Update curve derivatives API

introduce explicit tangent_delta parameter.

Add "tangent_delta" to "curve curvature" node.

refs #3804

nodes/curve/curvature.py

@@ -6,6 +6,7 @@
 
 from sverchok.node_tree import SverchCustomTreeNode
 from sverchok.data_structure import updateNode, zip_long_repeat
+from sverchok.utils.curve.core import DEFAULT_TANGENT_DELTA
 
 class SvCurveCurvatureNode(bpy.types.Node, SverchCustomTreeNode):
         """
@@ -21,6 +22,17 @@ class SvCurveCurvatureNode(bpy.types.Node, SverchCustomTreeNode):
                 default = 0.5,
                 update = updateNode)
 
+        tangent_delta : FloatProperty(
+                name = "Tangent step",
+                description = "Derivatives calculation step; bigger values lead to more smooth results",
+                min = 0.0,
+                precision = 8,
+                default = DEFAULT_TANGENT_DELTA,
+                update = updateNode)
+
+        def draw_buttons_ext(self, context, layout):
+            layout.prop(self, 'tangent_delta')
+
         def sv_init(self, context):
             self.inputs.new('SvCurveSocket', "Curve")
             self.inputs.new('SvStringsSocket', "T").prop_name = 't_value'

utils/curve/bezier.py

@@ -235,31 +235,31 @@ def evaluate_array(self, ts):
         coeffs = np.array(coeffs)
         return np.dot(coeffs.T, self.points)
 
-    def tangent(self, t):
-        return self.tangent_array(np.array([t]))[0]
+    def tangent(self, t, tangent_delta=None):
+        return self.tangent_array(np.array([t]), tangent_delta=tangent_delta)[0]
 
-    def tangent_array(self, ts):
+    def tangent_array(self, ts, tangent_delta=None):
         coeffs = [self.coeff_deriv1(k, ts) for k in range(len(self.points))]
         coeffs = np.array(coeffs)
         #print("C1", coeffs)
         return np.dot(coeffs.T, self.points)
 
-    def second_derivative(self, t):
+    def second_derivative(self, t, tangent_delta=None):
         return self.second_derivative_array(np.array([t]))[0]
 
-    def second_derivative_array(self, ts):
+    def second_derivative_array(self, ts, tangent_delta=None):
         coeffs = [self.coeff_deriv2(k, ts) for k in range(len(self.points))]
         coeffs = np.array(coeffs)
         #print("C2", coeffs)
         return np.dot(coeffs.T, self.points)
 
-    def third_derivative_array(self, ts):
+    def third_derivative_array(self, ts, tangent_delta=None):
         coeffs = [self.coeff_deriv3(k, ts) for k in range(len(self.points))]
         coeffs = np.array(coeffs)
         #print("C3", coeffs)
         return np.dot(coeffs.T, self.points)
 
-    def derivatives_array(self, n, ts):
+    def derivatives_array(self, n, ts, tangent_delta=None):
         result = []
         if n >= 1:
             first = self.tangent_array(ts)