SumModel: sum models have a constant rescale factor of 1 since they a…

…re derived from correlation not cor

src/gstools/covmodel/base.py

@@ -1193,6 +1193,7 @@ class SumModel(CovModel):
     An empty sum represents a pure Nugget model.
     Resetting the total variance or the total length scale will evenly
     scale the variances or length scales of the sub models.
+    Sum models will have a constant rescale factor of one.
 
     Parameters
     ----------
@@ -1235,12 +1236,6 @@ class SumModel(CovModel):
         If given, ``len_scale`` will be ignored and recalculated,
         so that the integral scale of the model matches the given one.
         Default: :any:`None`
-    rescale : :class:`float` or :any:`None`, optional
-        Optional rescaling factor to divide the length scale with.
-        This could be used for unit conversion or rescaling the length scale
-        to coincide with e.g. the integral scale.
-        Will be set by each model individually.
-        Default: :any:`None`
     latlon : :class:`bool`, optional
         Whether the model is describing 2D fields on earths surface described
         by latitude and longitude. When using this, the model will internally
@@ -1364,7 +1359,6 @@ def __init__(self, *models, **kwargs):
         self._sft = None
         self.dim = kwargs.get("dim", self.models[0].dim if self.models else 3)
         # prepare parameters (they are checked in dim setting)
-        self._rescale = 1.0
         anis = kwargs.get("anis", self.models[0].anis if self.models else 1)
         angles = kwargs.get(
             "angles", self.models[0].angles if self.models else 0
@@ -1477,6 +1471,11 @@ def models(self):
         """:class:`tuple`: The summed models."""
         return self._models
 
+    @property
+    def rescale(self):
+        """:class:`float`: SumModel has a constant rescale factor of one."""
+        return 1.0
+
     @property
     def geo_scale(self):
         """:class:`float`: Geographic scaling for geographical coords."""