lsit rls review seminar: photogrammetry - c.ymcdn.com · lsit rls review seminar: photogrammetry...

17
1 John Cahoon Certified Photogrammetrist President Kenney Aerial Mapping, Inc. 4008 North 15 th Avenue Phoenix, AZ 85015 602-258-6471 [email protected] www.kam-az.com LSIT RLS Review Seminar: Photogrammetry Definition of Photogrammetry MANUAL OF PHOTOGRAMMETRY Fourth Edition: “ Photogrammetry is the art, science and technology of obtaining reliable information about physical objects and the environment through processes of recording, measuring, and interpreting photographic images and patterns of electromagnetic radiant energy and other phenomena.” Aircraft: Cessna 206 Turbo Charged Typical Aerial Mapping Aircraft

Upload: vohanh

Post on 20-Apr-2019

251 views

Category:

Documents


6 download

TRANSCRIPT

1

John CahoonCertified Photogrammetrist

President

Kenney Aerial Mapping, Inc.

4008 North 15th Avenue

Phoenix, AZ 85015

602-258-6471

[email protected]

www.kam-az.com

LSIT RLS Review Seminar:

Photogrammetry

Definition of Photogrammetry

MANUAL OF PHOTOGRAMMETRY Fourth

Edition:

“ Photogrammetry is the art, science and technology

of obtaining reliable information about physical

objects and the environment through processes of

recording, measuring, and interpreting photographic

images and patterns of electromagnetic radiant

energy and other phenomena.”

Aircraft:

Cessna 206 Turbo Charged

Typical Aerial Mapping Aircraft

2

• Forward Motion Compensation(FMC)

• Gyro Stabilized Mount

Zeiss RMK TOP 15 Camera

Components of a Metric Aerial Camera

1) Lens Cone Assembly

2) Camera Body

3) Magazine

Additional Components

Camera Controls (Video, Computers)

Viewfinder, Navigation Equipment

Forward Motion Compensation

Mount, Gyro Stabilized

Components of a Metric Aerial Camera

3

Interior of a Metric Aerial Camera

The Metric Mapping Camera

9” x 9” Negative Size

6” focal length

Calibrated for Mapping

8 fiducial marks

are used to

calculate photo

coordinates and

are a vital part of

the aero

triangulation

process.

Types of Aerial Photographs

�Vertical Photograph

– Optical axis is vertical in relation to the ground

�Oblique Photograph

– Optical axis is purposely tilted

– High Oblique

• Apparent horizon is shown

– Low Oblique

• Apparent horizon is not shown

4

Flying Height

� Generally from 1000’ to 20000’ above sea level

for small single and twin engine aircraft

�Land with very high elevations reduces our

ability to obtain small scale photography

� Average flying height above ground defines the

photo scale

� The relationship of flying height to photo scale

is linear

� Double the flying height will double the photo

scale, but it covers 4 times the area.

Photographic Scale

�A function of Flying Height above mean terrain

Expressed as AGL, AMT

�Flying Height above mean sea level

Expressed as MSL, ASL

�Photographic Scale as a ratio

1:7200 means 1 part in 7200: 1m = 7200m

�7200/12 (inches per foot) expresses the scale in

inches to feet.

7200/12=600 or 1”=600’

Photographic Scale

�Photo Scale is Uniform Across the Photo if:

– It is a truly vertical photograph

– Ground is flat across the entire photograph

�Photo Scale varies due to tilt and elevation changes

in the ground.

– A truly vertical photograph with flat terrain will

have a constant scale.

– If the ground elevation varies the scale will vary.

5

Scale Variations Due to Terrain

Photographic Scale

�The Relationship between :

– Focal Length of the Camera ( f )

– Flying Height (H)

– Elevation of a point, line or area above or below

the AGL (h)

Scale = f

H - h

Photographic Scale Determination

• Average Scale

– Measure in any area of the photo

– Gives approximate values in relatively flat

ground

hav = Average elevation of the area

ScaleA = f

H - hav

6

Relief Displacement

�“The displacement of the image of a ground point

on a photograph from the position the image would

have if the point were on the datum”

�Due to the elevation of the ground point being

above or below the datum

�Amount depends on the position of the point on the

photograph

Relief Displacement in Mountainous Terrain

This property is

roughly a square.

The terrain height

increases

dramatically to the

NW and the image

is displaced

outward.

Relief Displacement in Urban Terrain

The effect on

urban high rises

is similar.

Building tops are

displaced

outward from

the photo center

or nadir.

7

Relief Displacement

�At the principal point equals zero

�Increases radially outward towards the edge of the photo

�Increases as the elevation of the point increases

�Decreases as the elevation of the point decreases

�Straight lines are displaced outward as they go over ridges

� Straight lines are displaced inward as they cross gullies

� Straight radial lines are straight but the distance is not

accurate

� Straight tangential lines exhibit the most displacement

Relief Displacement

d = Relief Displacement

r = Radial Distance From Principal Point

h = Elevation Of Point Above Datum

H = Flying Height Above Datum

d = rh

H

The Tilted Vertical Photograph

�There are no truly vertical aerial photographs

�Photo Scale varies across a tilted photograph

�Relief displacement increases outward from nadir

�Omega Phi Kappa system defines 3 photo tilt angles with

respect to the ground XYZ coordinate system

• Omega rotates around the X axis - Aircraft Wing to Wing

• Phi rotates around the Y axis - Aircraft Nose to Tail

• Kappa rotates around the Z axis – Swing or Crab

• These completely define the relationship between the tilted

photograph and the ground reference system

8

The Tilted Vertical Photograph

� If you know the accurate locations of the XYZ

coordinates at the calibrated principal point with

respect to the project datum for each of the two

photographs in a stereopair and

� If you know the accurate rotation variables for

each of the two photographs in a stereopair at the

instant of exposure and

� If you have interior orientation parameters from

the camera calibration report then

� You have a valid photogrammetric solution for

that stereopair.

The Collinearity Condition

�A bundle of rays from

point A projects through

the image plane to the

exposure station as a

straight line.

�An “infinite” number

of points are all subject to

the collinearity condition.

� x and y equation for

any photo image point.B C

Nadir

Stereoscopic Viewing

� An optical illusion produced by viewing three

dimensional objects on overlapping photography

� Left eye sees the object only on the left photo

� Right eye sees the object only on the right photo

� The brain reconstructs the parallactic angle between

the two objects and is forced to perceive the 3D

or Z axis of the object

�Vertical Exaggeration is caused by the lack of

equivalency between the air base to the eye base.

9

Stereophotography

�Photos that overlap produce stereo photography. 60% is the

standard overlap for mapping. The amount of overlap is

referred to as forward gain or end lap.

�Adjacent flight lines must overlap also. This is called side

lap. 30% is the standard for side lap.

�The area of overlap between two frames is generally

referred to the stereo model.

�A standard 9x9” frame with 60% forward gain and 30%

side lap has an approximate 3.6” x 6.5” area called the

neat model where accurate measurement is possible.

�X dimension = The photo scale in feet x 3.6” forward gain.

�Y dimension = The photo scale in feet x 6.5” = swath.

The Base Height Ratio

� Base: The distance between photo centers in a

flight line (principal and conjugate points)

� Height: Flying height above mean terrain

� B/H = .6 for aerial cameras with a 6” focal length

60% overlap - equal to forward gain

� Assumed that B/H is within about +\- 3%

� Linear relationship with flying height

� PE = (G-B/G) x 100

C Factor Calculation

Flying Height Divided by Contour Interval - H/C

Example: 1:3600 photo scale and a 1’ contour interval

3600/12 = 300 then 300 x 6 = 1800 (H) or

3600 x .5 = 1800= flying height

1800 / 1 = 1800 then C Factor = 1800

C Factor is a guideline, not a rule. You can select higher C

Factors depending on the type of terrain and other project

parameters. The C Factor should rarely exceed about 2200.

ASPRS allows up to a 2000 C Factor for Class 1 mapping

when using analytical and softcopy stereoplotters.

Most firms use an 1800 C Factor for most projects.

10

Stereophotography

Forward gain is defined

as the distance between

the principal point and

the conjugate principal

point.

Principal Point

Conjugate Principal

Point

Space Intersection by Collinearity

“The calculation of the

object space coordinates of

a point from its coordinates

in two or more images.”

Viewing a Stereo Pair

Image Overlap

ImageOverlap

(((in stereo)))

Produced by ERDAS

11

� National Map Accuracy Standards (1947)

90% HORIZONTAL FEATURES 1/50 OF MAP SCALE

90% SPOT ELEVATIONS AT ONE QUARTER C. I.

90% CONTOURS AT ONE HALF C. I.

� ASPRS Class 1 Standards (1990)

CHANGE TO EVALUATION BY RMSE:

HORIZONTAL RMSE OF 1/100 OF MAP SCALE

SPOT ELEVATION RMSE OF ONE SIXTH OF THE C. I.

CONTOUR RMSE OF ONE THIRD OF THE C. I.

� National Standard for Spatial Data Accuracy (NSSDA 1998)

� Arizona Spatial Data Accuracy and Georeferencing

Standards June, 2008

Ground Control for Stereomodel Orientation

To solve for the six variables per photograph

Full Field Control - 5HVP per Model

Control for Aerotriangulation ~ 1 HVP / 2 Models

Control for Airborne GPS ~ 1 HVP / 10 Models

� Much less ground control is needed

� Each photo center becomes a control point

� Fast turnaround time and reduced costs

� Suitable for two foot contour accuracy

12

A Sixty Model Block Using

Analytical Aerotriangulation - 30 Control Points

A Sixty Model Block Using Four

Control Points, Two Base Stations

And Airborne GPS

13

Conventional Control Layout for Strip Mapping

Control Layout for GPS Assisted Strip Mapping

Mapping Limits

5280’x5280’

Horizontal & Vertical Ground Control Point

Flight Planning Example

Photo Scale: 1” =

500’

Forward Gain =

1800’

2 Flight Lines x 3

Models Each

3000’ = AGL

Mapping Limits

Horizontal & Vertical Ground Control Point

Pass Point: XYZ Calculated by AT

Tie Point : XYZ Calculated by AT

2 Flight Lines

4 Models Each

Aerotriangulation Aerotriangulation

is the process

which ties strips

and blocks of

photos together

mathematically

and transforms

the image

coordinate

system to the

ground

coordinates.

14

Zeiss P3 Analytical Stereoplotter

Digital Photogrammetric Workstation

2D Planimetric Features

15

A DTM in Very Irregular Terrain

Rendering of a TIN Surface

Contours and Spot Elevations

16

3D Planimetric Features

Digital Orthophotography

Removes the 3 distortions associated with imagery.

–Aircraft tip/tilt/crab

–Camera Lens

–Terrain Displacement

Yields imagery with the same level of accuracy

as the topographic mapping

Digital Orthophoto with Planimetric Detail and Contours Superimposed

17

Automated People Mover

Hoover Dam Bypass Bridge Cranes