VECREG

Description

Performs registration of vector data using a ground control point (GCP) or georeferencing segment to produce a new segment of transformed vector data.

Parameters

Name	Type	Length	Value range
Input: Input vector segment *	Vector port	1 - 1024
InputGCP: Input GCP segment	GCP port	0 - 1
Output: Input GCP segment	Vector port	0 - 1
Regression Order	Integer	0 - 1	-1 - 5 Default: 1
Transformation Direction	String	0 - 1	FORW | BACK Default: FORW
Vector Layer Name	String	0 - 1
Vector Layer Description	String	0 - 1

* Required parameter

Parameter descriptions

Input: Input vector segment

Specifies the vector segment to be transformed.

InputGCP: Input GCP segment

Specifies the segment that contains the ground control points. The GCP segment is used to generate the polynomial transformation, allowing the vector data to be mapped to a corrected form. If this parameter is not specified, VECREG uses the georeferencing segment (number 1) to perform a first-order transformation on the vector data.

Output: Input GCP segment

Specifies the output segment to receive the transformed vector data.

Regression Order

Specifies the ORDER to use for the regression model that will fit uncorrected-to-corrected GCP coordinates, or uses a -1 flag indicating that a thin plate spline transformation should be used.

To obtain good results, it is best to have two or three times the minimum number of GCPs for a particular ORDER (for example, 12 to 18 GCPs for 2nd ORDER) and the GCPs should be evenly distributed over the entire uncorrected image.

Transformation Direction

Specifies the direction of the vector transformation.

If input and output units are both "PIXEL", however, the transformation could be made forward to the output "PIXEL" units or backward to the input "PIXEL" units. In such a case, the direction must be specified by this parameter.

Vector Layer Name

Specifies a name (up to 8 characters) for the output vector segment.

If this parameter is not specified, the DBSN value from the input vector segment is used.

Vector Layer Description

Describes (in up to 64 characters) the contents or origins of the output data.

If this parameter is not specified, the DBSD value from the input vector segment is used.

Details

VECREG performs registration of vector data on a vector segment using a ground control point (GCP) segment or a georeferencing segment, to produce a new segment of transformed vector data.

VECREG transforms (warps) vector data to fit a given set of ground control points or to map onto the area specified by the file's georeferencing segment. The specified input file (FILE) contains the segment of vector data to transform (DBVS) as well as the ground control point segment (DBGC) defining how the vector data is to be transformed.

The GCP segment is normally be produced by running the function GCIV, which will also output the required transform order. VECREG will produce a transformed vector segment that overlays the imagery, similarly to the transformed vectors displayed for the "Hi-Res" option during the tie-down process in GCIV. The segment number of the transformed vector data is output to the LASC parameter before VECREG exits. If a segment name (DBSN) and segment description (DBSD) are specified before running VECREG, they are used for the new vector segment; otherwise, the segment name and description from the input vector segment are used.

VECREG may also be used to translate and/or scale vector data as specified by the file's georeferencing segment. If the GCP segment (DBGC) input to VECREG is not specified, VECREG will transform the vectors using the affine transform defined by the georeferencing segment. The bounds for the georeferencing segment may be specified with GEOSET. If the georeferencing segment is to be used to make the transformation, the ORDER (Regression Order) parameter is ignored.

In most cases, the direction for the transformation can only go one way; that is, VECREG will transform the vectors from the coordinate system that matches the vector's coordinate system to the coordinate system that does not match. For example, if the vector units are "PIXEL" and the affine transform from the georeferencing segment (with input units of "PIXEL" and output units of "UTM") is to be used, the units for the output vectors will be "UTM". If the input and output units are both "PIXEL", however, the transformation could be made forward to the output "PIXEL" units or backward to the input "PIXEL" units. In such a case, the direction will be taken from the DIRECT (Transformation Direction) parameter specified for VECREG. If the direction for the transformation can only go one way, DIRECT is not necessary and is ignored. By default, DIRECT applies a FORWARD transformation.

VECREG can be used to warp vectors to overlay image data. This is done by producing a GCP segment using GCIV. The vectors are then transformed by VECREG to overlay the image, similar to the way vectors are displayed for the "Hi-res" option during the tie-down process with GCIV. This is done by applying a backward transformation to produce equivalent input coordinate "PIXEL" units.

VECREG can be used to transform vectors to another coordinate system (such as "PIXEL" to "UTM") by using the input file's georeferencing segment. That is, if the vectors are in the same "PIXEL" coordinate system as the image (for example, as produced by the backward transformation described earlier), and the bounds of the image are defined as "UTM" for the file's georeferencing segment with GEOSET, VECREG produces transformed UTM vectors.