Stereoscopic vision

Stereoscopic vision,Measurements for parallax height calculations,Stereoscopic Plotting Instruments,

1. Stereoscopic
Vision
FOR 220 Aerial Photo Interpretation and Forest Measurements

2. •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.

3. Stereoscopic Vision
Stereoscopy
The 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.

4. Stereoscopic Vision
Stereoscopes:
A binocular optical instrument that helps us view two properly oriented photos to
obtain a 3-dimensional model.
Types of Stereoscopes:
Lens (pocket) stereoscope
Simplest
Least expensive
Small
2-4 x magnification
Used in the field

5. Stereoscopic Vision
Types of Stereoscopes:
Mirror stereoscope
Photos can be placed separately
for viewing
Used in the field?

6. Stereoscopic Vision
Types of Stereoscopes:
Scanning mirror stereoscope
A series of lenses and prisms
Relatively expensive
Not used in the field

7. Stereoscopic Vision
Types of Stereoscopes:
Zoom stereoscope
Variable magnification:
2.5 - 20 x
Very Expensive
Not used in the field
The “Cadillac” of stereoscopes

8. 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

9. 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”

10. Rick Lathrop, Rutgers University

11. Rick Lathrop, Rutgers University

12. Rick Lathrop, Rutgers University

13. Rick Lathrop, Rutgers University

14. Stereo Photograph Geometry
Where:
h = object height
H = flying height
dP = 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
÷
÷
ø
ö
ç
ç
è
æ
+
´
=
)(dPP
dPH
h

15. Stereo Photograph Geometry
1. Determine average photo-base (P)
Average distance between PP and CPP for stereopair
Example: if then
P
1
= 4.5 in. P = 4.4 in.
P
2
= 4.3 in.
P
1
PP CPP
P
2
PPCPP
Measurements for parallax height calculations:

16. 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 then
d
b
= 2.06 in.dP = 0.6 in.
d
t
= 1.46 in.
Measurments for parallax height calculations:
PP CPP PPCPP
d
b
d
t

17. 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.
÷
÷
ø
ö
ç
ç
è
æ
+
´
=
)(dPP
dPH
h

18. 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.

19. 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

23. 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

24. Digital Orthophotograph
1 meter pixel size
Georectified to UTM
Panchromatic
Some Color Infrared
Scale 1:24000
DOQ of Mammoth Springs,
Yellowstone National Park