? for you math wizzards

Horse Plains Drifter

March 30, 2007 05:30

What is the proceedure for calculating the distance to an object when all I know is how high the object is? I want to calculate how far it is across my neighbor's field. There is a wood gate at the far side, so I can walk out and measure the height of the gate.

Thanks in advance for any help.

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  shoff14

  March 30, 2007 05:42

  You can use trig to find this type of problem. Besides the height of the object, you will also need an angle. In this case, the one from the ground to the top of the fence. You can find a rough estimate with your eyes, a protractor, string, and a weight. Tape the string onto a protractor with the weight making the string hang. Get on the ground, eye ball the fence down the protractor, look at your angle of the string. This will be the angle you will use in the calculations.
  
  If you know the height of the fence you can take the
  
  tan (theta) = opposite/adjacent
  
  so adjacent = opposite/tan (theta)
  
  theta = angle you find
  opposite = the height of the fence
  
  You could also us the inverse function, but really not any need to.

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  elkoholic

  March 30, 2007 05:47

  quote:Originally posted by MT357
  What is the proceedure for calculating the distance to an object when all I know is how high the object is? I want to calculate how far it is across my neighbor's field. There is a wood gate at the far side, so I can walk out and measure the height of the gate.
  
  Thanks in advance for any help.
  
  
  You will also need the angle measurement from the far end of the field to the top of the gate. It will be such a shallow angle so you will need some survey equipment or the at best you will have a SWAG. (scientiffic wild ass guess)

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  Tailgunner1954

  March 30, 2007 05:49

  The simple way is to count how many steps it is to the far side, and multiply by 3.
  
  Otherwise your going to need to be able to accuratly measure the angle between the top and bottom of the gate.
  Once you have the angle and height, than it's simply plugging in the numbers. Distance across field = height of gate x cotangent of the angle

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  Tailgunner1954

  March 30, 2007 06:00

  Another way, but not as accurate, is to use a 6" machinests scale (in 64th's) held at arms length to measure the "height" of the gate.
  Than measure the distance from your eye to the scale. From there (knowing the true height of the gate) it's a simple case of using "similar triangles" to solve for the distance EX: 1/4" (on scale) is to 4' (true height of gate) as 2' (distance to scale from eye) is to X (distance across field)

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  Cubslover

  March 30, 2007 06:24

  I'd have to dig out my Descriptive geometry textbooks.
  
  We used to solve problems like that. Except they took about 20min a peice.
  
  I'd say Tailgunner's last post would be the easiest, not the most accurate, but would give you an answer.
  
  Make sure that, if you were to draw a line between the gate and the object, then an invisible line from you to the center of the first line is perpendicular.

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