MALE_1: Going to be talking to us
about terrestrial laser scanning.
Dr. Karen Gran: Thanks. Again,
thanks for inviting me
here to talk with you guys about this.
I use lighter now for many years,
starting with aerial lidar and then more recently
getting into terrestrial lidar.
I want to talk a little bit about
what the differences between
aerial lidar and terrestrial lidar and some of
the applications that are specific to terrestrial lidar.
Terrestrial laser scanning is a generic term or TLS.
It has a lot of different names it goes by.
I've seen tripod-mounted lidar, ground-based lidar,
side-scan lidar, which isn't totally accurate because
you can scan not just to
the side, but all over the place.
But essentially, it's the same technology
that you have in aerial lidar,
only instead of having the instrument mounted on
an airplane flying over and sensing the ground,
now it's mounted on a tripod.
This is our Faro Focus
3D terrestrial laser scanner that I brought,
and I scanned you all
as you were coming back into the room.
You may not have even noticed it.
This is the scanner here in Iceland.
One of my colleagues was there
scanning ground marines and
actually looking at marines of
different ages and how they degraded over time.
I just grabbed this example off
the web because I think it shows very nicely
some of the detail that you could expect to
find in a terrestrial lidar unit.
We're now working on a tripod on the ground.
We're still obtaining very
high resolution topographic data,
but we get a lot of other stuff.
You can see here where this hole is,
that's where the tripod was sitting.
This scanner, when it does a scan,
does a full 360 scan
all the way up to the top and all the way down,
and the only thing that's missing
is basically the footprint of the tripod.
You can see the trees show up very nicely.
People who work in forest trees
and are trying to do tree surveys like
this because they can do scans and
actually get all the diameters
of all the trees that are around.
You see that the fence shows up.
You can actually get a point cloud that has individual,
very small scale features.
You also might notice that the density of
the points where that tripod footprint is
are very high and it
rapidly deteriorates as you go further away.
There is a very concrete range
over which your scanner can see.
Once you get beyond that range,
the signal really starts to deteriorate quite a bit.
But there's a way to get around that
because you could actually move the scanner
over to an area that has
a lower point density and take another scan.
That's one of the differences
between the terrestrial units and
the aerial units is that if I wanted to scan this room,
I would actually scan here and I
probably move it over there and maybe move it over there,
and then I'd stitch them all together.
You have to be very careful about
your control points that
you set out in order to stitch your scans together later.
The other things you might notice are the holes
or the shadows behind objects.
What you see is what you get.
If you're standing in one place and you see,
if I was to scan from here, I see a camera.
I'm going to scan the camera. I'm not
going to scan what's right behind it.
There's going to be a data hole
or a shadow right behind it.
But it's very powerful
particularly when you combine it with a campaign
where you're actually moving the scanner around to get
full 360 coverage of
the objects that you're interested in.
There are two main kinds of ground-based lidar.
There's time of flight versus phase shift,
and this is something that's a little
bit different than the aerial lidar.
From what I understand, most of
the aerial lidar data would be time of flight.
You're sending out a pulse and the pulse is
emitted and then you're getting back a series of signals.
We talked about the first return
where the canopy is sending out a signal,
and then the last return would have been
that bare earth surface that comes back.
There are terrestrial lidar units
that use time of flight technology.
There's also phase shift technology.
This is a phase shift lidar unit here.
Here you're sending out the lasers
at a particular frequency or at multi-frequencies,
and the shift in
that frequency is what you're
using to determine the distance
that you can use to get the time
of flight that you can use to
actually figure out how far things are away from you.
That's a subtle difference in
terms of the physics of how the data are collected.
Practically, it has some pretty important ramifications
for how you choose which unit you would want to use.
The time of flight units have a much farther range.
I've used time of flight units that have
a range of up to two kilometers.
From this tripod, it could see two kilometers away,
but they're notoriously poor up close.
If I wanted to scan this room,
a time of flight lidar unit would not
be the best application.
The phase shift lidar,
on the other hand, are really good at close range.
This one has a stated range all the way up to 0.6 meters,
but it doesn't do very well further out.
It's official range is 120 meters.
We don't usually try to use it
past about 100 meters away.
They're very close range.
They have very different applications.
A couple other practical features.
This guy officially weighs 11 pounds.
The time of flight unit here that's shown,
the one that I used in the field, weighed 80 pounds.
That has very practical implications
for how hard it is to move around in the field,
and the time of flight ones are significantly slower.
They're usually on the order of 10,000,
maybe up to 100,000 points per second,
and this can do millions of points per second.
We did actually do a full 360 at
a really low resolution scan in under a minute.
That makes it very practical to actually
do those multiple scans in the small area.
Having said this, technology
changes every day, as you all know,
and we're now to the point
where there's an overlap between
the close range time of
flight scanners and the longer
range phase shift scanners.
Actually got an ad from Faro yesterday saying,
hey, do you want to upgrade your scanner?
We have one now that goes up to 300 meters.
Some of the time of flight ones
are now getting closer and closer in range.
This is just an example from
a study done by Alonso et al.
which they actually took two of
these different technology scanners
that had similar range and
tried scanning the inside of a cathedral,
and they were looking specifically at differences.
Here, the color coding is just the difference
between the two different scan techniques.
They found that actually they're pretty close.
There were a few systematic things that were different.
What I thought I would do here is talk
about the workflow associated
with using the two different scanners.
You get an idea what a campaign is like using
a time of flight instrument for a large area
versus using a phase shift lidar unit from
a very close area using
a couple examples of work that I've done,
and then also talk about
some potential applications that are
more applicable to archaeology.
I'm a geomorphologist, so I spent a lot of
time just surveying the surface of the Earth,
but things that are sitting in front of the surface,
the Earth you might be interested in as well.
Here's an example of a time of
flight instrument that we use.
This is a Riegl Z620.
We took it out to Mount Pinatubo in the Philippines.
Those of you who may remember
pretty sunsets in the early '90s,
Pinatubo erupted in 1991,
and I've been spending probably the past 15 years or so
tracking channel evolution from that one.
This is just a Google Earth image.
Pinatubo is up at the top,
and then down at the bottom where that river
opens up and it gets all wide and gray,
that's the top of the alluvial fan.
We've been tracking sediment movement
and then deposition on the alluvial fan,
and we could do this pretty readily from
just simple cross-sectional surveys
when it was a grading at three or five meters per year.
Slow down a little bit since then.
I wanted to do is take this TLS system out
there and see if we can scan in the upper alluvial fan.
Then this is something we could
come back to 10 years later and
actually document the volume of
material that's been deposited there.
I also wanted to actually use this thing
to track lateral channel
movement more or less in real time.
The channels move around really fast.
They shift around very quickly,
so I wanted to see if I could scan it
and then scan it again two hours later
and actually track the channels moving and
the volume of material that was associated with that,
which is why we chose to use
the terrestrial laser system
instead of the aerial lidar system.
There is also people get a little touchy
about flying aerial lidar in other countries.
That was not a possibility.
This one weighs 80 pounds,
takes two people to put it up on top of the tripod.
You can imagine how fun that is on top of the truck.
We had it mounted up there to try
and get a better look angle.
We were for various reasons not able
to scale cliffs nearby to actually set this up.
The way that this worked is we set up
about 12 control points around the upper alluvial fan.
This is what a control point looks like.
In this case, we dug a hole,
we pounded in rebar, we put in some PVC,
we poured cemented, and we mounted
a pin on top of that that we could attach prisms to.
The control points had a prism,
and then we would actually use an RTK GPS
for each of those control points.
These are locked into real space.
We made these quasi permanent structures because
it would take about four to five days
to do that entire alluvial fan.
It's about two kilometers long,
about 500 meters wide.
Typically you would go and
you would set up your instrument,
you'd send somebody off to go and turn
all the prisms so they pointed at the lidar unit.
I walked a lot. Go walk
a kilometer and turn that prism towards me.
The unit that we were using
was one that was provided by UNAVCO,
which is a National Science Foundation funded lab.
They do a lot of the GPS work out in
the western part of the US and elsewhere.
I suppose they do GPS work all over the place.
But they also have some terrestrial laser scanners.
It's worth knowing about it.
If you're the PI on an NSF grant,
this is one of those potential opportunities.
They would provide the hardware and
the technician support for that.
They came out with us and they
were in charge of the scanning.
I moved a lot of prisms.
You move the prisms, then you sit down
at the computer and you have to find all the prisms,
you have to do a high resolution scan,
you've got find the next one, do
a high resolution scan, find the next one.
Then you hit go and you wait
about two or three hours while
the thing does a 360 degrees scan.
Very time consuming and if anyone bumps the truck,
or if it starts to rain,
there's a whole number of reasons
why that workflow gets
broken, we got to start over again.
It took us a long time,
probably about a week to do that alluvial fan.
We did it twice while we were there,
and then we also tried doing
the real time measuring lateral movement.
I'm standing here and my left hand is where
the bank was when we put that control point in.
Things move pretty quickly.
You had some field issues.
But that was the general workflow
of how you set this up and how you set up
your campaign to control points
in places that are visible from
a lot of places and
also that don't walk away while you're out there.
This is very different
than a typical campaign with this little guy here.
We've been using the phase shift lidar unit
to scan a bunch of
eroding bluffs around the Duluth area
as well as down in the Minnesota River Valley.
This is an example of this is a typical Duluth bluff.
It's the red lake superior clay.
This probably was collected with
just two scans and probably took less than an hour.
We would actually pound rebar in because we
wanted control points that we could come
back to over and over again.
We want to do repeat scans.
Getting at what Josh was talking about earlier,
we want to be able to detect change.
We put in our rebar,
we mount these guys.
These are what we used for control points.
We have a sphere.
You put your spheres out and sprinkle
them around the room or sprinkle them around the bluff.
You can actually see there's some green writing
there. These are the actual data.
These are colorized point cloud data
that you're looking at right here.
We would put those out. We'd do a scan.
I'd take about 10 minutes. We'd march
the tripod over someone else.
We'd do another scan, 10 minutes,
boom, we're ready to go.
Then you go back in the lab, you stitch them together.
The software can actually automatically find these
and stitch all the different things
together automatically.
It's really pretty slick.
These are the data that we were getting.
This is a little awkward, but you're looking
downstream at the bluff surface
itself at different points in time.
Then we can take those surfaces.
We can actually turn them into essentially DEMs,
only pointed at the bluff
and then do change detection between them.
This was the whole goal, was to
actually do geomorphic change detection.
We used RGIS plugin,
known as the GCD plugin that was
put together by Joe Wheaton out at Utah State.
It's free and available to anyone who wants it.
You create a DEM from your point cloud data.
You take the new DEM, the old DEM,
and you get a DEM of difference, a DoD.
The DoD shows you where all the changes have occurred.
In this case, the red is showing erosion,
blue is showing deposition.
You can actually map
volumetrically where the changes are.
You can also put in a variable uncertainty maps.
It's better than just saying this minus this,
because it actually lets you look
at the level of detection and
adjust that for the different
surfaces that you're looking at.
This is an example of some of
the DoD data from our bluffs.
Up at the top, that's the change in the bluff surface
from November in 2011 to April in 2012.
The picture on the right just shows what happened.
There was a slump that happened.
The top of that darker red is the top of the slump,
and it eroded down, piled up at the bottom,
and that's why there's that blue stripe at the bottom.
Then we had a pretty decent size flood that hit in May,
and the scarp actually retreated
further up and the whole thing slid down,
but we didn't have much erosion.
It actually was inflationary.
We ended up with what looks like a lot of deposition.
Then we hit that flood that Joe had talked about,
and this is just an example of
some of the changes that occurred in the river there.
There's my graduate student precariously perched on
a boulder in the middle of the river
that is now on part of the point bar.
This particular bluff 4-5 meters back in the flood.
We like to refer to that as the apocalypse.
This post just flooded.
June 20 and 21st,
there's a 500 year flood event.
It's a pretty big deal for anyone who is from Duluth.
This data here with the bright red,
that's the data from the flood.
We actually went back out and scanned it after the flood.
It's pegged at 2.5 meters of change.
There's a huge amount of
scour that occurred during that flood.
Then afterwards,
not a whole lot changed between June and November.
November is when they went and
flew the repeat aerial lidar.
Between the time of the flood
and the repeat aerial lidar,
not a whole lot was happening.
This is a way that we can actually
quantify how much change,
start linking it to the actual
hydrologic event that occurred,
and we did this on a whole bunch of bluffs.
We have a measure of how much erosion occurred during
the flood and how much erosion
occurred during essentially the rest of the year.
This is a very different scale application,
but we actually use this in our lab as well.
It has a range, it goes down to 0.6 meters.
We use it in this thing called the topo dome.
The round been there,
if you were to look inside of that,
you would see a little miniature mountain range.
Above it is a rainfall simulator.
Along the right hand side there is a slot,
and it essentially acts as the river mouth.
We can drop base level on the river mouth and
that base level fall will propagate up
into the landscape and gets
beautiful mountain range developing.
Down at the downstream end,
we can build out the delta.
We want to do is see how much change is occurring,
and then we can change the rainfall rate,
we can change base level fall.
We can do all stuff to
manipulate the system, and then we can scan it.
We have the scanner mounted upside down over this.
We slide it in, we scan it, we get a DEM,
we do it again later, and we can subtract them
and get a DoD. This is great.
This was set up as a class project initially that
students can go in and they can change rainfall,
they can change tectonics and
they can see the response in the system.
That's some examples of what we have done with this.
I thought I put out
a few potential applications
of what people who are maybe a
little bit closer to cultural preservation
and archaeology are using this technology for.
This is an example from Brian Brashaw
who's at UMD's Natural Resources Research Institute,
and he uses this scanner
for historic documentation of bridges.
He's actually scanning the bridges of Madison County.
One of the reasons that you're doing that
is to document them,
but also to actually put together as-built documentation.
They take the 3D point cloud data,
they pull it into CAD,
and they're able to produce
essentially blueprints for these bridges,
and they're scanning them inside and out.
Then it stitches it together and you have
these beautiful documentation. That's one example.
People are also using it to
scan iconic figures like
the Terracotta Warriors in
China or the moai in Easter Island.
These have been scanned with TLS systems.
Thus, you're documenting things that are
at risk of being destroyed.
You couple this to a 3D printer,
you can do all amazing things.
But also people are doing
statistical analyses on these things.
The Terracotta Warriors, I admit
I saw this on TV. I thought it was so cool.
They're scanning them and comparing
features like the ears to see if
they're all individual warriors or if they're repeats.
They have the 3D data so
they can actually make these measurements on it.
These are a couple examples.
Another one from Easter Island
just from the same paper where
they were actually using this
site documentation in the field,
and it sounds like this is what Dave was talking about.
They're actually scanning the dams
out in the river with the scanner.
Here they're actually scanning
some features in the field.
This is a well that one of
my former graduate students
Stephanie Day has been working on in American Samoa,
and very quickly, I'll
actually show you what these data look like.
This is a well in American Samoa that was collected.
It's very dark, but there's a well in the middle there.
It looks great on my screen.
You can see the trees were
scanned, so they're showing up.
You can see at a few places
those gray patches, those are data holes.
One of the nice things about this is the amount
of measurements that you would have to
do without a scanner to get
this detail would take a lot longer.
In probably two or three hours,
they were probably able to do enough scans
to get all of this detail.
But this is dark. We will move on.
They're also scanning ditches
and using that to actually make measurements on
the ditches and attempt to calculate
paleohydrology from this and try to
answer some questions as to whether
these ditches were used for irrigation or
whether they were used for flood control
or whether the size of them was really
more of a status symbol and had
nothing to do with the amount
of water they needed to move.
These are some examples of work that's
going on using actually the same scanner here.
There are some challenges with TLS.
With the aerial lidar, the data files are
massive and you need to be able to put all of
the files from a campaign together to stitch it all
together before you can
decimate it and process it at a lower resolution.
Processing time, it takes a lot longer to
process the data than it takes to collect
the data. We'll just leave it at that.
Generally use a proprietary software
for the initial processing.
Whatever system you're using,
you got to learn another package
of software to analyze that data,
and then you can put it into
something else that's more universal.
You do need to know what kind of lidar unit you need,
whether it's time of flight or phase shift and pick
appropriately. They're not cheap.
The one that we used in the Philippines was probably on
the order of $250,000.
This one's an order of magnitude less.
With time, the price comes down as well.
Then there's limitations to data collection.
What you see is what you get.
You see vegetation, you're going to scan vegetation.
It's a lot harder to get that
bare earth surface beneath it.
You get data holes and data shadows but you have to
be smart about how you're moving
your system around and getting those shadows filled.
Unless you have a lidar system that
has the green wave length, you can't see through water.
Water just comes out with no data.
Those are a few issues with it.
I'm going to throw up one last slide
which is not about TLS and then we're
actually going to turn this onto a
scan because this is cool,
and I see that this is where
the next phase of getting
the same style data is
something called structure from motion.
Write it down and Google it.
People are able to now get 3D
point clouds not from a scanner,
but from a whole bunch of photos.
You could take in this case,
244 photos they took of
this church and you can stitch them
together automatically and develop
a colorized 3D point cloud from that.
It's pretty impressive. These are just a few of
the software packages that are out there that
are relatively low cost to free.
I throw this out there.
If you think that
this application is something that you would love to use,
but maybe actually getting
the scanner to your site wouldn't work,
take lots of pictures and
investigate this too because I
think this is really pretty cool.
With that, I thought we would actually
go take a look at some scanned data and
then we'll actually do a scan.
This is an example of some data
from a bluff on the Knife River.
This is where the tripod would have sat.
Gosh, it's really dark out there.
Here are the trees up at the top.
The bluff is along and here.
There's the other side of the river.
Again, these are elevation data,
but this thing has a camera built in,
so you can also get color.
You can colorize your pixels
and look at it in real color too.
This is an example.
The density here is set more by the system that we're
actually using to visualize
this than the density of the point cloud.
The scanner itself. This is
a remarkably user friendly scanner.
I'm actually hooked up to it right now.
You can go in and change
parameters here so you can set your resolution.
Let's say the highest resolution possible and
the highest quality it's
going to take me two hours to scan.
This is going to be my scan size.
This is going to be the number of megapixels.
I could also reduce
the resolution and you'll see the time comes way
down to the point where I could
potentially scan this entire room in 47 seconds.
Other parameters that you can set,
you can turn the camera on and off.
If you're scanning with color,
what it'll do is do a full scan
and then it'll take photos as well.
What I'm going to do is set it to do
a really fast scan and then take the photos.
I'm going to start this going,
smile for the camera,
and I'll take questions
maybe while this is actually scanning.
We're going to start the scan.
That's just going to sit there and while
that's blinking itself away,
does anyone have questions about TLS in general?
Don't get paranoid. It's okay.
[LAUGHTER] Yeah.
MALE_2: You were very
interested in the Minnesota River Valley.
Are you still looking at Glacial River Warren
terraces and mapping [inaudible]?
Dr. Karen Gran: We had been scanning
a bunch of bluffs down in there
as part of a sediment budget in the luxor,
and we have been scanning some of those bluffs,
continuing to do the scans in part because like I said,
the time is in the processing of the data,
rather, the collecting of
the data doesn't take nearly as much time.
We're trying to just keep the data collection going.
They haven't been all processed yet.
We are doing a lot of work actually on some terraces,
trying to date the terraces and trying to look at
incision of the valley through time there as well.
A lot of that is with the aerial lidar. Other questions?
MALE_3: In the class project
where you do irrigation experiment,
what's the density of the data?
Dr. Karen Gran: The one where we actually have this
hanging right over the experiment,
we took that at two millimeter horizontal resolution.
MALE_3: How many points did we get for it?
Dr. Karen Gran: Well, that was about a meter wide.
Well, one meter times two millimeters, there we go.
About 200 points across them?
No. Did that right?
Five hundred points across point every two millimeters.
We actually collected that data at
a fairly low resolution
because we wanted the scans to go quickly.
A five minute scan would get
us resolutions high enough to get two millimeters.
MALE_3: But you can lower it down to [OVERLAPPING].
Dr. Karen Gran: If we had cranked it
up and taken 10 minutes,
we probably would have had one millimeter data.
We could even go finer than that if we really wanted to.
MALE_3: Is there a [inaudible]?
Dr. Karen Gran: Yeah. The scan that we just
hit in here in 47 seconds and now it's taking pictures.
Smile. That scan is going to give
us the back wall probably every 10 centimeters or so.
It's still pretty high resolution data,
but very low compared to what it's capable of.
All of that comes down to
how much time do you want to spend out there.
How fine do you want to go,
because we can do sub millimeter
with this pretty easily up close.
MALE_4: When you're doing a higher resolution,
is it doing multiple passes or
is it spending more time? I'm thinking about movement.
Dr. Karen Gran: It's turning really slowly.
You might have noticed it turned really quickly
when it was actually collecting the data.
It buzzed around in 47 seconds.
It would do that over the course of two hours.
It moves very slowly.
The other thing it can do is I set
it to sample like four times or something like that.
You can have an average a certain number of points.
You can have it average one or up to eight.
That's the other place where the resolution kicks in.
MALE_4: It's not picking up movement [inaudible]?
Dr. Karen Gran: It's not, but what's fun
is if it's scanned and you were moving,
then you get pinched.
Or if it scans while you're sitting
there and then you move over there and it
takes the photos because it does the photos at the end,
then your body shows up here,
but your picture shows up flat on a wall over there.
It's fun. [LAUGHTER] Generally
we're taking these scans and there are
always these 360 scans.
You can also window it in if
you just are focused on a smaller area.
You can do a 360, zoom
in and do that at a higher resolution.
But oftentimes you're in the scan,
but it's not an area you care about,
and so you're not really worried about it.
MALE_5: [inaudible]. Is that
purely a reflection of the bottom of the unit or
the scan do not, you know what I'm saying?
Dr. Karen Gran: It's the fact that
there's this right here.
Literally is just basically where the tripod is.
When I use it in the experiment,
we flip it upside down, and
so then the hole is up above us.
MALE_5: [inaudible].
Dr. Karen Gran: Well, if I was hanging from
up there but facing like this,
you'd still have the same data hole
would spread out underneath you.
But if I really wanted to scan this patch of floor,
I'd just pick this up and move it over there and
do another scan or I'd hang it off the ceiling.
Here's what we just collected.
This, like I said, was a really low resolution.
You can see, I got chopped.
I moved. But there you guys are sitting out there.
It's got all the way up to the ceiling.
This is the fish eye approach.
I don't know. This is
an example of a scan that one
of my students took of a flume,
she's got a braided river and a flume.
Here, she's actually able
to get individual channels, etc.
I'm going to show you
very high resolution on the scanner itself.
But that gives you an idea of how it's really very
easy and pretty straightforward
to actually collect the data.
I'm going to leave this setup.
I'll probably move it off in a corner.
But if people want to see it during the reception,
feel free to grab me.