EQUIPMENT:
Suunto Clinometer
http://www.cspoutdoors.com/clinometers.html
Leica Disto A3
http://www.leica-geosystems.com/cpd/.../lgs_29794.htm
INITIAL SETUP AND CALCULATIONS:
There are really two ways to measure building height with these devices. The method I use is simple and works best in a flat city like Phoenix (you have to make additional adjustments if you are trying to do this on a slope):
1. Position yourself near a tower (be sure to select a location far enough away that you can see the top and the base clearly--I also center myself on a flat side of the target) and measure your distance horizontally to the base of the tower using the Leica device. You must be level when you do this. This will give you a distance we will call y. For example, let's say y = 120 feet. The precise location of the building's entrance doesn't matter in Phoenix because all skyscrapers here are built on perfectly level ground, so the base all the way around the building is the same as the front entrance. In a hilly city like Seattle, you would have to make other adjustments.
2. Using the inclinometer, sight the top of the building (I do this process twice if there is a tip versus roof height) and read the angle percentage (I believe this is a tan figure) from the device. Convert this to a decimal (divide by 100). We will call this x. For example, let's say x = .42. This works best if the building's max height is at the perimeter - i.e. a flat-topped building, and the sides are at a 90 degree angle to the ground. If you are measuring the tip in a center of a high-rise (steeple or crown), you will need to determine the building's width and add half of that figure to your distance. If the building's sides are not at a right angle with the ground (i.e. pyramid-shaped structure), you will need to determine the slope and correct your distance figure - or you could lay on the ground to do this.
3. Multiply x and y, then add your height to this number. This yields the actual height of the building. So, for our example, .42 x 120 = 50.4. My eyes are about 5.7 feet above the ground, so the actual building height is 56.1 feet.
The other way is to figure out the ratio of your shadow to your height and then determine the length of the building's shadow, then multiply that last figure with the ratio you determined previously. In a bright, sunny city like Phoenix, determining the precise location of the highest point (longest shadow) is easy. The only drawback is if that point happens to be in the middle of a street, then you either risk life and limb to secure the measurements or come back at another time.
EFFICACY:
These methods are 99% accurate if done right, and I've measured several buildings with expected results. I calculated the height of Chase Tower (Phoenix's tallest) at 481.2 feet and the actual height is 483 or 486 feet, depending on what source you believe. Obviously, shorter buildings yield more accurate numbers.
This works the same with meters and feet.
--don