- We've looked at some data capture tools,
now let's go the other direction
and look at tools that can bring the information
we already have in a digital model
out to the field where we can use it to build.
The development of the robotic total station
has completely changed the way
that construction layout is done.
While it's still the surveyor's job
to locate things like property lines
and maybe building corners,
the construction team typically has to take it from there,
accurately locating every element of a structure
to be built and put in place.
Pairing the use of a robotic total station
with an up-to-date and accurate building information model
can allow the builders personnel
to quickly and accurately lay out everything on a site
from openings and sleeves in a floor
to wall openings and equipment locations.
A robotic total station takes its input
from the building information model,
so it knows where things are supposed to be located.
Once the operator calibrates the equipment's location,
in other words, tells that piece of equipment
precisely where in the building it's located,
it spins around, it projects a laser beam,
and that beam can be read by the receiving stick,
which is outfitted with a tablet.
The user simply walks around,
and the receiver will tell them
when they've precisely located something
like the corner of a floor opening.
Think about this.
You would no longer need a tape measure
to pull dimensions off of some existing column or edge form
to lay out your openings and sleeves.
You can just use the robotic total station
to walk the deck and locate them all much faster
and with a much higher degree of accuracy.
So why isn't everyone everywhere doing this?
Well, there are some limitations to be aware of.
First of all, this equipment is expensive.
There has to be enough on a project
to justify its use and expense.
Secondly, you do have to have an accurate model
to use as the input.
And then finally, you'd have to understand
how to deal with construction tolerances.
I think this is an important part of the discussion here
because when we talk about using lasers to scan and lay out,
and we discuss the really high degree of accuracy
that can be achieved,
it's important to remember that in construction,
we still have allowable tolerances for the things we built.
For example, concrete formwork
is permitted to have a certain tolerance.
Rebar that's designed to be installed at certain locations
is allowed to be installed at that location
plus or minus an allowable tolerance.
It's not reasonable to expect to eliminate these tolerances
when we build things in the field.
Some of these tools I'm discussing
will certainly help us reduce them.
And some methods of construction,
like offsite prefabrication of construction elements,
also greatly reduces variances.
But when you're combining things that might be perfect
or have a very low degree of variance,
with things that are going to have allowable tolerances,
you have to have a strategy to deal with it.
Let me give you an example
to help illustrate my thoughts here.
On the project example that I mentioned earlier,
the hospital patient tower,
the frame was structural steel
and the floors were concrete slabs
over corrugated metal decks.
Both of these elements were site-built
and they had allowable tolerances.
Now, being a hospital,
the slab had many slab openings and penetrations,
a lot of which needed to end up inside of a wall.
So using a total station,
they placed these openings in precisely the correct place
according to where the models said they were supposed
to be located out there in the real world.
However, the walls were not always constructed
with the same precision,
sometimes resulting in the sleeves coming up
outside of the actual wall.
In the real world of construction,
you need to recognize these things.
On this particular project,
after they used their total station to lay out the sleeves,
they used a laser scanner to scan the deck.
This single scan let them check for these as-built variances
by comparing the scan with the building information model
to get a complete picture of everything
before they place concrete.
This way adjustments could be made in the field
or the model could be updated,
whatever was more appropriate.
Now this is one strategy,
and it worked well for them and their specific needs.
Your needs might be different,
and the equipment you have available may be different.
Just keep this issue in mind, and be aware
that you need to think through the potential impact
and develop a strategy to deal with it.
You don't want to create more issues with technology
than you solve.