diff -r e1ced2523cad -r b6cbba6e29a1 src/documentmanager.cpp
--- a/src/documentmanager.cpp	Tue Nov 02 15:43:57 2021 +0200
+++ b/src/documentmanager.cpp	Thu Mar 03 11:42:52 2022 +0200
@@ -45,8 +45,10 @@
 	const QString name = makeNewModelName();
 	this->openModels[modelId] = ModelInfo{
 		.model = std::make_unique<Model>(),
+		.id = modelId,
 		.opentype = OpenType::ManuallyOpened,
 	};
+	this->makePolygonCacheForModel(modelId);
 	return modelId;
 }
 
@@ -141,7 +143,8 @@
 	if (file.error() == QFile::NoError)
 	{
 		const ModelId modelId{++this->modelIdCounter};
-		this->openModels[modelId] = {std::move(newModel), path, openType};
+		this->openModels[modelId] = {std::move(newModel), modelId, path, openType};
+		this->makePolygonCacheForModel(modelId);
 		result = modelId;
 	}
 	else
@@ -299,6 +302,19 @@
 	return result;
 }
 
+PolygonCache *DocumentManager::getPolygonCacheForModel(ModelId modelId)
+{
+	auto it = this->polygonCaches.find(modelId);
+	if (it != this->polygonCaches.end())
+	{
+		return &it->second;
+	}
+	else
+	{
+		return nullptr;
+	}
+}
+
 /**
  * @brief Cleans up and erases models that are no longer required.
  */
@@ -311,6 +327,12 @@
 			and it->second.opentype == OpenType::AutomaticallyOpened
 			and not this->isReferencedByAnything(it->first)
 		) {
+			// Remove its polygon cache
+			const auto polygonCache = this->polygonCaches.find(it->first);
+			if (polygonCache != this->polygonCaches.end())
+			{
+				this->polygonCaches.erase(polygonCache);
+			}
 			// Remove the model
 			this->openModels.erase(it);
 			// We need to start over now. It is possible that other models that previously
@@ -345,6 +367,18 @@
 	return false;
 }
 
+void DocumentManager::makePolygonCacheForModel(const ModelId modelId)
+{
+	Model* model = this->getModelById(modelId);
+	if (model != nullptr)
+	{
+		this->polygonCaches.emplace(
+			std::piecewise_construct,
+			std::forward_as_tuple(modelId),
+			std::forward_as_tuple(model));
+	}
+}
+
 static QString findFile(QString referenceName, const QString& path, const LibraryManager& libraries)
 {
 	// Try to find the file in the same place as the model itself