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Height by shadow length.


Berlin tv towerSometimes, 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 the 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 the 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.shadow Berlin tv towerThe data from the image was entered into the online calculator by default and calculation of the tower height is 367 meters. It's slightly different from reality, therefore the calculation has a small error.

on-line calculator Height by shadow length

Calculator of the object height by measuring its shadow length in the Google Earth

ENTER DATA:
day: month: year:

latitude ° 
longitude ° 
Timezone ±GMT:

Shadow length:
Shadow azimuth: ° 

Calculate
RESULT:
Clear all

±GMT – Time different from Greenwich (UTC)

To correctly determine the azimuth of the shadows, we need to measure its length from the end of the shade towards the object. The method of determining the 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.)

Other calculators:

 

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