DOC: Mesh and Transform NumPy conversion

PointSet to be added to the documentation following the release of
InsightSoftwareConsortium/ITK#3799.

Author: thewtex

docs/Quick_start_guide.rst

@@ -27,16 +27,25 @@ ITK and NumPy
 
 A common use case for using ITK in Python is to mingle NumPy and ITK operations on raster data. ITK provides a large number of I/O image formats and several sophisticated image processing algorithms not available in any other packages. The ability to intersperse that with the SciPy ecosystem provides a great tool for rapid prototyping.
 
-The following script shows how to integrate NumPy and ITK:
+The following script shows how to integrate NumPy and `itk.Image`:
 
 .. literalinclude:: code/MixingITKAndNumPy.py
-   :lines: 8-33
+   :lines: 16-50
 
+NumPy and `itk.Mesh`:
 
-Similar functions are available to work with `itk.Matrix`, VNL vectors and matrices:
+.. literalinclude:: code/MixingITKAndNumPy.py
+   :lines: 53-67
+
+NumPy and `itk.Transform`:
+
+.. literalinclude:: code/MixingITKAndNumPy.py
+   :lines: 87-106
+
+NumPy and `itk.Matrix`, VNL vectors, and VNL matrices:
 
 .. literalinclude:: code/MixingITKAndNumPy.py
-   :lines: 35-
+   :lines: 109-
 
 ITK and Xarray
 ..............

docs/code/MixingITKAndNumPy.py

@@ -1,15 +1,23 @@
 #!/usr/bin/env python3
 
 import sys
+from pathlib import Path
 
-input_filename = sys.argv[1]
-output_filename = sys.argv[2]
+data_dir = Path(__file__).parent.resolve() / '..' / 'data'
+
+input_image_filename = sys.argv[1]
+temp_dir = Path(input_image_filename).parent
+output_image_filename = sys.argv[2]
+input_mesh_filename = data_dir / 'cow.vtk'
+output_mesh_filename = temp_dir / 'cow.vtk'
+input_transform_filename = data_dir / 'rigid.tfm'
+output_transform_filename = temp_dir / 'rigid.tfm'
 
 import itk
 import numpy as np
 
 # Read input image
-itk_image = itk.imread(input_filename)
+itk_image = itk.imread(input_image_filename)
 
 # Run filters on itk.Image
 
@@ -21,8 +29,12 @@
 # Equivalent
 np_copy = np.asarray(itk_image)
 
+# Pixel array and image metadata
+# in standard Python data types + NumPy array
+image_dict = itk.dict_from_image(itk_image)
+
 
-# Do NumPy stuff...
+# Do interesting things...
 
 
 # Convert back to ITK, view only, data is not copied
@@ -32,7 +44,67 @@
 itk_np_copy = itk.image_from_array(np_copy)
 
 # Save result
-itk.imwrite(itk_np_view, output_filename)
+itk.imwrite(itk_np_view, output_image_filename)
+
+# Convert back to itk image data structure
+itk_image = itk.image_from_dict(image_dict)
+
+
+# Read input mesh
+itk_mesh = itk.meshread(input_mesh_filename)
+
+# Convert to standard Python data types + NumPy arrays
+mesh_dict = itk.dict_from_mesh(itk_mesh)
+
+
+# Do interesting things...
+
+
+# Convert back to itk mesh data structure
+itk_mesh = itk.mesh_from_dict(mesh_dict)
+
+# Save result
+itk.meshwrite(itk_mesh, output_mesh_filename)
+
+
+# itk.Mesh inherits from itk.PointSet,
+# create a PointSet from the Mesh
+itk_pointset = itk.PointSet[itk.F, 3].New()
+itk_pointset.SetPoints(itk_mesh.GetPoints())
+itk_pointset.SetPointData(itk_mesh.GetPointData())
+
+# Convert to standard Python data types + NumPy arrays
+pointset_dict = itk.pointset_from_dict(itk_pointset)
+
+
+# Do interesting things...
+
+
+# Convert back to itk pointset instance
+itk_pointset = itk.pointset_from_dict(pointset_dict)
+
+
+# Read input transforms
+#
+# This is a Python list
+#
+# When there is more than one transformation
+# the list defines a transformation chain
+itk_transforms = itk.transformread(input_transform_filename)
+
+# Convert to standard Python data types + NumPy arrays
+transform_dicts = [itk.dict_from_transform(t) for t in itk_transforms]
+
+
+# Do interesting things...
+
+
+# Convert back to itk transform instance
+itk_transforms = [itk.transform_from_dict(t) for t in transform_dicts]
+
+# Save result
+itk.transformwrite(itk_transforms, output_transform_filename)
+
 
 # VNL matrix from np.ndarray
 arr = np.zeros([3,3], np.uint8)
@@ -53,3 +125,5 @@
 
 # np.ndarray from itk.Matrix
 arr = itk.array_from_matrix(mat)
+# Equivalent
+arr = np.asarray(mat)

docs/code/test.py

@@ -4,6 +4,7 @@
 import sys
 import os
 import tempfile
+import shutil
 
 def add_test(cmd):
     cmd.insert(0, sys.executable)
@@ -12,7 +13,7 @@ def add_test(cmd):
 def cleanup(files):
     for f in files:
         if os.path.isdir(f):
-            os.rmdir(f)
+            shutil.rmtree(f)
         else:
             os.remove(f)