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Measuring Distance - Parallax Assignment HELP

  1. Jun 15, 2006 #1
    :confused:

    Hi everyone.

    I have this assignment whereby I need to use the parallax method to calculate the distance to a pole from a base line on our school field. I am kind of confused as to how I can apply the parallax method to do this on our assessment day.

    We know that on one end of the rectangular field, there is a baseline market in 1 metre intervals while on the other side there is a line marked in 0.8 metre intervals. The pole is somewhere in the middle of the two and we need to know how to find the distance. However one condidiotn is that we can't use purely geomtrety but we actually need to apply the parallax method.

    After much researhing I have decided to look at the pole from either end of the baseline (whose distance I can emasure) and see how far the pole has moved relative to the line of the opposite side. I've got these two triangles now but the only problem is I have no idea how to emasure the angles that I need (parallax angles). We can't use an angletron or any other angle measuring machine, but we can use a protractor. The only thing is, I think the protractor won't give me very accurate measurments.

    I'm not asking for anyone to do the assignment for me lol... I jsut need ideas on how to measure the angles and whether or not you think my method is ok so far and any improvements that could be made.

    Any help would be very much appreciated.


    Thank!
     
  2. jcsd
  3. Jun 15, 2006 #2

    Andrew Mason

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    Perhaps you could start by explaining how you propose to use the parallax method to calculate the pole height. What distances and angles will you be measuring?

    AM
     
  4. Jun 15, 2006 #3

    We don't need to calulate the pole height. Just the distance from the baseline to the pole itself.

    I havent' worked out a formal method as yet (which is what I'm having problems with doing because of the parallax angle). But I know the following measurements (or I can work them out)... the length of the baseline and the parallax shift distance caused when i look at the pole from either end of the baseline relative to the opposite line. Form there (if i had the parallax angle) I could use the sine rule or something similar to calculate distance.

    I hope that made sense.
     
    Last edited: Jun 15, 2006
  5. Jun 16, 2006 #4

    Andrew Mason

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    I assumed that you wanted to calculate the pole height because calculating the baseline makes no sense. The baseline is marked off on the field so you can get the distance of the baseline easily. In order to do a parallax calculation, you have to know one length and two angles in the triangle. Are you given the pole height?

    Can you give us the question as it is worded?

    AM
     
  6. Jun 16, 2006 #5
    No unfortunately we are no given any other details apart from the lengths of each baseline and the distance from one baseline to the other. I was getting a bit confused as I thought you could use one of those distances to calculate the distance to the pole, but I went over my ideas and yes it does not work. :(

    The actual question is quite vague. It just says
    "Using the parallax method calculate the distance to a pole from a base line on the oval. You will only work from the abseline at the western end of the oval" You will only measure and caluclate the distance from the abseline without measuring it. No electronic devices may be used except a calulcator. You will need to develop a parallax method to determine the distance from the baseline to the pole and use this on the assessment day to determine the distance."

    Thanks again
     
  7. Jun 16, 2006 #6

    Andrew Mason

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    Ok. It helps to have the whole problem. You omitted to mention the oval track before!

    But I still don't understand the problem. It seems there is some information missing. Did they provide a diagram? If so, can you post it or describe it in detail? Is the baseline between two points on the oval? Do they give you the radius of the western end of the oval track?

    AM
     
  8. Jun 17, 2006 #7
    They provided a simple diagram:


    It is basically just a rectangle representing the field. The length of the rectangle is given as 91 metres. The left side of the rectangle (the western end) is our base line marked in 1 metre intervals. The right side of the rectangle (eastern end) is marked in 0.8 metre intervals. That is the only information we are provided with.


    The biggest problem worrying me is how to calculate the parallax angle. I can easily calculate the parallax shift by observing the pole and different ends of the base line but aprat from that I need the angle. We are also not allowed to use purely geomrety but we can use trigonometry..


    Thanks.
     
    Last edited: Jun 17, 2006
  9. Jun 17, 2006 #8
    By the way just to clarify some details. They call the playing field "the oval" but it is actually just a normal rectangular playing field.
     
  10. Jun 17, 2006 #9

    Andrew Mason

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    If I understand the problem correctly, you have a pole somewhere in the middle of a rectangular field that is 91 m. long and some distance less than 91 m. wide. You want to measure the perpendicular distance from the west edge of the rectangular field to the pole. You want to do this using parallax rather than direct measurement. This is the case even though the field is marked with lines parallel to the west edge at 1. m intervals up to the pole. The field is also marked with lines parallel to the east edge of the field at .8 m. intervals.

    Is that a correct description of the problem?

    AM
     
  11. Jun 18, 2006 #10
    Yes, that is all correct
     
  12. Jun 18, 2006 #11

    Andrew Mason

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    Since you can measure the length of the base line, presumably you can measure a portion of the base line. At each corner could you not measure the angle to the pole by marking the point where the line from the corner to the pole intersects the first hash mark (1 m line). That would give you a right triangle with sides 1 m and a measurable distance along the base line. Measure that distance and you can work out the angle.

    Or just use the protractor. You have to use some kind of measuring device to find the the angle.

    AM
     
    Last edited: Jun 18, 2006
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