do not apply crosscorr to the bottom interface

GUI/Model/ToCore/SampleToCore.cpp

@@ -124,8 +124,9 @@ std::unique_ptr<MultiLayer> GUI::ToCore::itemToSample(const SampleItem& sampleIt
             roughItem->certainInterlayerModel()->createModel();
 
         std::unique_ptr<CrosscorrelationModel> crosscorrelation;
-        if (const auto* item = roughItem->certainCrosscorrModel())
-            crosscorrelation = item->createModel();
+        if (!layerItem->isBottomLayer())
+            if (const auto* item = roughItem->certainCrosscorrModel())
+                crosscorrelation = item->createModel();
 
         LayerRoughness roughness(autocorrelation.get(), interlayer.get(), crosscorrelation.get());
         sample->addLayerWithTopRoughness(*layer, roughness);