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	Length	Value range
Input: Input geocoded channel(s) *	Raster port	1 - 3
Background No-Data Value	Integer	0 - 3
InputRaw: Raw image file name	Raster port	0 -
InputMM: Math model segment number	BIN port	0 - 1
InputOrbit: Orbit segment number	ORB port	0 - 1
InputGCP: Ground Control Point segment	GCP port	0 - 1
Chip Database *	String	1 -
Chip Sensor Type	String	0 - 1
Chip Date	String	0 - 1
Chip Size	Integer	0 - 2	Default: 64
Number of Chips *	Integer	1 - 1	1 - 50000
Chip Rejection Variance	Float	0 - 1
InputDEM: Input elevation channel	Raster port	0 - 1
Background Value in Elevation Layer	Float	0 - 1
Cloud Rejection Threshold	Float	0 - 2	Default: 255,100

* Required parameter

Parameter descriptions

Input: Input geocoded channel(s)

Specifies the input channels in the geocoded file.

Background No-Data Value

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

InputRaw: Raw image file name

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.

InputMM: Math model segment number

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.

InputOrbit: Orbit segment number

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.

InputGCP: Ground Control Point segment

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.

Chip Database

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.

Chip Sensor Type

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.

Chip Date

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.

Chip Size

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.

Number of Chips

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

Chip Rejection Variance

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.

InputDEM: Input elevation channel

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

Background Value in Elevation Layer

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 the Elevation Channel is specified and this parameter is not, all pixels are valid elevation values. This parameter is used only if an elevation channel is specified.

Cloud Rejection Threshold

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.