AVHRPANO -- AVHRR Panoramic Correction

Performs a panoramic correction of an AVHRR image which has been imported into PCIDSK format. After a panoramic correction, an AVHRR image can be geometrically corrected using less ground control points with programs such as REG and GCPWORKS.

Only HRPT or LAC AVHRR images with widths of 2048 pixels can be corrected.

See Also: AVHRCOR, FIMPORT, GCPWORKS, GDB, MIAVHRR, REG

PARAMETERS

AVHRPANO is controlled by the following global parameters:

Name     Prompt                                  Count     Type
FILI     Database Input File Name                1-64      Char
FILO     Database Output File Name               1-64      Char
DBIC     Database Input Channel List             1-1024    Int
DBOC     Database Output Channel List            1-1024    Int
RESAMPLE Resample mode:  NEAR/BILIN/CUBIC        4         Char
MEMSIZE  Working Memory Size (Mbytes)            0-1       Int

FILI

Specifies the name of the input file containing the raw AVHRR image data. Typically, this is a PCIDSK file created using FIMPORT or MIAVHRR. However, FILI can also be an actual Level 1b AVHRR disk file.

 EASI>FILI="filespec1"

FILO

Specifies the name of the PCIDSK file to receive the corrected image data. FILO will be created if it does not already exist. FILO cannot be the same as FILI due to image width expansion.

 EASI>FILO="filespec2"

DBIC

Specifies the list of input channels to be read from FILI.

 EASI>DBIC=i,j,k, ...

Up to 1024 channels can be specified.
Up to 16 integer values can be specified.
Ranges of channels can be specified by using negative values. For example, {1,-4,10} is internally expanded to {1,2,3,4,10}.
Input channels must contain 2048 pixels

If DBIC is not specified, DBIC values will be set from 1 up to the total number of channels in the input file.

DBOC

Specifies the list of channels to be output to FILO.

 EASI>DBOC=i,j,k, ...

Up to 1024 channels can be specified.
Up to 16 integer values can be specified.
Ranges of channels can be specified by using negative values. For example, {1,-4,10} is internally expanded to {1,2,3,4,10}.
Duplicate output channels are NOT allowed.
Output channels must contain at least 2964 pixels.

The total number of channels specified by DBIC must be equal to the total number of channels specified by DBOC.

If DBOC is not specified, DBOC values will be set from 1 up to the total number of channels in the input file.

RESAMPLE

Specifies the desired type of resampling of image data. The following methods are supported:

 EASI>RESAMPLE="NEAR"    | Nearest Neighbour
 EASI>RESAMPLE="BILIN"   | Bilinear Interpolation
 EASI>RESAMPLE="CUBIC"   | Cubic Convolution
 EASI>RESAMPLE="8PT"     | Sin(x)/x with a  8 x  8 window
 EASI>RESAMPLE="16PT"    | Sin(x)/x with a 16 x 16 window

MEMSIZE

Specifies the size in Mbytes of internal working memory for AVHRPANO. In general AVHRPANO will run faster with larger amounts of memory.

 EASI>MEMSIZE=n                  | use n Mbytes
 EASI>MEMSIZE=                   | use default value of 0.25 Mbytes

DETAILS

AVHRPANO prepares a raw AVHRR image for subsequent geometric correction by a program such as REG or GCPWORKS. It expands the input image in such a way that fewer ground control points (GCPs) are required for performing a geometric correction. Typically, around 40 GCPs are needed to geometrically correct a 2048 x 2000 pixel image to 1 pixel accuracy. However, after a panoramic correction, the number of GCPs required is reduced to around 10.

AVHRPANO georectifies an AVHRR image using a cosine^2 deviations algorithm. A vector of multiplication factors is computed and pixels are replicated according to the numbers in this vector. The factors are based on the fact that the AVHRR sensor's field of view (110.8 degrees) is sampled into 2048 pixels during scanning. The output channel must contain at least 2964 pixels in order to receive the entire panoramic image.

EXAMPLE

Example 1:

Perform a panoramic correction of a 5 channel AVHRR image using a nearest neighbour interpolation method.

 EASI>FILI="AVHRAW.PIX"
 EASI>FILO="AVHPANO.PIX"
 EASI>DBIC=1,2,3,4,5
 EASI>DBOC=                      | Defaults to 1,2,3,4,5
 EASI>RESAMPLE="NEAR"
 EASI>MEMSIZE=                   | Defaults to .25
 EASI>RUN AVHRPANO

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