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Question 1

Gps accuracy:

Answer 1

dilution of precision:
1/volume of tetrahedron
-4 satellite smallest volume 1.6 almost never get it

Question 2

Crossprocessing

Answer 2

data collected but not corrected

Question 3

At 4sigma (standing)

Answer 3

(5) Autonomous - bad 15m
(4) WAAS - 3m
(1) PP GPS less 1cm
(2b) RTK GPS- 1-2cm
(3) NRTK GPS - 2-4 cm
(2a) Opus static
(2c) Opus Rapid Statics

Question 4

variance in matrix

Answer 4

diagonal of matrix , variance of xyz normalized, always less than 1

Question 5

time delusion of precision

Answer 5

time error from clock bias

Question 6

high confidence in position

Answer 6

have small number

if degraded values pick another time of day or not use gps

Question 7

differential gps

Answer 7

ome place we know the location precisely, set unit there too and get know errors and subtract the know position from computed and have delta xyz to represent error

can be done after taking the measurements called cross precessing or real time processing called real time kinematic processing have broadcast from the station that is sitting on know coordinates to the one that is moving around
known station unit called base the other one rover
we are factoring out the big source of error which is atmosphere, clock bias, position of orbits

Question 8

WAAS

Answer 8

alk about true form of differential gps

12-16 meter 95 % confidence for regular gps

WAAS (wide area augmentation system) developed TO land automatically plane where 95% confidence limit was 3 meter instead of 12

Question 9

Station calculation correction facto

Answer 9

here is a central station in west cost and another one in the east coast that communicate with satellite
2 satellite for WAAS one signal west other east coast they are geosincronize, always at the same location in the sky (rotation of earth same as angular rotation of satellite, 23000km elevation above us)
GPS unit set up on top the station in known benchmarks calculate error and broadcasting to satellite , gps unit receives on the main L1 frequency the WAAS signal

cannot survey off this because cannot have that kind of error on foundation of a building

Question 10

geocentrical orbits

Answer 10

satellite always overhead so angular velocity of earth same as angular velocity of satellite =, moves with earth
Radius dependent, circle earth twice a day

expectation data should be better with WAAS on

Selective availability, degraded signal associsated with gps that is now turn off

Question 11

Network RTK

Answer 11

broadcast to the service, looks for closest stations and calculate the error the these stations and apply them to you position

What kind of improvement do we get from this?
error reduced to millimeters
gets extremely precise measurement

Question 12

Opus

Answer 12

e have nova and national geonetic surface of US government set standard for Us and global with collaboration with european unit and japan, set global reference frame for all measurement and update annually
They set up station call Continuous Online Reference Stations (CORS) gps sit units set up permanently, location known to mm, your errors are calculated from this references

OPUS is post processing, they provide the base, errors in cm

problem with height factors out

Question 13

how does opus compute position

Answer 13

Calculate baseline solution between your position and cors station around you and averages those eros and applies them to your value
need L1 l2 receives, need to collect at least 2 hours of data

Question 14

Antenna height

Answer 14

supply height of antenna over you bench mark to the reference mark on the antenna

all position get subtracted off give position of benchmark and post processing will take out atmosphere effect and bring us as close as possible to the bench mark value

Question 15

Negative geoid height

Answer 15

means that he geoid is below ellipsoid

Question 16

scale factor

Answer 16

mount of distortion you will expect on a map depending on how much the surface of the earth extended about the flat plane of the map

Question 17

tip to tip valu

Answer 17

latitude/longitude/height value the maximum value of all the data
from hundred of measurement the full range normaly distributed at 4 sigma 95% confidence

Question 18

Antenna - TPSHGDE

Answer 18

russian and US satellite

Question 19

Opus good data?

Answer 19

Ephemerous - orbit parameter for satellite, broadcast values 5m of error, 12 hour later ultra rapid solution to try to improve on location of orbits of satellites

Check antenna chosen and height are correct
Peak to peak error less than 5 cm
Which operating station were used

24 hours rapid orbits improve precision location of satellite
2 weeks after,ngs post precise orbits

Opus answer improve with time

Question 20

how good are orthometric height in opus?

Answer 20

Add error geoid / confidence limit
errir eklipsoid + 5 cm for geoid

ex 4sigma 95% confidence
8cm
Measurement of orthometric height has an added error associated to adjustment

Question 21

OPUS accurancy is

Answer 21

time dependent
how things improve with time
how long you left gps in one location

longer you keep gps making recording the better the measurement gets

Question 22

Opus rapid static

Answer 22

session less than 2 hour more than 15 min
baseline more than 3 station
static only 3 station and 5 averaging
for RS can have up to 9 station in less than 250 km
Need L1/L2 instrument
more finicky measurement, can have rejection. After rapid orbits things improve
Accuracy less than static analogous to real time network in terms of accuracy
Normalized rms error by what thy think is a typical day

Question 23

Cors station organized

Answer 23

backup battey, satellite dish to broadcast , or urban setting internet connection to a service

CORS network in university airport government facility forestation , dense in east and west cost

useful for autonomous driven vehicles specialy rapid static

Question 24

Range calculated from gps satellite

Answer 24

c*deltaT- clock bias= square root of difference of satellite and user xyz square

Question 25

730 invention john harrison

Answer 25

problem can calculate longitude on land but not ocean

king George the third offer reward to solve problem

a clock maker comes out with an idea- if we know what time is at prime meridian and what time is where we are, we can calculate longitude, all we need 2 precise clock. One set to greenwich and the other one set to noon and monitor sun and time and set clock and look at time difference

dividing 360 degree by 24 hr every hour is 15 degree of longitude

Question 26

Laser

Answer 26

stands for light amplification by stimulated emission of radiation
useful making distance measurement, send light beam, does not diverge, known velocity so can calculate delta T and get distance
wavelength and phase relationship

Properties:
monocrmotic
collimated
coherance

Question 27

beam diversion

Answer 27

an be achieved

We use near-infrared, cannot see light, beyond your visibility, piece of metal aluminum

Question 28

Lidar

Answer 28

irst arrived in airborne system, simple controllers, against mirror that goes back and ford, put on floor of airplane or helicopter, carried over landscape the oscillating mirror allowed to hit targets that were orthogonal to site
when they got better allow Multi degree of freedom

terrestrial laser scanner placed on tripod
airborne more expensive because of the navigation system that needs to know precisely where the laser is and orientation as it flies

Question 29

Laser riscan

Answer 29

nit range of 1000 m, but far range measurement are not very useful , most data use if the first few hundred meter
Instrument error of 4mm at 1000 m range

GPS error for ellipsoid height might be 1 to 4 cm the moment we shift our data to an ellipsoid solution it will be degraded
To be an orthometric height then het 5 cm so the number will blow out

We have to register multiple scan together- point do not match perfectly there is some error in there too
we need up we total error at least 1/4 of magnitude greater than actual instrument precision

Instrument are so precise that it is the other things that are coming into place that really matter not the precision of the instrument for most applications

Question 30

why civil engineering want to use this kind of spacial data ?

Answer 30

structural- look at displacement, deflecttion, rotations, is the construction as built matching the design

More electricty, more piping, new ducts, scan room, see all utility and map them up. figure out what spaces exist

petroleum platform - open and expose and all utility and pumping fluid and electricity and they want to redisign without sshuting down

movie production, taking to set of scene that are going to be shot for movies. Plan out shooting second user

third user mine industry, fast volume calculation
Maptek gear to mining industry in australia
geotecnical engineering soil erosion, any kind deformation associated with land slide storm earthquake

Question 31

terrestial laser

Answer 31

set up
instrument , camera siting on top that gives it color
above is the differential gps devise that says so many centimeter above reference point of scanner, so we know where our scanner is on earth

set up base station to communicate with rover or use network solution

Laser pointed straight up, Plug mirror and spins, laser comes up and hits the mirror and goes out
run off a laptop and internet connection to base of unit
Out of range that is damaging to eyes

Question 32

electromagnetic spectrum

Answer 32

Change laser by frequency to achieve different colors

tune to achieved other frequencies

water penetrating green instrument need glasses to protect eyes design to filter out specific frequency

Question 33

Lidar system

Answer 33

light laser, we have a neodymium-doped yttrium aluminum garnet
oscillator set up between mirror and half mirror and image that the wave bounces out between this two units and leaves the laser and comes out as las light

Question 34

Energy of light

Answer 34

is a function of a frequency
v=f lambda  
Nd-yag 1064nm
given wave length , velocity 3*10^8 
v/1064nm =2.8*1064 cycles/sec
E=hf=hV/lambda=1.867*10^-19 J energy wave carries

Longer wavelength longer frequency then lower energy, radio wave more energy , microwave

Question 35

Class lidar laser energy

Answer 35

Riegl z420i
The amount of energy per photon is low enough that there is not risk of being blinded

airborne laser scan, beam stronger and visible an are dangerous

Question 36

Various type of reflectors that we use to do registrations

Answer 36

one version 10 cm cylinders
retro prysmas directional, need to be looking at it
unidirectional point last at 360 degree and get a return
set total station on a clift put reflector on top of the laser, and some over the total station shot on reflector where the gps unit is on top of scanner to tell us where the scanner is
another strategy is use gps unit to know where the scanner is
porpose the scanner is to just know what is in the land scape but know where the scanner is
set above vegetation, take pic of every set up, so we can unrestnd problems with data

Registration idea of taking multiple scan and bring it torether
two steps translate to another spot and rotation in xyz

Question 37

to do registration

Answer 37

put reflector out in the field, move scan to different positions, all base line length are different but relation shipp of reflector to each other have not change so we can find the best fit translation and rotation to make them fit in the least square sense

need to collect multiple scan to fill in shadows, make surface, counter map and change detection

Question 38

Problem with tripods

Answer 38

the scanner can only see what you can see, so vegetation can be a problem, ways to improve is, one way is to try to make an quasi airborne system by installing television poles, can have downward view of terrain, they are called space needles

Question 39

cylinder reflector

Answer 39

has a height and diameter, when scanned you get to the outer surface of cylinder vand there is an alogarism thatt calculate the center height go the cylinder and subtracts that from the closest distance to that cylinders to determine location
scanner sits in its own coordinate system, does not know where it is, thinks is 0,0,0 , so everything that measure is relative to 0,0,0
two scans, hold one as a reference and the other one freely moves to best match the reference

Question 40

Coordinates system

Answer 40

All individual scans that are at 0,0,0 but are pull away to a relative position from that landscape , this is called a project coordinate system
Internally is all consistent to the square best fit model but does not know where it is in earth

Last step is to translate it to global coordinating system where we take values and translating to northing and easting and elevations, typically in UTM

Question 41

Riscanpro

Answer 41

closer than two meter does not show up
define reflector circle with 3800 points
need minimum 3 reflector to triangulate location
camera to color scan
use for utilities, can show hanging light, pipeline etc can be taken to i-studio and figure out how to bring new utility to the room
movie set figure out everything you gonna do in the room before you get there

Maximum rmsc error of half a meter,

In the field take gps unit, take measure of scanner and reflector, northing easting and elevation, select list as global coordinate system list and do best fit to global coordinates

Question 42

euler and reflectors

Answer 42

n scan did translation and rotation with direction cosine matrix which is a matrix form of euler equation, and found the common best fit set of reflector between scan, sastify the least error

Question 43

euler angles

Answer 43

we do slight rotation, the sign of the sine angle will be nearly zero, cosine slightly less than 1, x’ almost entirely associated with cosine x and y’ associated with cosine of y
45 degree cosine and sine equal to each other, new x position being a composite of both x and y coordinate equally, part of the x becomes the new y component and part of original y component becalms part of the new x component

the simple translation is cd, once we add third corner of rotation we have a problem, the order of the transformation matters because you get different results. c

turn sine into cosines
turn sine into cosine by cosine x’ relative to x and y component times the sine of alpha turn into the cosine of x’y

turn matrix into cosines calculating orthogonal rotated vector

Question 44

to do rotation in 3d

Answer 44

rotating about z value xy and rotate nothing happens to z values

map out error differencing position one fix other relative moving passing we can find minimum and that is the one we accept as best

Question 45

point clouds

Answer 45

look elevation in a model, calculate hight for scans, square of the difference sum up over all increamental measurement N , and take square root of that and is the root mean square error of elevation

calculates residual -difference between the two

Minimum for mean square error — best fit solution
expenses way to do it —translate steps and then rotate

other way determine max vector at rmse is decreasing follow the path into center of ball, much faster

Question 46

What components causes liar to work faster today than an instrument used in class?

Answer 46

the one in class only 4 years old, but slower, less memory, less speed. transition is faster, step remotes one sponge mirror vertical orientation, stoping and starting, a second rotating 360 degree turn. To do it currently has to happen in a speed that is not too fast, there have been improvement at the speed remotes can do this accurately and stop and start faster. Only real difference btw the one in class and new one is speed

Question 47

is it possible to scan the entire are in riscan and do registration does it mean we don’t need to register each scan independently in maptek?

Answer 47

re register in lab to try to find the best model

Question 48

what were the sticky disk in the room?

Answer 48

all those reflectors are registration points, instead of doing global matching in maptek, we match up the reflectors.

Question 49

Least square best fit

Answer 49

omputed sum of square residual between measure value and known value

Question 50

Euler angles order

Answer 50

the order by which we do the transformation, will change the orientation.

transformation happening across from position 1 to intermediate position f’ to position f2’ then to position 2

T21 = T2F’’ TF’‘F’ TF’1

Question 51

how does least square intercepts euler

Answer 51

scan does not know how much it has to move so we have to use step progression to get it into place

taking one scan registering to a second scan t though this matrix manipulation and match them program alogarism and if fail or calculate a rmsv lower so going in the one dicrectio, we keep doing that until we find the minimum

2 scan register together, so we move from individual coordinate system to a project coordinate system, we call this a soft matrix, and then move to a global coordinate system

Question 52

Comparison between airborne and terrestrial

Answer 52

Airborne came first, step remoter were slow and difficult to do angular rotation,
laser scanner using tilted mirror has bee used for a long time but in this case we are measuring the time of flight of laser hitting the mirror, going to a target on the ground and coming back hitting the mirror and coming back to receiver

terrestrial approach is the demonstrated in class

advantage ground,
stationary - if you want to know coordinates in landscape is better to make measurement from stationary position
if you are close to the scan which mean you can put many laser point onto very small target close up

Advantage air
cover a lot of landscape and fast
but resolution is low and accuracy is also low

Question 53

trench data set, comparison

Answer 53

airborne and terrestrial
first scan from a plane with window floor
and the trenching was done with helicopter to get close to the ground

the laser range finder 2-3 cm, gps error 5-10 cm, imu error 9cm @ 900 m

Question 54

imu error

Answer 54

is one of the complication of having airborne liar data, if there is wind airplane has to flyght into it to compensate, so they flight skew pathway changing orientation, wind not always coming horizontal can come upward or downward, so airplane can be pitch up or down, turn oblique or roll. These motion complicating navigation of airplane changing orientation of the way the last moves and therefore changes the location of where the laser hits the ground
immersial motion unit (imu) make really precise measurement s of roll pitching yag to reposition point accurately on ground

IMU Many grades of quality, most acurrent systems are use for defense, ex. jet.

Add up error vendors giving a 95% confidential error of 18 cm vertical 30-40 cm for horizontal (not so great for CE applications)

Question 55

airborne systems collection

Answer 55

swaths of data, a little of overlap, error increase as we move away from beneath aircraft out to outer extend of scan, so want to have sufficient amount of overlap.

laser does a z pattern coming together at end scan and then spread apart . big gap at tail and fit closer together toward center. we try to exclude the data toward outer edges

Question 56

airborne benefit vegetation

Answer 56

airborne benefit is that uses different type of algorithm to calculate target. For our purposes we have the speed of light times time of flight over two as range between laser and ground it hits

airborne system apply optics to allow laser points span several meters called beam divergence. More complicated analysis of the return waveforms, not picking up the stronger signal but the whole return wave form signal. Useful for vegetation problem by divergent the beam, it hits top of tree and sends strongest signal, and the other option of laser continuous its way down until it makes it to the ground. hope last return is the ground.

There is a lot of processing that goes into the analysis of the last return to try to find our which one is the ground

Question 57

hurricane isabel, north carolina

Answer 57

North caroline barrier beach,
Before hurricane, barrier island, homes look degraded in airborne system, do not retain shape
Hurricane reaches though the barrier and some of the structures were lost

Question 58

cal campus unavco open topography

Answer 58

Open topography to access data,
Cal campus poorly define, looks fussy and unclear, but for a general topographic of berkeley takes 2 min to collect, so you can cover a lot of terrain quickly but not vey accurently

Question 59

trench study scan

Answer 59

Airplane -poor spot density
helicopter laserr points is better but can’t hardly get a sense that there is a trench there
terrestial data scanner, there is all the detail

Question 60

trench study stats

Answer 60

know values, standard to compare airborne is total station made by surveyors
residual calculation between known elevation and measure by lidar

Mean of distribution offsets from know value
Mean of the residual is a measure of sample bias, offset between red and blue line

dispersion how spread out from the central mean of the bias, measure of noise of data
Bias measure if there is a systematic problem in determining elevation

4sigma -+2 95 % confidence limit, expect Mui to fall between these two point

sample desperation difference between residual minus bias over all data

Question 61

root mean square error

Answer 61

difference in residual over n
large sample equal bias square minus dispersion squared
unbiased population equal to the standard deviation of residual or dispersion

Question 62

One of the problem in airborne system

Answer 62

hat you do not own the devise someone does data collection for you

for terrestial you can control and revisit if there was a problem

poor quality control in determining bias and dispersion between vendors in airborne so difference between 23 cm and 8 cm might be two different vendor and their systematic problems

Question 63

education aspect of liar

Answer 63

ability to share—virtual trip to a location

3 examples from different event
land slide- hitachinaka japan
structural damage, tilting -chile
breatching damn - japan fujinuma

Not collecting data in optimal way, without reflectors

Question 64

hitachinaka port japan

Answer 64

overlay port on google earth-road back of port became deformed and depressed in outer edge, and elevation of ground behind structure.
evidence of tsunami, scatter debris, not first floor, no walls

step up at latter skirt, buldging toe of land slide

using section ttool maptek,
see cliff no damage
head skirt-settlement
deformation of toe

no data set before earth quake so we can project surface of the road, model using polygons and use this to calculate settlement

settlement extended from 0 to 2 meters

Question 65

Concepcion chile 2010 earthquake

Answer 65

liquefaction
one building experience a lot of settlement on foundation
two building were build in one year in a densified mat and two of them build the following year on an not as well prepare foundation

first two building no deformation but the other two 2 cm below

President condominium
Worst buidling we have one corner 34 cm settlement 6.9 on the other corner so its settling and tilting over a foot

3.8-10cm settement on rest building

how do we know settlement? using a loop in maptek of one elevation and drop down to calculate the change of elevation of the corner of buildings

returned to the site in 2013 and can see the building leaning
1.5 degree tilting
2014 two buildings were demolish

Question 66

fujishima japan — dam failure

Answer 66

dam failure
agriculture dam, earthquake liquify foundation of dam and the up reservoir slid to reservoir causing after to overtop the dam, receiver had fully drained hours after earthquake

1949 dam, performed well given the age

pre event contour drawing comes based on engineering drawings

post event geometry comes from using polygons

one zone of very dense data, obtain by doing overview scan first, zoom in to get a higher resolution scan to calculate post event damage

section of dam that slid into receiver was on the order of 8m and then that left the receiver thought the gap was 8-10 meter more

Question 67

refraction

Answer 67

refraction is the speed of light in a vacuum divided the speed of light in the atmosphere
very small change
3 ten thousands but has effect on measurements

laser passing though air, velocity drops frequency remains the same so wavelength changes

refraction of speed of light on vacuum divided by speed of light in air

Question 68

aspects that affect refraction

Answer 68

atmospheric pressure -vacuum at normal atmosphere at see level causing being of light
move from high pressure moving down expect index of refraction to fall alls to zero when get to vacuum

temperature - the wavelength shorten and volesty falls as the temperature gets colder (thicker air)
temperature has the greatest effect

effect of humidity is minor
temperature is controling changes of refraction

Question 69

refraction for airborne and terrestrial

Answer 69

airborne data set, air temperature is different from temperature of ground and laser light is going through the whole range of temperatures, if there is a real temperature difference we have an uncontrolled error on our range estimate
refraction an issue obliques shots for airplane because the pathway is longer

Also another reason why in terrestrial we like data to overlap and in we use the closest data and exclude other

Question 70

one of the issue associated with refraction is

Answer 70

that affect the precision by which we can estimate the location on the ground. Refraction changes the velocity and wavelength and therefore changes our estimate of the range and is linearly proportional to the length of the shot. so the longer the shot the more accumulated errors can occur

when doing laser scan need to record temperature, and try to minimize the difference between your set up location and the target you are shutting to shorten the distance to minimize effect of refraction