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Stereoscopic vision
This document discusses stereoscopic vision and its use in aerial photo interpretation. Stereoscopic vision involves using binocular vision to view overlapping photos from two camera positions to perceive 3D depth. Various stereoscopes can be used, like lens stereoscopes suitable for field use. Key measurements for determining object heights from stereo pairs include the average photo base length and differential parallax. Precise stereoplotters and software can digitally recreate stereo models for mapping. Orthophotos rectify photos to show objects in true planimetric positions.
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Stereoscopic vision
- 1. Stereoscopic Vision FOR 220 AerialPhoto Interpretation and Forest Measurements
- 2. • The picturesused 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 useof 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 binocularoptical 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 ofStereoscopes: Mirror stereoscope Photos can be placed separately for viewing Used in the field?
- 6. Stereoscopic Vision Types ofStereoscopes: Scanning mirror stereoscope A series of lenses and prisms Relatively expensive Not used in the field
- 7. Stereoscopic Vision Types ofStereoscopes: Zoom stereoscope Variable magnification: 2.5 - 20 x Very Expensive Not used in the field The “Cadillac” of stereoscopes
- 8. Stereoscopic Vision Types ofStereoscopes: 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 2photographs 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, RutgersUniversity
- 11. Rick Lathrop, RutgersUniversity
- 12. Rick Lathrop, RutgersUniversity
- 13. Rick Lathrop, RutgersUniversity
- 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 + × = )( dPP dPH h
- 15. Stereo Photograph Geometry 1.Determine average photo-base (P) Average distance between PP and CPP for stereopair Example: if then P1 = 4.5 in. P = 4.4 in. P2 = 4.3 in. P1 PP CPP P2 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 db = 2.06 in. dP = 0.6 in. dt = 1.46 in. Measurments for parallax height calculations: PP CPP PPCPP db dt
- 17. Stereo Photograph Geometry Usingthe 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 dPH h
- 18. Stereo Photograph Geometry Parallaxcalculations 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 - precisioninstruments 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 andrelief 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 meterpixel size Georectified to UTM Panchromatic Some Color Infrared Scale 1:24000 DOQ of Mammoth Springs, Yellowstone National Park