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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.

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Again, thanks for watching, and let me know what you think!