Stereoscopic vision

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Stereoscopic Vision 0 Aerial Photo Interpretation and Forest Measurements

Transcript of Stereoscopic vision

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StereoscopicVision

FOR 220 Aerial Photo Interpretation and Forest Measurements

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• The pictures used in the stereo views where in the form of "stereographs" which were two pictures of the same scene that were slightly offset and mounted side-by-side.

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Stereoscopic Vision

StereoscopyThe use of binocular vision to achieve 3-dimensional effects.

Enables you to view an object from 2 different camera positions to obtain a 3-dimensional view.

Stereo pairs of photographs

Two adjacent, overlapping photographs in the same flight line.

Stereo views can only be seen in the overlapping portion of the photos.

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Stereoscopic Vision

Stereoscopes:A binocular optical instrument that helps us view two properly oriented photos toobtain a 3-dimensional model.

Types of Stereoscopes:

Lens (pocket) stereoscope

Simplest Least expensive Small 2-4 x magnification Used in the field

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Stereoscopic Vision

Types of Stereoscopes:

Mirror stereoscope

Photos can be placed separately for viewing

Used in the field?

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Stereoscopic Vision

Types of Stereoscopes:

Scanning mirror stereoscope

A series of lenses and prisms

Relatively expensive

Not used in the field

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Stereoscopic Vision

Types of Stereoscopes:

Zoom stereoscope

Variable magnification: 2.5 - 20 x

Very Expensive

Not used in the field

The “Cadillac” of stereoscopes

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Stereoscopic Vision

Types of Stereoscopes:

Zoom transfer stereoscope

Variable magnification: 2.5 - 20 x

Used to transfer features from a stereo-pair of photos onto a map or other photo

Very Expensive

Not used in the field

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1. Obtain 2 photographs consecutively marked on a flight line.

2. Locate and mark the Principal Points on each photograph.

3. Locate and mark the Conjugate Principal Points on each photograph.

4. Line up all 4 points and adjust the distance between photographs to suit your needs.

Stereo Photograph Geometry

Orientation of Stereo Pairs

Flight Line

Note “photo-crab”

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Rick Lathrop, Rutgers University

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Rick Lathrop, Rutgers University

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Rick Lathrop, Rutgers University

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Rick Lathrop, Rutgers University

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Stereo Photograph Geometry

Where:h = object height H = flying heightdP = differential parallax P = avg. photo base length (avg. distance, PP to CPP)

** Above equation is for level terrain only.

General formula for calculating height using parallax

)( dPP

dPHh

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Stereo Photograph Geometry

1. Determine average photo-base (P)

Average distance between PP and CPP for stereopair

Example: if thenP1 = 4.5 in. P = 4.4 in.P2 = 4.3 in.

P1

PP CPP

P2

PPCPP

Measurements for parallax height calculations:

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Stereo Photograph Geometry

2. Determine differential parallax (dP)

Difference of the distances between feature bases and tops while stereopair is in stereo viewing postion.

Example: if thendb = 2.06 in. dP = 0.6 in.dt = 1.46 in.

Measurments for parallax height calculations:

PP CPP PPCPP

db

dt

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Stereo Photograph Geometry

Using the measurements from previous slides, “plug and chug”

h = object height (we want this) H = flying height (2,200 ft. given in flight information) dP = differential parallax (0.6 in.= 2.06in. - 1.46in.) P = avg. photo base length (4.4 in.) (avg. distance, PP to CPP)

Example: Computing height using stereoscopic parallax

Solve for h:h = (2,200 ft. * 0.6 in.) / (4.4 in. + 0.6 in.) = 1320 ft. in. / 5 in. = 264 ft.

)( dPP

dPHh

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Stereo Photograph Geometry

Parallax calculations of height are useful where the object of interest is:

On small scale photographs (high altitude flight)

Located at or near the nadir of a single photo.

Obscured on one photo of a stereopair, but the base and top can still be located.

Flight or camera variables (except aircraft height) are not known.

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Stereoplotters - precision instruments designed to duplicate the exact relative position and orientation of the aerial camera at the time of photo acquisition to recreate the stereo model. A floating mark can be used trace specific elevations. Relief displacement is removed creating a planimetric map.

Soft-copy photogrammetry workstations - computer software recreates the stereo model and allows for digital mapping

Stereo Photograph Geometry

Stereoscopic Plotting Instruments

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Photographic distortion and relief displacement are removed during orthorectification

Orthophoto - rectified aerial photo showing objects in their true planimetric position

Orthophotoquad - orthophoto in the standard USGS 7.5 minute quadrangle format with same scale accuracy as USGS topographic maps

DOQ – digital orthophoto quad

DOQQ - digital orthophoto quarter quad

“Native” format of orthophotos is digital

Stereo Photograph Geometry

Orthophotography

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Digital Orthophotograph

1 meter pixel size

Georectified to UTM

Panchromatic

Some Color Infrared

Scale 1:24000

DOQ of Mammoth Springs, Yellowstone National Park