Post on 13-Dec-2015
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Stereovision and Photo Stereovision and Photo InterpretationInterpretation
3-dimensional viewing of aerial photos
How does stereo vision work?How does stereo vision work?
Each eye views the same feature from a difference Each eye views the same feature from a difference angle/perspective and the brain fuses the images into angle/perspective and the brain fuses the images into a single coherent imagea single coherent image
The greater the distance between viewing stations The greater the distance between viewing stations (eye base or photo base) the better the depth (eye base or photo base) the better the depth perceptionperception
There is vertical exaggeration when viewing aerial There is vertical exaggeration when viewing aerial photos with a stereoscope photos with a stereoscope
With a stereoscope the relationship between With a stereoscope the relationship between accommodation (ability of eyes to change focus based accommodation (ability of eyes to change focus based on distance to an object) and convergence is on distance to an object) and convergence is unnaturalunnatural
Not everyone can see in stereoNot everyone can see in stereo There are exercises to develop the ability to see in There are exercises to develop the ability to see in
stereostereo
Tools for stereoscopic Tools for stereoscopic interpretationinterpretation
Aerial photo stereo pairsAerial photo stereo pairs StereoscopeStereoscope Transparency to protect photosTransparency to protect photos Pens or other markersPens or other markers Pin to prick holes to mark principle pointsPin to prick holes to mark principle points Tape or weights to hold photos to tableTape or weights to hold photos to table Good lighting Good lighting Interpretation key to aid in identifying Interpretation key to aid in identifying
featuresfeatures i.e., i.e., http://www.treesearch.fs.fed.us/pubs/6451http://www.treesearch.fs.fed.us/pubs/6451
Measuring tools (parallax bar, ruler)Measuring tools (parallax bar, ruler)
StereoscopesStereoscopes
Pocket stereoscopesPocket stereoscopes Handy for use in the fieldHandy for use in the field Simple and inexpensive (~$5 – 100)Simple and inexpensive (~$5 – 100) Cumbersome when working with large format Cumbersome when working with large format
photographyphotography Mirror stereoscopesMirror stereoscopes
Usually large enough to easily view 23cm photosUsually large enough to easily view 23cm photos Come with additional lenses for magnified viewingCome with additional lenses for magnified viewing Quality ranges from simple (~$140) to precise Quality ranges from simple (~$140) to precise
(~$3,000)(~$3,000) Mirrors can be very delicate and require special Mirrors can be very delicate and require special
carecare
Mirror stereoscope Pocket
stereoscope
Orientation of stereo photosOrientation of stereo photos
Verify photos are consecutively numbered and Verify photos are consecutively numbered and there is at sufficient forward overlapthere is at sufficient forward overlap
Orient photos so shadows fall toward the observer Orient photos so shadows fall toward the observer to reduce pseudoscopic effectto reduce pseudoscopic effect
Locate the principal point and the conjugate Locate the principal point and the conjugate principal point for each photoprincipal point for each photo
Align the two photos using a ruler so the 4 points Align the two photos using a ruler so the 4 points are on the same lineare on the same line
Tape or put weights on the photos to hold them in Tape or put weights on the photos to hold them in placeplace
Overlay with transparency to protect photos and Overlay with transparency to protect photos and mark fiducial marks and photo reference mark fiducial marks and photo reference
Viewing stereo photos on a Viewing stereo photos on a computercomputer
Photos must be properly oriented before Photos must be properly oriented before viewing and this requires special software viewing and this requires special software such as ERDAS Leica Photogrammetry Suitesuch as ERDAS Leica Photogrammetry Suite
Viewing the georeferenced stereo pairs Viewing the georeferenced stereo pairs requires special software such as Stereo requires special software such as Stereo Analyst Analyst
Viewing on the screen can be done using:Viewing on the screen can be done using: Red and blue anaglyph glassesRed and blue anaglyph glasses LCD shutter glasses (requires special graphics LCD shutter glasses (requires special graphics
card)card) Polarized screen and glassesPolarized screen and glasses