I'd like a tool to measure the height of the neighbours' houses etc by geometry or trigonometry or drawing triangles on paper, the sort of thing i see surveyors with on a tripod, but I dont know what it'd be called. (It's greek to me)
I dont need anything very accurate and expensive, so if anyone can tell me the name of what i want, or better provide a link to a cheap one, please do!
We made one in trig lessons at school. Good teaching method as it brought home the value of learning how to do apparently esoteric stuff like sines and cosines. ISTR it was something like a cardboard inner tube from a kitchen roll, gluing a cotton cross-hair over either end, then a protractor taped to the outside, and a plumbline hanging adjacent to the protractor - I'm sure you get the idea; you look down the tube and align both your crosshairs with next-doors' chimney pot, then have an assistant read off the angle indicated by the plumbline. You measure the ground distance between you and the neighbours' house wall, and a bit of trig gives you the height of the chimney. Very rough and ready
You stand some way back - use the measuring tape to let you know how far back you are, add of the height from the ground to your eyes, then use the clinometer to get the angle you need to look at to look at the height of their gutters.
The use the tangent function to work out the height.
h = tan(x) . d
where x is the angle and d is the distance from you to the base of the thing you're looking at the top of.
It won't be that accurate as the angle will change slightly with your height, so to make it more accurate, lie down.
You can make a clinometer with a protractor, bit of string, and some blu tak. Good picture of a home-made one here:
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if you don't have a scientific calculator or know what the tangent function is, just walk back from it until the clinometer reads 45 degrees, then the height is the same as your distance back.
If you use a level and a protractor to get yourself looking up at the building at precisely 45 degrees from the horizontal - move towards and away from it until it is 45 degrees, then measure your distance to that building - the height of the building is that figure, plus the height to your eyes. All of this assumes the ground is level between you and the building.
When I was in the Scouts many moons ago we were taught how to measure the height of trees and buildings using our trusty staves :-) Simply measure the distance (say 100ft) to the subject, eye on the ground, stave at 1 tenth of distance, mark off point on stave looking up at the subject. Then simple geometry to work out height of subject.
You can do it with a 1m rule (or any stick of known length) and some sunshine.
Wait for a sunny day, walk to the end of the shadow of the tallest part of the building and mark a point. Stand a ruler on that point and mark the end of the shadow cast by the ruler. Now measure the length of the rulers shadow and the buildings shadow. The ratio of shadow lengths will be the same as the ratio of ruler and building heights - and you know one of them! ;-)
george (dicegeorge) coughed up some electrons that declared:
It's totally over the top for your job I suspect unless you want millimeter accuracy, but years ago I hired a Leica TotalStation.
That's a theodolite that has a laser rangefinder built in, and a fancy computer, so once given a direction for north and set up to believe it's sitting on coordinates (0,0,0) for example, it will give 3d cartesian coordinates of anything you can point the laser at - in practice, a good
2-3 houses away, without resorting to placing reflectors on the targets.
I was actually helping my father sort out some measurements and I fancied the excuse to have a go and his (now my) house has some complicated slopes on the land.
Turns out, now that the data is proving quite useful.
Hire charge was around 100 quid for a bank holiday weekend as no professional would want it then. Only scary bit was being responsible for about 3000 quids worth of equipment without insurance! 2 weeks reading the manual in advance saved a lot of faffing. They're complicated to master the operational details, and yet powerfully simple to use when compared with the alternatives.
I'm sure Niels Bohr would have come up with that one, had the technology been around at the time (qv John Stumble's post, for anyone who doesn't know what the hell I'm on about).
Take a digital photo from a long way away. Measure something along the ground by the houses. Look at the photo with a program that shows the pixel position of any point. Compare the pixel heights with what you measured on the ground.
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