AVHRPANO

Description

Performs a panoramic correction of an AVHRR image that has been imported into PCIDSK format. After a panoramic correction, an AVHRR image can be geometrically corrected with fewer ground control points using the REG function. Only HRPT or LAC AVHRR images with widths of 2048 pixels can be corrected.

Parameters

Name	Type	Caption	Length	Value range
FILI *	String	Input file name	1 - 192
FILO *	String	Output file name	1 - 192
DBIC	Integer	Input raster channel(s)	0 -
DBOC	Integer	Output corrected channel(s)	0 -	Default: 1,2,3,4,5
RESAMPLE *	String	Resample mode:	3 - 5	NEAR|BILIN|CUBIC|8PT|16PT Default: NEAR
MEMSIZE	Float	Working memory size (MB)	0 - 1	Default: 0.25

* Required parameter

Parameter descriptions

FILI

Specifies the name of the input file that contains the raw AVHRR image data.

This is typically a PCIDSK file created using FIMPORT or MIAVHRR, but FILI may also be a Level 1b AVHRR disk file.

FILO

Specifies the name of the PCIDSK file to receive the corrected image data.

If the specified output file does not already exist, it is created. Because the image width expands, FILO cannot be the same as FILI.

DBIC

Specifies the input channels containing ACHRR images to correct.

Input channels must contain 2,048 pixels. If this parameter is not specified, the entire image is processed by default.

Ranges of channels or segments can be specified with negative values. For example, {1,-4,10} is internally expanded to {1,2,3,4,10}. When you are not specifying a range in this way, only 48 numbers can be specified explicitly.

DBOC

Specifies the output channels in the ouput file (FILO) to receive the corrected image(s).

Duplicate output channels are not allowed. Output channels must contain at least 2,964 pixels.

The total number of input channels (DBIC) must be equal to the total number of ouput channels specified here.

If this parameter is not specified, the output channels are set from 1 to the total number of channels in the input file.

Ranges of channels or segments can be specified with negative values. For example, {1,-4,10} is internally expanded to {1,2,3,4,10}. When you are not specifying a range in this way, only 48 numbers can be specified explicitly.

RESAMPLE

Specifies the resampling method to use during the registration process.

MEMSIZE

Specifies the amount, in megabytes, of internal memory allocated to AVHRPANO.

The default is 0.25 MB; a typical amount of memory to allocate is approximately half of the system memory available per processing thread.

Details

AVHRPANO prepares raw AVHRR image data for subsequent geometric correction by the REG function. It expands the input image so that fewer ground control points (GCPs) are required to perform a geometric correction. Typically, approximately 40 GCPs are needed to geometrically correct a 2048 x 2000 pixel image to 1-pixel accuracy; after a panoramic correction, however, the number of GCPs that are required is reduced to approximately 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 layer must contain at least 2964 pixels in order to receive the entire panoramic image.

Example

Perform a panoramic correction of a 5-channel AVHRR image by using the Nearest Neighbor interpolation method.

EASI>fili	=	'avhraw.pix'
EASI>filo	=	'avhpano.pix'
EASI>dbic	=	1,2,3,4,5	! input channels
EASI>dboc	=		! defaults to dbic
EASI>resample	=	'NEAR'	! nearest neighbor
EASI>memsize	=		! defaults to 0.25 MB

EASI>RUN AVHRPANO