GCPWRIT

Description

The GCPWRIT algorithm reads ground control points (GCP) from a specified GCP segment or layer and writes the GCP coordinates to a text file.

Parameters

Name	Type	Caption	Length	Value range
FILE *	String	File name of input image	1 - 192
DBGC *	Integer	Input GCP segment or layer	1 - 1
TFILE *	String	Output text file	1 - 192
GCPFORM *	String	Format of GCP data	1 - 64	2D, 2DERR, 3D, 3DERR, BULK Default: 3D
DMSFORM	String	Degrees-minutes-seconds (DMS) format of longitude and latitude	0 - 3	ON, OFF Default: OFF

* Required parameter

Parameter descriptions

FILE

The name of the PCIDSK file that contains the GCP segment from which to read the GCP data.

DBGC

The input GCP layer or segment to read.

TFILE

The path and file name of the output text file to which to write the GCP coordinates.

For more information on the required format for the text file, see the description of the GCP format (GCPFORM) parameter.

Important: A file with the same name must not exist in the folder you specify.

GCPFORM

The code for the format of the input GCP data.

The codes are described as follows:

2D: ID P L X Y S
2DERR: D P L X Y eP eL eX eY S
3D: ID P L X Y Z S
3DERR: ID P L X Y Z eP eL eX eY eZ S
BULK: ID S X Y Z PhotoID P L PhotoID P L ...

where:

ID: true GCP or check point GCP ID
P, L: pixel and line values
X, Y, Z: georeferenced x, y, and z values
eP, eL: pixel and line error values
eX, eY, eZ: x, y, and z error values
S: "G" for active GCPs, "I" for inactive GCPs, and "C" for check-point GCPs
PhotoID: Image ID that corresponds to the pixel and line coordinates of each GCP

DMSFORM

Whether the output coordinates of longitude and latitude use real numbers or degrees/minutes/seconds/hemisphere strings.

OFF: output of degrees is signed real numbers. This is the default value.
ON: write latitude and longitude values to the output text file in DMS format. Apostrophe (') and quotation (") symbols are used as separators between degrees, minutes, seconds, and hemisphere

This parameter is ignored if vector units are not LONG/LAT.

The DMS format for latitude and longitude is as follows:

latitude: [integer degrees]d[integer minutes]'[floating point seconds]"[N|S]
longitude: [integer degrees]d[integer minutes]'[floating point seconds]"[E|W]

where N, S, E, and W stand for the north, south, east, and west hemispheres, respectively.

For example:

latitude: 34d01'15.1104"N
longitude: 118d14'14.2080"W

Note: When the latitude and longitude values are written as floating-point numbers, the unit is degrees. A positive (negative) latitude is in the northern (southern) hemisphere, and a positive (negative) longitude is in the eastern (western) hemisphere.

Details

The GCPWRIT algorithm writes GCP data from a specified GCP segment or layer to a text file. The GCP data may include check-point data. To specify the format of the GCP data in the output text file, you use the GCP format (GCPFORM) and Deg/Min/Sec format (DMSFORM) parameters.

A GCP may be intended for use with georeferencing control (a "true GCP"), or it may be intended for use in assessing the accuracy of a rectification result (a "check point" or a "check-point GCP"). The data written to the output text file includes a flag value (S) that distinguishes between the two.

Example

Read GCP data from GCP segment 27 in the file "irvine.pix" and write the data to the newly created file "gcp.txt" in format "2D". Latitude and longitude values will be written as signed floating-point numbers.

EASI>FILE = 'irvine.pix'
EASI>DBGC =	"27"
EASI>TFILE = 'gcp.txt'
EASI>GCPFORM = '2D'
EASI>DMSFORM = ''
                    
EASI>r gcpwrit

Environments	PYTHON :: EASI :: MODELER
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