fix: adding analytical fold builder

Author: lachlangrose

LoopStructural/modelling/features/builders/__init__.py

@@ -3,3 +3,4 @@
 from ._folded_feature_builder import FoldedFeatureBuilder
 from ._structural_frame_builder import StructuralFrameBuilder
 from ._fault_builder import FaultBuilder
+from ._analytical_fold_builder import AnalyticalFoldBuilder

LoopStructural/modelling/features/builders/_analytical_fold_builder.py

@@ -0,0 +1,21 @@
+from ._base_builder import BaseBuilder
+from .._lambda_geological_feature import LambdaGeologicalFeature
+import numpy as np
+class AnalyticalFoldBuilder(BaseBuilder):
+    def __init__(self, model, name: str = 'Feature'):
+        super().__init__(model=model,name=name)
+        self._wavelength = np.max(model.bounding_box.length)
+        self._amplitude = np.min(model.bounding_box.length)
+        self._centre = model.bounding_box
+    @property
+    def amplitude(self):
+        return self._amplitude
+    @property
+    def wavelength(self):
+        return self._wavelength
+    
+    @property
+    def feature(self):
+        def function(xyz):
+            return xyz[:,2]+np.sin(xyz[:,0]/self.wavelength)*self.amplitude
+        return LambdaGeologicalFeature(function=function,model=self.model,name=self.name)