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How does land surveying work?


We use all kinds of measuring tools in our
everyday lives: rulers, protractors, squares, and tape measures, etc.. These work fine for small- and medium-sized
projects, but what if we need to layout something big like a road, bridge, dam, or pipeline? Hey I’m Grady and this is Practical Engineering. Today we’re talking about one of the civil
engineer’s most important companions, land surveyors, and we’re also going to try a
little bit of surveying you can do at home. This video is sponsored by Blue Apron, more
on that later. Surveying is essentially the science of taking
big measurements, and you’ve probably seen these guys on the side of the road looking
through fancy equipment on a tripod. Just about any civil engineering project starts
with a survey to determine the legal boundaries between parcels of property, the location
of existing infrastructure, and the topography and slopes of the land. Humans have always had a penchant for building
big stuff which means surveying is career full of history and tradition. Behind every wonder of the ancient world was
an ancient geometry nerd who laid out the angles and alignments during construction. Surveying is also how we created accurate
maps of the continents like the Great Trigonometrical Survey of India, which took almost 70 years
to complete. I personally think everyone should aspire
to accomplish something in your life that can be prefixed with the words “great trigonometrical.” The ubiquitous tool for a survey is called
a theodolite, and it’s one job is to measure the angles between two
points. Combine those angles with distances from a
chain or tape measure, and you can triangulate the location of any point using trigonometry. Modern theodolites, called total stations,
can not only measure angles, but distance as well, and they have on-board computers
to do the calculations and record the data for later use. When you see a surveyor peering through a
funny telescope, it’s probably a total station, and he or she is probably sighting a reflector
to record the location of a point. That’s just scratching the surface of sophistication
with modern surveying equipment. With GPS and unmanned aircraft, things can
get a lot more complicated. But I’ve got a few ways you can do your
own topographic survey with fairly basic and inexpensive tools. Maybe you’ve got a drainage issue on your
land, maybe you’re planning a landscaping project, or maybe you just want to exercise
your god-given right to take measurements of stuff and write those measurements down
on a clipboard. That’s my kind of recreational activity. My goal is to perform a leveling survey of
my front and back yard, which is just a way to get the relative topography for an area. I laid out a grid of points on a map of my
house and then transferred those points to real life using pin flags. Now I just need to pick my datum or base point
and measure the relative difference in height between that point and all the others. I tried a few ways to do this and there are
no sines, cosines, or tangents required. First, a sight level which is essentially
a combination of a telescope and a spirit level. To use it, first get a buddy or a willing
spouse to hold a surveying rod on the point of interest. Now, look through the sight at a surveying
rod and raise or lower the end until the bubble is centered on the line. Once it’s centered you know that you’re
looking at a point that is exactly level to your eyes. Simply subtract the height of your eyeline
with the height measured on the rod and that’s your elevation. It’s not a precision technique, but it is
cheap and simple which the most you can usually hope for in any part of a home improvement
project. The next way I tried is a water level which
is literally just a length of clear vinyl tubing filled with a liquid. As long as there are no bubbles or kinks in
the line, the free surface at each end of the tube will self-level. I kept one end at my datum a fixed height
and measure the height of the water at the other end as I carry it around to each of
my points. It’s a little more unwieldy but it does
have a distinct advantage, no line of sight required. You can use this method around corners or
behind trees with no problem, and again, it’s a cheap and simple solution. The third method to take a level survey worked
best for me: my laser level. Here’s the thing: I really like lasers. I relish any chance I get to use them in a
constructive way, and this is perfect. The laser level creates a perfect horizontal
line that can be used to line up cabinets or tile, but it is also easy read on a surveying
rod. You don’t need a helper, but you do probably
need to wait until dusk unless your laser is really bright, or you have these sweet
laser enhancement glasses. This isn’t the cheapest solution for a DIY
land survey, but it is the fastest one I tried, and it’s a tool a lot of people already
have. Surveying is one of the oldest careers in
the world, and also one of the most important. Why? Because land is important. If you own some, it’s probably your most
valuable asset, and even if you don’t, you’re pretty much stuck to it no matter where you
go. As a career, surveying is a fascinating mix
of legal knowledge, field work, and technical challenges. And since most civil structures are too big
for conventional measurement tools, the surveyor is one of the most important companions for
the civil engineer. Thank you for watching, and let me know what
you think! Thanks to Blue Apron for sponsoring this video. We are still in the process of getting settled
into the new house. After a long day installing lights in the
workshop or throwing away all the junk left by the previous owner, it has been really
nice not to worry about groceries. Blue Apron delivers all the fresh ingredients
you need, right to your doorstep, in exactly the right proportions to create delicious
recipes at home. If that sounds like something you’d be interested
in, the first hundred people that click the link in the description will get 3 meals free
with their first order. If you like it, you can continue your subscription,
and if you don’t, hey, you just got three free meals shipped right to your doorstep. Again, thanks for watching, and let me know
what you think!

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