Data Smoothing: Thin-Plate Spline

Method Tab

You can use the Method tab to specify options for the thin-plate spline algorithm. (See Figure 19.5.) The Method tab contains the following UI controls:

Selection method

specifies how to choose the smoothing penalty parameter. This option corresponds to the SELECT= option in the MODEL statement.

GCV: selects the smoothing parameter that minimizes the generalized cross validation criterion.
Approx. model DF: selects the smoothing parameter for which the trace of the prediction matrix is closest to the Target model DF. This corresponds to SELECT=DF option.
Manual: enables you to specify the value in the log(n*lambda) field. This corresponds to the LOGNLAMBDA= option.

Maximum number of unique design points

specifies a limit on the number of unique design points, $N_ x$ , in the model. This option corresponds to the DISTANCE= option in the MODEL statement in the following way: the value in this field is used to compute a value for the DISTANCE= option so that there are at most $N_ x$ design points. This option is useful for large data sets, since the TPSPLINE procedure is computationally expensive.

Figure 19.5: The Method Tab