = 88 fps
    (60 mph = 88 fps )

    How to determine how many seconds from your destination you are (example driving in a car and you are 1500' from your next turn):

    1. Determine distance to travel (1500 feet)
    2. Determine speed
    3. Determine feet per second
    4. Determine how many seconds from the destination you are

    Letís say you are 1500 feet from your turn and you are going 30 mph. You want to be notified 7 seconds from the turn.
    30 x 5280 / 3600 = 44 feet per second
    1500 feet / 44 feet per second = you are 34.090909 seconds from the turn

    Okay, that is good.

    I can process this every second until I am 7 seconds out. Is that the best method (assuming you could speed up or slow down it would need to be checked/computed every second)
    What, exactly, are you trying to arrive at? You are currently 34 seconds from the turn. At 30 mph you will, as you say, 44 feet per second. In 34- 7= 27 seconds you will have move 27(44)= 1188 feet and so will be 1500- 1188= 312 feet from the corner when you want to be notified.

    Looks right to me, but can anyone verify that is accurate?

    Any math experts that can validate this (Just like the old school questions)?
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    Re: How many seconds from my destination am I?

    The goal is to determine when I arrive at a defined number of seconds from the turn. So, if I want to know when I am 7 seconds from the turn and I am travelling at 30 mph, I need to know when I reach that point. So my plan is to compute the # of seconds until the turn every 1-3 seconds until I reach the 7 second mark.
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    MHF Contributor ebaines's Avatar
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    Re: How many seconds from my destination am I?

    Yes, your calculation is accurate. Whether it's "the best method" depends on how critical it is to be alerted at precisely 7 seconds out. Using your exxample, and assumimg steady speed, if you calculate every second then after 27 seconds yuo will be 312 feet away, which at 44 ft/sec = 7.09 seconds. So, do you signal an alert then, or do you wait another second, redo the calculation, and then signal an alert when you're only 6.09 seconds away? If it's critical to be as close to 7 seconds as possible you could alter the algorithm so that once the estimated time to the corner is less than 8 seconds you sound the alarm at the estimated interval. For example using the same numbers as above: when you calculate that the car is 7.09 seconds away you wait 0.09 seconds and then sound the alarm.
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    Re: How many seconds from my destination am I?

    Quote Originally Posted by ebaines View Post
    Yes, your calculation is accurate. Whether it's "the best method" depends on how critical it is to be alerted at precisely 7 seconds out. Using your exxample, and assumimg steady speed, if you calculate every second then after 27 seconds yuo will be 312 feet away, which at 44 ft/sec = 7.09 seconds. So, do you signal an alert then, or do you wait another second, redo the calculation, and then signal an alert when you're only 6.09 seconds away? If it's critical to be as close to 7 seconds as possible you could alter the algorithm so that once the estimated time to the corner is less than 8 seconds you sound the alarm at the estimated interval. For example using the same numbers as above: when you calculate that the car is 7.09 seconds away you wait 0.09 seconds and then sound the alarm.
    The only issue it may or may not be a steady speed. The vehicle could speed up or slow down. The location is known every second. That is why the computation (current speed and distance from the turn) and # of seconds from the turn will need to be known constantly and run every 1-3 seconds.

    If we receive GPS updates every second but only calculate every 3 seconds, then we will have +-3 second range and will have to make a decision on whether or not to notify.
    Last edited by holzert; February 22nd 2013 at 12:12 PM.
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  6. #6
    MHF Contributor ebaines's Avatar
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    Re: How many seconds from my destination am I?

    Quote Originally Posted by holzert View Post
    The only issue it may or may not be a steady speed. The vehicle could speed up or slow down. The location is known every second. That is why the computation (current speed and distance from the turn) and # of seconds from the turn will need to be known constantly and run every 1-3 seconds.

    If we receive GPS updates every second but only calculate every 3 seconds, then we will have +-3 second range and will have to make a decision on whether or not to notify.
    Your GPS data can give you speed as well as distance to the corner, correct? So every time you get new GPS data you redo the calculation of how much time is left befiore you sund the alarm using the latest speed and position data. If that time arrives before the next set of GPS data arrives then you sound the alarm.

    If you need better accuracy the only solution is to use a GPS that takes 5 or 10 measurements per second. FYI - I use such a GPS data logger for recording laps for high performance driving at the track - they're fairly inexpensive. But for normal everyday driving, it's probably not required, but again it depends on just how precise you need to be.
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    Re: How many seconds from my destination am I?

    Quote Originally Posted by ebaines View Post
    Your GPS data can give you speed as well as distance to the corner, correct? So every time you get new GPS data you redo the calculation of how much time is left befiore you sund the alarm using the latest speed and position data. If that time arrives before the next set of GPS data arrives then you sound the alarm.

    If you need better accuracy the only solution is to use a GPS that takes 5 or 10 measurements per second. FYI - I use such a GPS data logger for recording laps for high performance driving at the track - they're fairly inexpensive. But for normal everyday driving, it's probably not required, but again it depends on just how precise you need to be.
    Thank you. I think we are leaning towards voicing within a +-3 second range of the target "seconds until the turn." Then, if the driver comes upon a railroad crossing or traffic light (which will cause the seconds to stay static until it moves again), just display the seconds and not keep voicing "Turn right in 7 seconds, etc" Usually it is "Turn right in 200 feet" etc but some may prefer a time notice, not distance which would be based on speed but would be impacted by obstacles in the distance between. A conundrum...
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    MHF Contributor ebaines's Avatar
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    Re: How many seconds from my destination am I?

    This thread is turning from a math discusson into a product design discussion, but OK ....

    Given that the voice says "Turn right in 7 seconds," and that it takes about 1-1/2 seconds to say that, clearly it really doesn't matter whether the voice starts talking at 7 seconds versus 7-1/2 or 6-1/2, so don't worry about having the voice start at precisley 7 seconds.

    Another issue however is that when people make turns they slow down, so what you calculate as 7 seconds at 30 MPH may require, say, 10 seconds as the person slows to 15 MPH to make the turn. So the 7 seconds will never be accurate. Also - is that 7 seconds to the start of the turn? Or the mid point? It makes a big difference.

    Finally -if there's a traffic light that happens to be red at the intersection where you want to turn it's going to be a lot longer than 7 seconds before you can turn.
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    Re: How many seconds from my destination am I?

    Quote Originally Posted by ebaines View Post
    This thread is turning from a math discusson into a product design discussion, but OK ....

    Given that the voice says "Turn right in 7 seconds," and that it takes about 1-1/2 seconds to say that, clearly it really doesn't matter whether the voice starts talking at 7 seconds versus 7-1/2 or 6-1/2, so don't worry about having the voice start at precisley 7 seconds.

    Another issue however is that when people make turns they slow down, so what you calculate as 7 seconds at 30 MPH may require, say, 10 seconds as the person slows to 15 MPH to make the turn. So the 7 seconds will never be accurate. Also - is that 7 seconds to the start of the turn? Or the mid point? It makes a big difference.

    Finally -if there's a traffic light that happens to be red at the intersection where you want to turn it's going to be a lot longer than 7 seconds before you can turn.
    I apologize. That was not my intention, but the help and questions moved it into that arena. My initial goal was to verify my math for determining how many seconds at a given rate of speed it would take to get to a destination in feet. Everyone helped me to verify that, and I am grateful. The discussion also brought up variables that would have an impact on the result or change it in the process like railroad crossings and traffic lights, etc.
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