在R-Caret中的指定网格上可视化指标

Question

为SVM运行火车功能并指定网格时：

ctrl <- trainControl(method = "repeatedcv", number = 10, repeats = 50, verboseIter = TRUE,
                       savePredictions = TRUE, classProbs = TRUE, summaryFunction = MySummary)
  SVMgrid <- expand.grid(sigma = seq(0.0025,0.03,0.0025), C = seq(0.5,20,2))
  mod_fit <- train(Thrombosis ~ .,  data=df, method="svmRadial", trControl=ctrl,
                   tuneGrid=SVMgrid, preProc=c("scale","YeoJohnson"), metric="Kappa",
                   allowParallel = TRUE)

输出是一个对象，该对象在指定的网格上具有所需指标的值：

> res$model$results
    sigma    C  Accuracy     Kappa
    1   0.0025  0.5 0.9133391 0.1749249
    2   0.0025  2.5 0.9138762 0.2059130
    3   0.0025  4.5 0.9183870 0.2710625
    4   0.0025  6.5 0.9194742 0.2730091
    5   0.0025  8.5 0.9198104 0.2733598
    6   0.0025 10.5 0.9204425 0.2787055
    7   0.0025 12.5 0.9210958 0.2811878
    8   0.0025 14.5 0.9217887 0.2869429
    9   0.0025 16.5 0.9224985 0.2897108
    10  0.0025 18.5 0.9222014 0.2837258
    11  0.0050  0.5 0.9154192 0.2231682

如何将其可视化为正方形网格或另一种合适的方式？