27 Flashcards
Definition of photogrammetry
Science of obtaining informations from photographs
2 major area of photogrammetry specialization
Metrical (determining spatial information)
Interpretative (recognizing objects)
What is the most frequently applied approach in surveying (photogrammetry)?
Metrical photogrammetry using aerial photographs (photo from aircraft)
Advantages of photogrammetry
Fast collecting spatial data
Low cost
Easy obtaining topographic details, especially in inaccessible area
Reduced the possibility losing details in data
The most used aerial cameras in metrical photogrammetry
Single-lens frame cameras
Exposing the entire frame at the same time through a lens held at fixed distance
Ex: Digital Mapping Camera (DMC)
Single lens frame camera components
Shutter and diaphragm: control interval and time the light passes the lens
Lens: gathers incoming light rays and bring them to the focal plan
Focal plane: surface where the film lies (sometimes replaced by Charge-Coupled Device in digital cameras
Types of aerial photographs
Vertical (camera axis aimed vertically downward)
Oblique (seldom used in metrical surveying)
What is not true orthographic projection but isna perspective views?
Vertical photographs
Relief displacement
The displacement of an object’s image point from its origin location caused by the object’s relief.
Relief displacement formula
RD =rh/H
r = the distance between the principal point to the point of relief displacement
h = the height of the tower
H = the flying height above the datum
Building radially outward to the principal point (magnitude increases with greater distance)
Relie displacement
The bigger the elevation difference,the bigger the relief displacement
Apparent displacement of the position of an object due to the displacement in the point of observation
Parralax
Points closer to camera (the higher elevation), will……
Move faster and have greater parallaxes
Application of parallax
Stereoscopic viewing
What is stereoscopic viewing
Placing two overlapping photos on the table and using a stereoscope (left eye see left image, so do right eye)
Coordinate systems of analytical photogrammetry (types and goal)
Image coordinates (xy) - if digital, pixel coordinates (rc)
Image space coordinates (xyz)
Ground space coordinates (XYZ)
goals: to find real word position (XYZ) from filmed photo (xy)
Interior and exterior orientation
Interior orientation: defines the internal geometry of a camera (based of focal length)
Exterior orientation: defines the position and orientation of the camera (based on the coordinates)
The collinearity condition
Exposure center, image point, ground point should lie in one straight line (applied to all)
Based on …… and … XYZ can be known and 3D model can be established
Collinearity condition and all the corresponding equations
