midterm 2nd lesson Flashcards
Employs polynomial regression equations of different
degrees to relate image coordinates and their
corresponding map coordinates
POLYNOMIAL
A form of rectification that corrects for terrain
displacement using a DEM of the study area
ORTHORECTIFICATION
Use methods based on statistical operations:
“Ground Control Point rectification” _________________
(Star & Estes
1990).
The distance between the GCP reference
coordinate and the curve is expressed as the
__________________________
Root Mean Square Error (RMSE)
Due to time taken to build an image as the
sensor scans the earth surface features
Earth Rotation
is the application of a coordinate
system in the image
RECTIFICATION
refers to assigning map
coordinates to image data
Georeferencing
In relatively flat areas, this is not necessary, but
in mountainous areas (or on aerial photographs
of buildings), where a high degree of accuracy is
required.
ORTHORECTIFICATION
Because data are sampled at regular intervals,
this produces ________ distortion
along-scan distortion
Forms the preparatory phase for later analysis
Image Rectification and Restoration
(Pre-Processing)
uses the weighted average
of 16 pixels to resample
the image; the processing
is significantly the slowest
Cubic Convolution
To correct image data for distortions or
degradations that stem from the image acquisition
process
Image Rectification and Restoration
(Pre-Processing)
can be used on very distorted
aerial photographs
4th-order transformations
__________, by definition, involves
__________, since all map projection systems
are associated with map coordinates.
rectification, georeferencing
The mirror scanning rate is usually not constant
across a given scan, producing along-scan
geometric distortion
Mirror Scan Velocity Variance
The process of correcting non-linear distortions is also known
as ___________.
rubber-sheeting
The warping fits triangles to the irregularly spaced
GCPs and interpolates values to the output grid.
TRIANGULATION
The image is stretched to fit most of the coordinates.
Rubber-sheeting
Errors are given as________ error
that denote difference between output location for a
GCP and the real coordinates for the same point
when the point is recalculated via a matrix of
transformation
RMS(Root Mean Square)
registration involves
georeferencing only if the reference image is
already georeferenced
Image-to-image
To perform RST warping, you need ________________
GCPs.
three or more
The ground area imaged is proportional to the
tangent of the scan angle rather than to the angle
itself
Panoramic Distortion
e.g. Adjust DNs for effect of hazy atmosphere
Radiometric correction or preprocessing
If the speed of the platform changes, the ground
track covered by successive mirror scans changes,
producing along-track scale distortion
Platform Velocity
Due to spacing of detectors and regular sampling
Panoramic Distortion
can be used to convert Lat/Lon
data to a planar projection, for data covering a large area (to
account for the Earth’s curvature), and with distorted data
(for example, due to camera lens distortion).
2nd-order transformations
effect of platform position and attitude variations
altitude
spacecraft velocity
pitch
roll
yaw
Correcting for geometric distortions due to sensor-Earth
geometry variations (e.g. Earth’s rotation), and
conversion of the data to real world coordinates (e.g.
latitude and longitude) on the Earth’s surface.
Geometric correction
Statistical approach establishes mathematical
relationship between image coordinates and their
corresponding map coordinates using standard
statistical procedures by means of a GCP data set.
GCP Rectification
the distances between the source
and retransformed coordinates in one direction
shown for each GCP.
Residuals
Many factors contribute to the distortions, what are these?
▫ Cross-track scan error
▫ Curvature of the earth
▫ Panoramic distortion
▫ Scan Skew
▫ Earth rotation
▫ Platform velocity
▫ Mirror scan velocity
- ___________________ arise from
▫ Sensor system’s attitude, velocity, and altitude
▫ Can be corrected only through the use of ground
control points (GCPs)
▫ In particular, topographic, or relief displacement
due to terrain variation is usually the most serious
of the displacement types, especially in
mountainous terrain
Non-systematic distortions
Caused by the forward motion of the platform
during the time required for each mirror sweep.
The ground swath is not normal to the ground
track but is slightly skewed, producing cross
scan geometric distortion
Scan Skew
The geometric distortions inherent in remote
sensing images fall into two categories, what are these categories?
systematic distortions
non-systematic distortions
are used with distorted aerial
photographs, on scans of warped maps and with radar
imagery
3 rd -order transformations
-the simplest method of warping
RST (Rotation, Scaling, and Translation)
Use of __________ – points that can be
identified in the image whose exact location is
known in chosen coordinate system
“control points”
the weighted average
(linear interpolation) of the DNs for the four
pixels surrounding the transformed output pixel
is used.
Bilinear Interpolation
This triangle-based rectification should be used
when other rectification methods such as
polynomial transformation and photogrammetric
modeling cannot produce acceptable results.
Rubber-sheeting
This type of distortions can be rectified using data
from platform ephemeris and knowledge of internal
sensor distortion.
Systematic distortion
A function of the distance from the sensor to the
target, the IFOV, and the scan angle off nadir
Cross-track Scan Error
No remote sensing images are free of geometric
distortions and an essential requirement for
integrated processing of remote sensing images
and data from geographic information systems
(GIS) is that they are spatially referenced.
GEOMETRIC DISTORTIONS
the transformed pixel takes
the value of the closest pixel in the pre-shifted
array without interpolation
Nearest Neighbor
Can be corrected using a “rubbersheet”
rectification based on ground control points
TERRAIN-RELATED DISTORTION
