cs 128/es 228 - lecture 9b1 photogrammetry & image analysis

CS 128/ES 228 - Lecture 9b 1

Photogrammetry & Image Analysis


Photogrammetry

Originally, the science (or art?) of interpreting aerial photographs

Stress on quantitative measurements

Now includes analysis of digital images from many sources

Image from Avery. Interpretation of Aerial Photographs.


A hierarchy of remote sensing

Satellite sensing

Aerial photography

Ground-truthing



Perspectives

Vertical:- orthogonal perspective- planimetric map data

Oblique: - high oblique

(includes horizon) - low oblique (no horizon)



Scale

Determine from: Plane altitude

RF = lens focal length altitude of plane

Known ground features

Top image from Avery. Interpretation of Aerial Photographs.Bottom images from Ben Meadows catalog (L), Olean NW DOQQ ®


Problems

Plane altitude determining altitude (barometer, radar altimeter) variation among photos uneven terrain

Known ground features: need objects of known size & large enough for accurate

measurement, or pair of points for distance measure


Planimetric view

Perfectly vertical (orthogonal) perspective

All features in correct horizontal positions

Impossible unless at infinite height


The principle point

Point directly under camera lens (‘nadir’)

Elevated objects lean away from PP

Depressed objects lean toward PP

Causes image displacement

Images from Avery. Interpretation of Aerial Photographs.


Vertical relief causes displacement

Transmission line is straight - why does the line appear straight in one photo and jagged in second?

In left stereogram, line is ~ on nadir; in right stereogram, far from nadir



Image displacement:

Source of error in horizontal locations, but

Permits estimation of feature elevations

stereoscopic parallax



Stereoscopic photo pairs



Stereoscopes

need pair of overlapping photos

different principle points results in parallax

used to create topographic contours


Shadows

Need sun angle

Object must be vertical

Shadow must come from top and fall on level ground

H = L x tan(α)

H = L x tan(α)

Image from Avery. Interpretation of Aerial Photographs.\


Rectification of aerial photographs

Rectification: process of geometric correction that turns an aerial photograph into a planimetric (map-like) image

Problems: lens distortion Earth curvature camera tilt terrain relief


Rectification process

1. Scan aerial photograph at high resolution

2. Locate ground control points on scanned image: ≥3 for affine transformation ≥5 for rubbersheeting

3. Combine with DEM to correct relief displacement

4. Rectify to a ground coordinate system


Relief distortion

Objects at different distances form the lens will be distorted


Result: digital orthophotograph

USGS supplies in DOQ format

NYS GIS site provides freecolored infrared DOQQs


Urban areas: building tilt

In urban areas, tall buildings seem to lean toward the principal point of the photograph

Corrected by building a DTM of each building

Permits virtual reality “flyovers”

Thorpe, A. Digital orthophotography in New York City. www.sanborn.com/Pdfs/Article_DOI_Thorpe.pdf


Image Analysis

Identification of objects

Assigning attributes to objects or areas

Assessing the significance of patterns

Can be: Visual interpretation

Computer-assisted image analysis


Landsat Images

Landsat 1-4 launched 1972 – ’82; expired

Landsat 5 & 7 launched 1985 & 1999; both operational

TM: thematic mapper. - 7 spectral bands- designed primarily for ES themes

http://landsat.gsfc.nasa.gov/project/L7images.html


TM Applications

Band Spectral range (µm)

“Color” Application

1 0.45 – 0.52 Blue-green Soil/vegetation separation

2 0.52 – 0.60 Green Reflection from vegetation

3 0.63 – 0.69 Red Chlorophyll absorption

4 0.76 – 0.90 Near IR Delineation of water bodies

5 1.55 – 1.75 Mid IR Vegetative moisture

6 10.4 – 12.5 Far IR Hydrothermal mapping

7 2.08 – 2.35 Mid IR Plant heat stress


Hydrology example

Images from Avery. Interpretation of Aerial Photographs.


Terra (and EOS)

Terra launched

Carries 5 instruments; the MSS imager is called ASTER (from Japan)

14 spectral bands:- 3 VIS/near IR (15 m)- 6 short IR (30 m)- 5 thermal IR (90 m)

Images from www.nasa.gov


ASTER spectral signature library

“Welcome to the ASTER spectral library, a compilation of almost 2000 spectra of natural and man made materials.”

http://speclib.jpl.nasa.gov


Classification schemes

1.a Unsupervised: raw data analyzed for clusters

1.b Supervised: prior categories imposed

2. Classification of new data

3. Ground truthing … Lo & Yeung. Concepts and Techniques of Geographic Information Systems


And that’s the fun part …

cs 128/es 228 - lecture 9b1 photogrammetry & image analysis

Documents

lecture 9b3

lecture 9b8

aerial photographs stress

nadir image

horizon image

sources image

lecture 9b2 photogrammetry

infinite height slide