Stereoscopic vision

StereoscopicVision

FOR 220 Aerial Photo Interpretation and Forest Measurements

• 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.

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.

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

Stereoscopic Vision

Types of Stereoscopes:

Mirror stereoscope

Photos can be placed separately for viewing

Used in the field?

Stereoscopic Vision

Types of Stereoscopes:

Scanning mirror stereoscope

A series of lenses and prisms

Relatively expensive

Not used in the field

Stereoscopic Vision

Types of Stereoscopes:

Zoom stereoscope

Variable magnification: 2.5 - 20 x

Very Expensive

Not used in the field

The “Cadillac” of stereoscopes

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

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”

Rick Lathrop, Rutgers University

Rick Lathrop, Rutgers University

Rick Lathrop, Rutgers University

Rick Lathrop, Rutgers University

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

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:

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

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

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.

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

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

Digital Orthophotograph

1 meter pixel size

Georectified to UTM

Panchromatic

Some Color Infrared

Scale 1:24000

DOQ of Mammoth Springs, Yellowstone National Park