Add docstring for signed distance function's trimesh2sdf (#211)

* Add docstring for signed distance function utilities

* [docs] Add document for sdf

* Enable padding_grid

* Raise ValueError for converting sdf

docs/source/reference/sdfs.rst

@@ -2,7 +2,7 @@ Signed distance function (SDF)
 ==============================
 
 SDF classes
--------------------
+-----------
 .. autosummary::
    :toctree: generated/
    :nosignatures:
@@ -11,3 +11,15 @@ SDF classes
    skrobot.sdf.UnionSDF
    skrobot.sdf.BoxSDF
    skrobot.sdf.GridSDF
+   skrobot.sdf.CylinderSDF
+   skrobot.sdf.SphereSDF
+
+SDF utilities
+-------------
+
+.. autosummary::
+   :toctree: generated/
+   :nosignatures:
+
+   skrobot.sdf.signed_distance_function.trimesh2sdf
+   skrobot.sdf.signed_distance_function.link2sdf

skrobot/sdf/signed_distance_function.py

@@ -17,11 +17,33 @@
 logger = getLogger(__name__)
 
 
-def trimesh2sdf(mesh, dim_grid):
+def trimesh2sdf(mesh, dim_grid=100, padding_grid=5):
+    """Convert trimesh to signed distance function.
+
+    Parameters
+    ----------
+    mesh : trimesh.base.Trimesh
+        mesh object.
+    dim_grid : int
+        dimension of the GridSDF.
+        This value is used for a not primitive mesh.
+    padding_grid : int
+        number of padding.
+
+    Returns
+    -------
+    sdf : skrobot.sdf.SignedDistanceFunction
+        converted signed distance function.
+    """
+    if not ('file_path' in mesh.metadata
+            or 'shape' in mesh.metadata):
+        raise ValueError("Input mesh doesn't contain valid metadata"
+                         " for converting SDF.")
     is_loaded_mesh = 'file_path' in mesh.metadata
     if is_loaded_mesh:
         file_path = mesh.metadata['file_path']
-        sdf = GridSDF.from_objfile(file_path, dim_grid=dim_grid)
+        sdf = GridSDF.from_objfile(file_path, dim_grid=dim_grid,
+                                   padding_grid=padding_grid)
     else:
         # process primtives
         shape = mesh.metadata['shape']