Determining Height

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Determining Height
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Introduction

• For many landscape jobs it is important to be
  able to determine the height of features in the
  landscape.
• Trees
• Buildings
• Etc.
• The best equipment and method to use is
  determined by the desired accuracy and precision
  of the data.
• The equipment and methods used can be divided
  into two categories
• Estimates
• Measurements.

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Estimate Methods

• Shadow
• Line of sight
• Felling
• Fixed angle

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Estimating HeightShadow Method

• The shadow length of all objects is proportional
  to their height.
• The height of an object can be determined by
  measuring the shadow length of an object with a
  known height and comparing it to the length of
  the shadow for the unknown height.

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HeightShadow Method-Example
Determine the height of the tree.
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HeightShadow Method

• Advantages
• No surveying equipment
• Easy math

• Disadvantages
• Requires sunny day
• Must have clear space to see shadows.
• Low precision

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HeightLine of Sight Method

• The line of sight method is base on the
  principles of right triangles.
• The ratio of the lengths of the sides of a right
  triangle are the same as long as the angle is the
  same.

If two lengths of a small triangle and one side
of the large triangle are known the length of the
other side of the large triangle can be
calculated using a ratio.
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HeightLine of Sight--cont.

• Select a stick of known height.
• Move away from tree some distance and place stick
  in ground.
• Insure it is plumb
• Lay on ground and sight across top of stick to
  the top of the object.
• Move towards or away from the stick until the
  sight line is aligned with the top of the stick
  and the top of the object.

• Measure the distance from the stick to your eye
  position.
• Measure the distance from your eye position to
  the base of the tree.

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HeightLine of Sight Method--Example

• Determine the height of the tower.

• The stake and sight position form one triangle,
  the tower and sight position form a second
  triangle.
• Both triangles have the same angle.
• Therefore

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HeightLine of Sight Method--cont.

• Advantages
• Low tech
• Doesnt require sunny day
• Adaptable to many different objects
• Easy math

• Disadvantages
• Difficulty establishing line of sight accurately.
• Low precision
• Precision is reduced if stake is not at same
  elevation as base of the object.

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HeightFelling Method

• The felling method estimates the height of an
  object by measuring the relative height with your
  hand and a pencil, or similar object, and then
  rotating the hand to lay out the same distance on
  the ground.
• The end of the pencil is marked on the ground and
  the distance is measured.
• Works best with a helper.

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HeightFelling Method-Example

• Determine the height of the house.

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HeightFelling Method-Example cont.

• Reproduce the height of the house with a pen or
  pencil.

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HeightFelling Method-Example cont.

• Rotate the pencil 90 degrees and align your thumb
  with the edge of the building.
• Stake the end of the pencil in line with the
  building.

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HeightFelling Method-Example cont.

• The distance from the house to the stake is the
  height of the house.

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HeightFixed Angle Method

• The fixed angle method uses a principle of
  triangles--the legs of a 45 degree triangle are
  the same length.
• Easy way to get a 45 angle is to fold a piece of
  paper.

• The height is determined by sighting along the
  hypotenuse of the triangle until the line of
  sight aligns with the top of the the object.
• The height of the object is the distance from the
  object plus the eye height.

The paper must held horizontal for acceptable
results.
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HeightFixed Angle Method-Example

• Determine the height of the tree.

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Measuring Methods

• Transit
• Others

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HeightMeasuring-Transit

• With a transit the vertical angle to the top of
  the object can be measured using the tangent trig
  function.
• Knowing the angle, the height of the instrument
  and the distance from the transit to the object,
  the height can be calculated.

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HeightMeasuring-Transit Example
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Questions