Geometric Correction ital for many applications using remotely sensed images to know the ons for points in the image. There are two similar processes that ca the link between images and real world locations: image-to-map recti age-to-image registration. o-map rectification: a process by which the geometry of an image is etric with reference to a projected map. o-image registration: a process which translate the geometry of one ther (usually projected) image so that corresponding elements of the area appear in the same place on the registered images. The image u nce (with known projection and coordinates) is called the master ima age to be registered is called the subject image. mportant that the reference map or image is rendered in a standard m tion and coordinate systems.
15
Embed
Geometric Correction It is vital for many applications using remotely sensed images to know the ground locations for points in the image. There are two.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Geometric Correction
It is vital for many applications using remotely sensed images to know the ground locations for points in the image. There are two similar processes that can help build the link between images and real world locations: image-to-map rectification and image-to-image registration.
Image-to-map rectification: a process by which the geometry of an image is made planimetric with reference to a projected map.
Image-to-image registration: a process which translate the geometry of one image to another (usually projected) image so that corresponding elements of the same ground area appear in the same place on the registered images. The image used as reference (with known projection and coordinates) is called the master image, and the image to be registered is called the subject image.
It is important that the reference map or image is rendered in a standard map projection and coordinate systems.
Map Projection
Map projection is the process of systematic transformation of points on the Earth’s surface to corresponding points on a plane surface.
Cylindrical
Conical
Planar
Commonly Used Spheroid in Map Projection
Ellipsoids Date Semi-major axis Semi-minor axis Ellipticity
Many of the earlier US maps are based on Clarke 1866 ellipsoid which was determined by Sir Alexander Clarke in 1866. The World Geodetic System (WGS72 and 84) ellipsoids, determined from satellite orbital data are considered more accurate.
GRS80 (Geodetic Reference System) ellipsoid is adopted by the International Association of Geodesy
The Global Coordinate System
spherical coordinate system
unprojected!
expressed in terms of two angles (latitude &
longitude)
longitude: angle formed by a line going from the intersection of the prime meridian and the equator to the center of the earth, and a second line from the center of the earth to the point in question
latitude: angle formed by a line from the equator toward the center of the earth, and a second line perpendicular to the reference ellipsoid at the point in question
latitudepositive in n. hemisphere
negative in s. hemisphere
longitudepositive east of Prime Meridian
negative west of Prime Meridian
Origin of Geographic Coordinate System
Global Coordinate System
The Universal Transverse Mercator Coordinate System
60 zones, each 6° longitude wide
Starting from 180 degrees eastward
zones run from 80° S to 84° N
poles covered by Universal Polar System (UPS
Transverse Mercator Projection applied to each 6o zone to minimize distortion
UTM Zone Projection
UTM Coordinate Parameters
Unit: metersZones: 6o longititue
N and S zones: separate coord
X-origin: 500,000 m east of central meridian
Y-origin: equator
USA In The UTM Zones
State Plane Coordinate System
• Each state has one or more zones• Zones are either N-S or E-W oriented (except Alaska)• Each zone has separate coordinate system and appropriate projection
• Unit: feet no negative numbers
Map Projections for State Plane Coordinate System
N-S zones: Transverse Mercator Projection
E-W zones: Lambert conformal conic projection
Geometric Correction
x’
y’
x
y
image map
GCP
GCP
),(
),(
2
1
yxfy
yxfx
Ground Control Points
Master x Master y Subject x Subject y
x1 y1
x2 y2
x3 y3
… …
x1 y1
x2 y2
x3 y3
… …
Note: Coordinates must be in file coordinates (lines, samples).
First order polynomial:
ybxbby
yaxaax
210
210
Second order polynomial:
25
243210
25
243210
ybxbxybybxbby
yaxaxyayaxaax
Third order polynomial …
Goodness of fit:
n
iiiii yyxx
nRMSE
1
22 )()(1
Unit of RMSE: pixels
Image Grids on Reference Grids
The output of geometric correction is a grid that exactly overlays the reference grid.
Image-to-map rectification: Need to create a reference grid first. (1). Specify an origin (2). Translate map coordinates to image coordinates based on pixel size.
Resampling Methods
1. Nearest Neighbor: The DN values in the output grid takes from the pixel that is nearest in the input grid. The output grid maintains all the original DN values in the input grid. 2. Bilinear Interpolation:
4
12
4
12
1
k k
k k
k
D
D
DN
BVInverse distance weighted average of the four nearest pixels to the output pixel.
3. Cubic Convolution:
16
12
16
12
1
k k
k k
k
D
D
DN
BVInverse distance weighted average of the 16 nearest pixels to the output pixel.