february 3 interpretation of digital data bit and byte ascii binary image recording media and...
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February 3
Interpretation of Digital Data
Bit and ByteASCIIBinary
Image Recording Media and Formats
Geometric correctionsImage registration
Projections
Computer Basics(1)Bit and byte
1 bit 0-1 21
0 1
2 bit 0-3 22
3 bit 0-7 23
One bit in computer requires one register– a switch between 0 and 1
0 1 2 3
0 1 2 3
4 5 6 7
5 bit 0-31 25
4 bit 0-15 24
6 bit 0-63 26
7 bit 0-127 27
8 bit 0-255 28
One byte has 2 =256 combinations with 8 registers. It therefore can be used to specifyLetter, arabics and symbols up to a total of 256
Computer Basics
2. ASCII file (text file) (American Standard Code for Information Interchange)
101 102 103
201 202 202
111 112 113
12 bytes
12 bytes
12 bytes
Each digit uses one byte. One byte is required between two numbers andat the end of a line or file.
Information on an image, such as date, location, level of processing, solar zenith angle, view angle, etc., are usually contained in ASCII format i.e., header of an image file.
Computer Basics
2. binary file
101 102 103
201 202 202
111 112 113
3 bytes
3 bytes
3 bytes
Advantage of binary files: (i) less memory requirement, (ii) fast reading and saving operations
Remote sensing images are commonly stored in binary files
Disadvantage of binary files: (i) content can’t be displayed as text,
(ii) the information can not be retrieved without knowing the image format, i.e., # of bits/datum, pixels/line, # of lines
Packing Multispectral Data(1) Band interlived by pixel (BIP) : data are stored pixel by pixel for all bands
simultaneously21 86 34 28 31 89 21 ……
Band 1
Band 2
Band 3
Band 4
16 18 21 32 19 18 21 ….
08 06 04 03 06 09 10 12 …..
06 03 02 08 10 21 19 16 …..
In a binary file:
21 16 08 06 86 18 06 03 34 21 04 02 ………
Pixel (1,1) Pixel (2,1) Pixel (3,1)
Packing Multispectral Data(2) Band interlived by line (BIL): data are stored line by line for all bands
simultaneously21 86 34 28 31 89 21 ……
Band 1
Band 2
Band 3
Band 4
16 18 21 32 19 18 21 ….
08 06 04 03 06 09 10 12 …..
06 03 02 08 10 21 19 16 …..
In a binary file:
Band 1 line 1, band 2 line 1, band 3, line 1, band 4, line 1, band 1 line 2, band 2 line 2, ……
Packing Multispectral Data(3) Band sequential (BSQ) : data are stored one image (band) by one image
21 86 34 28 31 89 21 ……Band 1
Band 2
Band 3
Band 4
16 18 21 32 19 18 21 ….
08 06 04 03 06 09 10 12 …..
06 03 02 08 10 21 19 16 …..
In a binary file:
band 1, band 2, band 3, band 4
Geometric Distortions
Sources: variations in altitude and velocity of sensor platform
panoramic distortion, earth curvature, atmosphericrefraction, relief displacement, and nonlinearitiesin the swath of a sensor’s field of view (FOV)
Campbell chapter 10Lillesand-Kiefer 7.2
Geometric corrections compensate for the distortionintroduced by these factors so that the corrected images
will have geometric integrity.
Image distortions: nonsystematic
Campbell 8.7
Earth rotation Altitude variation Pitch variation
Spacecraft velocity Roll variation Yaw Variation
Distorted image Restored image
Image distortions: systematic
Cross-track distortion Mirror velocity variation Scan skew
TimeM
irror
ang
le Actualvelocity
Nominalvelocity
Image Matching
(1) Overlay of two images
(2) Registration of two images (or one image to a map)
(3) Analytical registration of two images
Campbell 10.5
Projections and re-sampling
No re-sampling
Ground control points and re-sampling
Registration
Find the same features, Ground Control Points (GCPs), on two images or on one image and a map.
GCPs can also be takenduring field experiments with
Global Positioning Systems (GPS).
GPS is a US Military satellite-based navigation systemthat uses at least three satellites to calculate a position.
Verbyla Chap. 5Campbell 12.7
Choice of Ground Control Points
From Maps and GPS
Road intersections
Rivers
Water bodies
Campbell 10.6
Image Rectification models
Verbyla Chap. 5
LinearY = AX + B
Residual Errors
X
Y
Affine Coordinate Transformations
Y’ = AX + BY + C
X’ = DX + EY + F
Polynomial Models
Y’ = A + BX + CY + DX2 + EY2 + FX3 +GY3 +...
How many GCPs?
Polynomialorder
First
Second
Third
Minimum Numberof GCPs Required
Verbyla Chap. 5
3
6
10
PCI: GCPWorks
Distorted Restored
Sabins, Chapter 8
Geometric Correction
Output Image Original Image
Campbell 10.6Lillersand-Kiefer 7.2
In general, a pixel in the output image will not directly overlay a pixel in the original image
What valueswill the pixels in
output image have?
Nearest Neighbour Bilinear Interpolation(weighted average)
Re-sampling
Campbell 10.6
Cubic Convolution(weighted average)
Re-sampling
Campbell 10.6
Most widely used
Map Projections
Campbell 10.7Verbyla Chap. 5
Satellite Images that cover large areas need map projections because of the Earth’s spherical surface.
It is impossible to project a spherical surface ontoa flat sheet without distortions to theshape, area, distance, and direction
of the surface features.
Universal Transverse Mercator Coordinates
Campbell 10.715.3-15.4
Zones of 6 degrees wide (east-west)zone 1 is at 180-174o WFrom 84o N to 80o S in latitude
Projections
Polar azimuthal (planar) Regular conic
Sabins, Chapter 8