30 Questions
What is the leading cause of geometric distortion in vertical aerial photography?
Relief displacement
Why are objects directly below the center of the camera lens affected in aerial photography?
Because they lean away from the center of the photo
What role does terrain relief play in causing geometric distortion?
It contributes to geometric distortion
In aerial photography, why are objects at the nadir position only showing their tops?
Due to relief displacement
Which factor influences objects appearing to lean away from the center of an aerial photograph?
Terrain relief
How do framing systems like cameras used for aerial photography capture images?
By producing 'snapshot' views from directly overhead
What type of distortion results in the compression of image features at points away from the nadir?
Tangential Scale Distortion
Which scanning system distortion causes the sweep of scanning systems to cover an area slightly to the west of each previous scan?
Skew Distortion
Which platform type helps alleviate geometric distortions by providing relatively stable orbits?
Satellite platforms
Which factor influences geometric distortions caused by variations in platform stability?
Changes in speed, altitude, and attitude
What causes imagery obtained from satellite multispectral scanners to exhibit skew distortion?
Eastward rotation of the Earth during a satellite orbit
How are geometric distortions and positional errors affected by the distance of objects from the center of a photo?
They increase
What is the primary purpose of geometric correction in digital images?
To compensate for distortions introduced by various factors
Why are raw digital images usually not suitable for direct use as a map base?
Because they contain significant geometric distortions
Which of the following is NOT a source of geometric distortions in digital images?
Sensor resolution
What is the role of image data providers in the context of geometric correction?
They automatically perform all necessary corrections
How are systematic distortions typically corrected in digital images?
By applying mathematical formulas derived from modeling the sources of distortions
What is the key consideration before attempting to make measurements or extract further information from digital images?
The necessity of considering and addressing errors in the images
What is the purpose of least-squares regression analysis in the context of the given text?
To determine coefficients for transformation functions.
Which equations are used to interrelate geometrically correct (map) coordinates and distorted-image coordinates?
$x = f1 (X,Y) y = f2 (X,Y)$
How are the distorted-image coordinates of any map position estimated?
By determining coefficients for transformation equations.
What does the process of 'resampling' involve in the context of the text?
Assigning intensity values based on transformed positions.
What determines the intensity value or digital number assigned to a cell in the output matrix during resampling?
The pixel values surrounding its transformed position.
In general, why does a cell in the output matrix not directly overlay a pixel in the input matrix during resampling?
To account for pixel values from surrounding positions.
What is the purpose of image registration?
To map one image onto another using a perfect transformation
What is the role of feature detection in image registration?
To extract key features and distinctive objects from images
How do area-based methods differ from feature-based methods in feature matching?
Feature-based methods estimate control points for perfect matches, while area-based methods match predefined size.
What does the mapping function do in the image registration process?
Reconstructs the sensed image
In what manner is a sensed image typically registered in transformation and resampling?
Forward transformation
What is the main objective of comparing reference and sensed images with control points in image registration?
To significantly influence the registration process
Study Notes
- Remote sensing images acquired from various platforms/sensors have inherent geometric distortions due to factors like sensor optics, platform motion, altitude, and Earth's curvature.
- Aerial photography systems like cameras can cause relief displacement, where objects away from the camera's center appear distorted in vertical aerial photography.
- Across-track scanning systems exhibit tangential scale distortion compressing features away from the nadir and skew distortion due to the eastward rotation of the Earth.
- Geometric correction is essential to compensate for distortions in raw digital images caused by factors like platform variations, earth curvature, and atmospheric effects.
- Systematic distortions are easily corrected using mathematical formulas and regression analysis to transform distorted-image coordinates into map coordinates.
- Resampling is a process used to determine pixel values in the output matrix from the original image matrix during geometric correction.
- Image registration involves mapping one image onto another using a perfect transformation, including feature detection, matching, designing mapping functions, and transformation/resampling processes.
Learn about the geometric distortions present in remote sensing images captured through satellite, aircraft, or other sensor platforms. Understand how these distortions affect the representation of Earth's surface in a two-dimensional image.
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