Sphericity

Create a method to compute sphericity using a mesh based approach

qim3d/processing/features.py

 import numpy as np
+import qim3d.processing
 from qim3d.utils.logger import log
 import trimesh
 import qim3d
 
+
 def volume(obj, **mesh_kwargs) -> float:
     """
     Compute the volume of a 3D volume or mesh.
@@ -44,7 +46,8 @@ def volume(obj, **mesh_kwargs) -> float:
         log.info("Converting volume to mesh.")
         obj = qim3d.processing.create_mesh(obj, **mesh_kwargs)
 
-    return obj.volume
+    return abs(obj.volume)
+
 
 def area(obj, **mesh_kwargs) -> float:
     """
@@ -88,13 +91,14 @@ def area(obj, **mesh_kwargs) -> float:
 
     return obj.area
 
+
 def sphericity(obj, **mesh_kwargs) -> float:
     """
     Compute the sphericity of a 3D volume or mesh.
 
-    Sphericity is a measure of how spherical an object is. It is defined as the ratio 
-    of the surface area of a sphere with the same volume as the object to the object's 
-    actual surface area. 
+    Sphericity is a measure of how spherical an object is. It is defined as the ratio
+    of the surface area of a sphere with the same volume as the object to the object's
+    actual surface area.
 
     Args:
         obj: Either a np.ndarray volume or a mesh object of type trimesh.Trimesh.
@@ -127,7 +131,7 @@ def sphericity(obj, **mesh_kwargs) -> float:
         ```
 
     !!! info "Limitations Due to Pixelation"
-        Sphericity is particularly sensitive to the resolution of the mesh, as it directly impacts the accuracy of surface area and volume calculations. 
+        Sphericity is particularly sensitive to the resolution of the mesh, as it directly impacts the accuracy of surface area and volume calculations.
         Indeed, since the mesh is generated from voxel-based 3D volume data, the discrete nature of the voxels leads to pixelation effects that reduce the precision of sphericity measurements.
         Higher resolution meshes may mitigate these errors but often at the cost of increased computational demands.
     """
@@ -135,13 +139,13 @@ def sphericity(obj, **mesh_kwargs) -> float:
         log.info("Converting volume to mesh.")
         obj = qim3d.processing.create_mesh(obj, **mesh_kwargs)
 
-    V = volume(obj)
-    A = area(obj)
+    volume = qim3d.processing.volume(obj)
+    area = qim3d.processing.area(obj)
 
-    if A == 0:
+    if area == 0:
         log.warning("Surface area is zero, sphericity is undefined.")
         return np.nan
 
-    sphericity = (np.pi**(1/3) * (6 * V)**(2/3)) / A
+    sphericity = (np.pi ** (1 / 3) * (6 * volume) ** (2 / 3)) / area
     log.info(f"Sphericity: {sphericity}")
     return sphericity