CHIPEXT

Description

CHIPEXT automatically extracts chips from a geocoded image to a chip database. The number of chips extracted is based on a uniform distribution and a maximum number that the user specifies.

Parameters

Name	Type	Caption	Length	Value range
GEOFILE *	String	Geocoded file name	1 - 192
DBIC *	Integer	Input geocoded channel(s)	1 - 3
BACKVAL	Integer	Background gray-level value	0 - 3
FILE	String	Raw image file name	0 - 192
MMSEG	Integer	Math model segment number	0 - 1
ORBIT	Integer	Orbit segment number	0 - 1
DBGC	Integer	Ground Control Point segment	0 - 1
CHIPFILE *	String	Name of chip database	1 - 192
CHIPSENS	String	Sensor Origin of GEOFILE	0 - 16
CHIPDATE	String	Acquisition date of geocoded file	0 - 21
CHIPSIZE	Integer	Size of chips (pixel, line)	0 - 2	Default: 64
NUMCHIPS *	Integer	Maximum number of chips	1 - 1	1 - 50000
CHIPSIGM	Float	Chip rejection variance	0 - 1
FILEDEM	String	DEM file name	0 - 192
DBEC	Integer	Input elevation channel	0 - 1
BACKELEV	Float	Background elevation value	0 - 1
CLOUDTHR	Float	Cloud rejection threshold (DN, % of cloud content)	0 - 2	Default: 255,100

* Required parameter

Parameter descriptions

GEOFILE

Specifies the name of the geocoded file from which the chips are extracted.

DBIC

Specifies the input channels in the geocoded file.

BACKVAL

Specifies the background (no-data) value of the geocoded file. If this parameter is not specified, all pixels are considered valid data.

FILE

Specifies a PCIDSK file that contains a raw scene (layer). If this parameter is specified, CHIPEXT only extracts image chips from the overlap area between the raw and the geocoded file. To find the overlap area, the raw image must have approximate geocoding information available; this is possible if you specify a Math Model Layer, Orbit Layer, or GCP Layer for the file.

MMSEG

Specifies a math model segment for the raw image. All math model types are supported.

This parameter can establish the approximate geocoding information for the raw image.

ORBIT

Specifies an orbit segment that contains ephemeris information for the raw image.

This parameter can establish the approximate geocoding information for the raw image.

If no orbit segment is found, CHIPEXT uses the input file's georeferencing information.

DBGC

Specifies a ground control point (GCP) segment that contains georeferenced information.

This parameter can establish the approximate geocoding information for the raw image. If empty, the last segment is used.

CHIPFILE

Specifies the name of the chip database in which to store the extracted chips. If the database already exists, the new chips are appended to it. If it does not already exist, a new CDB file is created.

CHIPSENS

Specifies a sensor name. This is a free format that may be used later to select appropriate chips.

If the GEOFILE parameter is empty, do not specify a sensor name.

CHIPDATE

Specifies the date that the geocoded file was acquired.

A regular expression for chip dates (ddmmmyyyy) is accepted; for example, 02Mar2006. This parameter may be used later to select chips that match an appropriate time period.

CHIPSIZE

Specifies the size of each extracted chip, in pixels and lines. The default size is 64 x 64. Because this parameter accepts up to two values, rectangular chips can be extracted. When only one value is provided, square chips result.

NUMCHIPS

Specifies the maximum number of chips that are extracted. Maximum number is 50000.

CHIPSIGM

Specifies the variance threshold for chip rejection. Any chip with a variance of less than the specified threshold is discarded. The default value is 0.0.

FILEDEM

Specifies a name for the DEM file that extracts the elevation value of the extracted chip. If this parameter is not specified, no elevation value is extracted.

DBEC

Identifies the channel that contains the elevation data to be extracted.

DBEC is used only if FILEDEM is specified. If FILEDEM is specified without DBEC, the first channel is used.

BACKELEV

Specifies the background elevation value (or no-data value) in the DEM elevation layer. If the center of a chip falls on a pixel with this value, it is ignored.

If FILEDEM is specified and BACKELEV is not, all pixels are valid elevation values. BACKELEV is used only if FILEDEM is specified.

CLOUDTHR

Specifies the minimum gray-level value that is treated as clouds in an extracted chip and the percentage of cloud content in which the extracted chip is rejected (DN, % of cloud content).

By default, a gray-level value of 255 and 100 percent of cloud content is used for rejection.

Details

CHIPEXT extracts image chips from a geocoded file to a chip database, based on the number of chips and a uniform distribution. The extracted chips are stored in a chip database (CHIPFILE). This chip database may be used for future image tie-down or automatic geocoding.

You may specify a raw PCIDSK file to limit the area of extraction to overlap the scene. If this file is specified, CHIPEXT extracts image chips from the overlap area between the raw file and the geocoded file. To find the overlap area, the raw scene must have approximate geocoding available. To find the geocoded information, you must enter a math model segment, an orbit segment, or a ground control point (GCP) segment. If multiple values are specified, the MMSEG value takes precedence, then ORBIT, and finally DBGC. If no value is specified and the program requires one, the last segment of MMSEG is used, then the last of ORBIT, and so on. This information is then used to establish a geocoding location of the raw image and to locate the overlapping region on the geocoded image.

If background values (no-data value) exist in the geocoded image, you must specify this value (BACKVAL). Chips with background values are ignored.

You may specify a chip sensor (CHIPSENS) and acquisition date (CHIPDATE) for the geocoded file; these can be used later in automatic geocoding to select chips that match the appropriate information.

To perform automatic geocoding, the chip must contain enough heterogeneous content. This can be controlled by specifying the minimum rejection variance in the chip (CHIPSIGM). Any chip with a variance less than the specified CHIPSIGM value is rejected.

To perform orthorectification in a future process, you must extract the elevation of the chip by specifying a digital elevation model file (FILEDEM) with an elevation channel (DBEC).

Satellite images typically contain clouds, which can cause failure in automatic geocoding. A cloud rejection threshold (CLOUDTHR) helps to reject chips with clouds. CLOUDTHR allows you to specify the minimum gray-level value that is treated as clouds in a chip, and the percentage of cloud content at which the extracted chip is rejected.

Example

Extract a maximum of 100 chips from "OSPOTR.PIX" and create a new chip database name "geocodedSourcePPF.cdb".

EASI>GEOFILE     =   "OSPOTR.PIX"
EASI>DBIC        =   1
EASI>BACKVAL     =   0
EASI>FILE        =   "SPOTLEFT.PIX"
EASI>MMSEG       =   4
EASI>ORBIT       = 
EASI>DBGC       = 
EASI>CHIPFILE    =   "geocodedSourcePPF.cdb"
EASI>CHIPSENS    =   "SPOT"
EASI>CHIPDATE    =   "15Sep1999"
EASI>CHIPSIZE    =   64,64
EASI>NUMCHIPS    =   100
EASI>CHIPSIGM    =   50
EASI>FILEDEM     =   "SPOTDEM.PIX"
EASI>DBEC       =   1
EASI>BACKELEV    = 
EASI>CLOUDTHR    =   200,20

EASI>RUN CHIPEXT