fix: make sure that AFM metadata contain the spring constant

CHANGELOG

@@ -1,4 +1,6 @@
 3.1.3
+ - fix: make sure that AFM metadata contain the spring constant and
+   raise a MissingMetaDataError if this is not the case
  - ref: deprecate `IndentationPreprocessor` class in favor of a more
    flat submodule (#17)
 3.1.2

nanite/group.py

@@ -1,6 +1,7 @@
 import pathlib
 
 import afmformats
+from afmformats.errors import MissingMetaDataError
 
 from .read import get_load_data_modality_kwargs, load_data
 
@@ -59,3 +60,22 @@ def __init__(self, path=None, meta_override=None, callback=None):
             callback=callback,
             **get_load_data_modality_kwargs()
         )
+
+    def append(self, afmdata):
+        """Append a new instance of AFMData
+
+        This subclassed method makes sure that "spring constant" is set
+        if "tip position" has to be computed in the future.
+
+        Parameters
+        ----------
+        afmdata: afmformats.afm_data.AFMData
+            AFM data
+        """
+        if ("spring constant" not in afmdata.metadata
+                and "tip position" not in afmdata):
+            raise MissingMetaDataError(
+                ["spring constant"],
+                "Please specify the spring constant!")
+        # Call the original function
+        super(IndentationGroup, self).append(afmdata)