Suveying Last Class

8/13/2019 Suveying Last Class

1/26

Principles of Photogrammetry:

Stereoscopic Parallax


2/26

Stereophotography

Adjacent but

overlapping aerial

photos are calledstereo-pairs and are

needed to determine

parallax and stereo/3D

viewing


3/26

Overlapping Stereophotography

Overlapping

photography

Endlap - ~60%

Sidelap - ~20-30%


4/26

Relief Displacement

Even from great flying

heights, tall objects can

exhibit image displacement.

In this example from aQuickbird satellite image,

the Washington Monument

appears to lean outwards


5/26

Radial Displacement

Objects will tend tolean outward, i.e. be

radially displaced.

The greater the object

is from the principalpoint, the greater the

radial displacement.

Example: storagetanks towards the edge

of photo show greater

radial displacement.

Center of

photo

Edge of

photo


6/26

Maps vs. Aerial Photos

Maps: Scale is constant

No relief displacement

Photos: Scale varies with elevation

Relief displacement


7/26

Stereoscopic Parallax

The displacement ofan object caused by a

change in the point of

observation is called

parallax.

Stereoscopic parallax

is caused by taking

photographs of thesame object but from

different points of

observation.


8/26

Stereoscopic parallax

Line of Flight

Note the displacement between the top and base ofthe storage towers in this photo stereo-pair

top

bottom


9/26

Stereoscopic Plotting Instruments

Stereoplotters - precision

instruments designed to

duplicate the exact relative

position and orientation of

the aerial camera at thetime of photo acquisition

to recreate the stereo-

model. A floating mark

can be used trace specificelevations. Relief

displacement is removed

creating a planimetric

map.


10/26

Stereoscopic Plotting Instruments

Soft-copyphotogrammetry

workstations - computer

software recreates the

stereomodel and allowsfor digital mapping

Soft-copy

photogrammtery has

largely replaced optical-mechanical systems

Digital

scanner

Soft copy

workstation


11/26

Simulated 3-D Stereo viewing

One view displayed in red; the otherperspective view in blue spatially shifted

The spatial shift is a

function of thedifferential parallax

To visualize, use

red-blue glasses

NASA Mars Lander


12/26

Electronic Distance Measurement


13/26

Got its start in 1948 with Swiss device using

visible light (range=40km only at night)http://www.gmat.unsw.edu.au

Microwaves used in 1957 (range=80km)http://www.gmat.unsw.edu.au

Infra-red, IR, devices are common todayhttp://www.pentaxcanada.ca


14/26

Electro-magnetic energy travels through the

atmosphere according to the following:

Where:

c = speed of light in vacuum

n = atmospheric index of refraction, 1.003 for STP

f = frequency of the electro-magnetic energy

l= wavelength of the energy

c/n=fl


15/26

So called total-station instruments package a

digital theodolite (for measuring azimuth andaltitude) with an EDM, data storage device, and

often a modem for transmitting data from the

field. The most common instruments use a pulse of 2

to 4 AM frequencies ranging from 150kHz to

15MHz. This range of frequencies have corresponding

half-wavelengths of 1.0km to 10m,

respectively.

http://www.nikon.co.jp/survey-e


16/26

12/19/2013

It is a combination of an electronic theodolite(transit), an electronic distance meter (EDM) andsoftware running on an external computer known as adata collector.

A total station is an optical instrument used inmodern surveying and archaeology as well as by

police, crime scene investigators, private accidentreconstructionists and insurance companies to takemeasurements of scenes.


17/26

12/19/2013

Salient features of modern TS

TS is a fully integrated equipment that captures all the spatial

data necessary for a three-dimensional position fix. The angles anddistances are displayed on a digital readout and can be recorded at the

press of a button. Total station is usually operated by a surveyor assisted

by a labourer or geodesist who carries the target pole to the points of

detail to be surveyed. Various components of a typical TS are shown inFig.6.

Fig. 6 Parts of Total Station


18/26

12/19/2013

Electronic transitReads andstores horizontal and vertical

angles

Uses EDM to measure and store

the distance of points

Points can be stored in the

instrument using computer

fig.7Total station


19/26

12/19/2013

EDM Electronic theodolite

On-Board Micro-processor

Data Collector

Data Storage

Prisms

Abhilasha P S, VAST 19


20/26

12/19/201320

Distance units are in metres.

IR mode has high accuracy, long range,

and measures to a specific point.

Personal access is required to the targetpoint.


21/26

12/19/2013Abhilasha P S, VAST 21

Reflector less moderequires no prism.

Range up to 160m.

Distance units are in metres

Reflector less mode can measure to inaccessiblepoints, but be careful about pointing and beam

interruptions!


22/26


HD = SD * Sin(VA)

VD = SD * Cos(VA)

SDVA

IH

TH

The inbuilt software computes the HD and VD from

the SD and the VA


23/26


Application pre-settings

F1 = Name of jobF2 = Name of setup station

F3 = Orientation

F4 = Begin


24/26



25/26

12/19/2013

Advantages of Total Station over

Conventional instruments:

Traditional survey methods are laborious and time

consuming

Fully automatic electronic measurement

Digital display of staff reading and distance

Data storage in instrument possible

Direct transfer to personal computer of data stored in

instruments

Online operation through integrated interface to computer

Abhilasha P S, VAST 25


26/26

12/19/2013

Disadvantages

Total stations are dependent on batteries and electronics. The

LCD screen does not work well when it is cold.

Battery life is also short, batteries and electronics both do not

work well when wet.

Loss of data is an important consideration.

Abhilasha P S VAST 26

Documents

Suveying Last Class