TPSMODEL

Description

TPSMODEL is a simple math model in which all the collected ground control points (GCPs) are used simultaneously to perform a transformation.

Parameters

Name	Type	Length	Value range
Input: Image Layers: Input image layers to be processed *	Raster port	1 - 1024
Input: GCP: Input Ground Control Point segment or layer	GCP port	0 - 1
OutputMM: Output math model segment or layer	BIN port	0 - 1
Report	String	0 - 192	See parameter description

* Required parameter

Parameter descriptions

Input: Image Layers: Input image layers to be processed

Specifies the input raw image layers to be processed.

Input: GCP: Input Ground Control Point segment or layer

Specifies the input GCP segment or layer to use when computing the model.

OutputMM: Output math model segment or layer

Specifies the output math model segment or layer in which to store the computed model.

Report

Specifies where to direct the generated report.

Available options are:

• LOG: generates a report on the terminal (default)
• <modulename.RPT>: appends a report to the module's RPT file
• DISK: generates a report on file "IMPRPT.LST"

Details

The Thin Plate Spline (TPS) is a simple math model in which all collected GCPs are used simultaneously to compute a transformation. Warping is distributed throughout the image with minimum curvature between the GCPs, becoming almost linear in areas away from the GCPs.

The TPS math model fits the GCPs exactly; therefore, a GCP can be added in an area where the transformation is not satisfactory. This also means, however, that the math model does not provide a direct means of detecting and correcting errors in GCP coordinates. To verify the derived transformations, you must acquire a number of check points that are large enough to ensure a thorough verification, such as an amount equal to half the number of GCPs.

The TPS math model can handle more variations in terrain than the polynomial math model, because it recognizes three-dimensional GCPs and minimizes the extrapolation errors that can occur between the GCPs.

To accurately compute a warping transformation, you must collect GCPs at the extremes of the terrain and along the breaklines. If you use the TPS math model with an image in rough terrain, it may be necessary to acquire hundreds of GCPs. For this reason, the TPS math model is recommended only for distortions that can be accurately represented using up to a few dozen GCPs. It is not recommended that you remove terrain distortions or images of rough terrain. For these types of images, a rigorous model, such as the satellite orbital or aerial photography math model, is recommended.