Exercise : Measuring heights of trees outside the forest (TOF) in digital orthophotos (DOP)
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[[Image:shadow_length.png|450px|thumb|right|'''Figure A''': Shadow length ''s'' and object height ''h'']] | [[Image:shadow_length.png|450px|thumb|right|'''Figure A''': Shadow length ''s'' and object height ''h'']] | ||
| − | A simple application of the intercept theorem in elementary geometry is to determine the height of a tree by measuring the shadow length. According to Fig. '''A''' the shadow length <math>s_1</math> and the height <math>h_1</math> of a man made object such as an overhead line tower were measured on the ground. If the lenght of a tree's shadow is | + | A simple application of the intercept theorem in elementary geometry is to determine the height of a tree by measuring the shadow length. According to Fig. '''A''' the shadow length <math>s_1</math> and the height <math>h_1</math> of a man made object such as an overhead line tower were measured on the ground. If the lenght of a tree's shadow <math>h_2</math> is determined at the same time of the day we are able to compute <math>h_2=s_2*\frac{h_1}{s_1}</math> |
We may also use trigonometry if we know the sun elevation <math>\alpha</math>. The height of a tree is then computed <math>h_2=s_2*\tan \alpha</math> | We may also use trigonometry if we know the sun elevation <math>\alpha</math>. The height of a tree is then computed <math>h_2=s_2*\tan \alpha</math> | ||
Revision as of 14:55, 15 July 2014
Contents |
Shadows in orthorectified remote sensing images
A simple application of the intercept theorem in elementary geometry is to determine the height of a tree by measuring the shadow length. According to Fig. A the shadow length \(s_1\) and the height \(h_1\) of a man made object such as an overhead line tower were measured on the ground. If the lenght of a tree's shadow \(h_2\) is determined at the same time of the day we are able to compute \(h_2=s_2*\frac{h_1}{s_1}\)
We may also use trigonometry if we know the sun elevation \(\alpha\). The height of a tree is then computed \(h_2=s_2*\tan \alpha\)
