Exercise : Measuring heights of trees outside the forest (TOF) in digital orthophotos (DOP)
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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 is known 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 \(h_2=s_2*\tan \alpha\)