GP fit of astrometric residuals for a single 300 s z-band exposure. The fit is done independently for each component of the vector field. The top six plots show results for the du component and the bottom six plots for the dv component. The plots in the top row within each group illustrate how the hyperparameters are determined from a von Kármán kernel (center plot) fit to the measured two-point correlation function calculated for 80% of the training sample (left plot); the difference between the measured two-point correlation function and the best-fit von Kármán kernel is shown in the right-most plots. The plots in the bottom row within each group of six represent the variation across the focal plane of the measured component of the astrometric residual field, the astrometric residual field predicted by the GP using the best-fit hyperparameters, and the difference between measure and fit, projected in the local tangent plane for the 20% of sources in the validation sample.