Sometimes, when designing antennas, the radio-hobbyist needs to find the height of some object, such as Telegraph pole, tall chimney, etc. The height of such object can be found using the theorem on similarity of triangles and by direct measurements on the ground. However, if you use Google Earth, you can determine the height of a high object without leaving your computer. This idea belongs to UA6IGI.
Using Google Earth we can measure the length and azimuth of the shadow from the object with a ruler on the program toolbar. In addition, we need to know accurate geographic coordinates of the object and the date of satellite image. This information is located in the bottom of the window. Using these data we can calculate the altitude of the sun above the horizon at the time of the shooting and find the height of the object. For example here's an image of the Google Earth window with the measurements of the shadow from the Berlin TV tower. The data from image was entered in the online calculator by default and calculation of the tower height is 367 meters. It's slightly different from reality, therefore the calculation have a small error.
Calculator of the object height by measuring its shadow length in the Google Earth
To correctly determine the azimuth of the shadows, we need to measure its length from the end of the shade towards the object. Method of determining height of an object by measuring its shadow length in Google Earth has the following limitations that reduce its accuracy:
The error of measuring the length of shadows.
The slope of the surface (non-horizontal) on which the shadow falls
The end of shadow drops on object having the own height (garage, adjacent building, etc.)
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