Add new filter sample_over_line and refactor plot_over_line (pyvista#525

)

* Refactor plot over line to enable retrieving result

* Return line object instead

* Move positive resolution check to Line, remove integer check.  Add more testing.

* Remove extra blank line

* add missing blank line

pyvista/core/filters.py

@@ -1599,12 +1599,41 @@ def decimate_boundary(dataset, target_reduction=0.5):
         return dataset.extract_geometry().triangulate().decimate(target_reduction)
 
 
+    def sample_over_line(dataset, pointa, pointb, resolution=None):
+        """Sample a dataset onto a line.
+
+        Parameters
+        ----------
+        pointa : np.ndarray or list
+            Location in [x, y, z].
+
+        pointb : np.ndarray or list
+            Location in [x, y, z].
+
+        resolution : int
+            Number of pieces to divide line into. Defaults to number of cells
+            in the input mesh. Must be a positive integer.
+
+        Return
+        ------
+        sampled_line : pv.PolyData
+            Line object with sampled data from dataset.
+        """
+        if resolution is None:
+            resolution = int(dataset.n_cells)
+        # Make a line and sample the dataset
+        line = pyvista.Line(pointa, pointb, resolution=resolution)
+
+        sampled_line = line.sample(dataset)
+        return sampled_line
+
+
     def plot_over_line(dataset, pointa, pointb, resolution=None, scalars=None,
                        title=None, ylabel=None, figsize=None, figure=True,
                        show=True):
-        """Sample a dataset along a high resolution line.
+        """Sample a dataset along a high resolution line and plot.
 
-        Also plot the variables of interest in 2D where the X-axis is distance from
+        Plot the variables of interest in 2D where the X-axis is distance from
         Point A and the Y-axis is the variable of interest. Note that this filter
         returns None.
 
@@ -1646,21 +1675,16 @@ def plot_over_line(dataset, pointa, pointb, resolution=None, scalars=None,
         except ImportError:
             raise ImportError('matplotlib must be available to use this filter.')
 
-        if resolution is None:
-            resolution = int(dataset.n_cells)
-        if not isinstance(resolution, int) or resolution < 0:
-            raise RuntimeError('`resolution` must be a positive integer, not {}'.format(type(resolution)))
-        # Make a line and probe the dataset
-        line = pyvista.Line(pointa, pointb, resolution=resolution)
-        sampled = line.sample(dataset)
+        # Sample on line
+        sampled = DataSetFilters.sample_over_line(dataset, pointa, pointb, resolution)
 
         # Get variable of interest
         if scalars is None:
             field, scalars = dataset.active_scalars_info
         values = sampled.get_array(scalars)
         distance = sampled['Distance']
 
-        # Remainder of the is plotting
+        # Remainder is plotting
         if figure:
             plt.figure(figsize=figsize)
         # Plot it in 2D

pyvista/utilities/geometric_objects.py

@@ -338,6 +338,8 @@ def Line(pointa=(-0.5, 0., 0.), pointb=(0.5, 0., 0.), resolution=1):
         number of pieces to divide line into
 
     """
+    if resolution <= 0:
+        raise ValueError('Resolution must be positive')
     if np.array(pointa).size != 3:
         raise TypeError('Point A must be a length three tuple of floats.')
     if np.array(pointb).size != 3:

tests/test_filters.py

@@ -484,6 +484,27 @@ def test_streamlines():
     assert src.n_points == 25
 
 
+def test_sample_over_line():
+    """Test that we get a sampled line."""
+    name = 'values'
+
+    line = pyvista.Line([0, 0, 0], [0, 0, 10], 9)
+    line[name] = np.linspace(0, 10, 10)
+
+    sampled_line = line.sample_over_line([0, 0, 0.5], [0, 0, 1.5], 2)
+
+    expected_result = np.array([0.5, 1, 1.5])
+    assert np.allclose(sampled_line[name], expected_result)
+    assert name in line.array_names # is name in sampled result
+
+    # test no resolution
+    sphere = pyvista.Sphere(center=(4.5,4.5,4.5), radius=4.5)
+    sampled_from_sphere = sphere.sample_over_line([3, 1, 1], [-3, -1, -1])
+    assert sampled_from_sphere.n_points == sphere.n_cells + 1
+    # is sampled result a polydata object
+    assert isinstance(sampled_from_sphere, pyvista.PolyData)
+
+
 def test_plot_over_line():
     """this requires matplotlib"""
     mesh = examples.load_uniform()

tests/test_geometric_objects.py

@@ -1,4 +1,5 @@
 import numpy as np
+import pytest
 
 import pyvista
 
@@ -33,13 +34,22 @@ def test_plane():
 
 
 def test_line():
-    line = pyvista.Line((0,0,0), (10, 1., 3))
+    pointa = (0, 0, 0)
+    pointb = (10, 1., 3)
+
+    line = pyvista.Line(pointa, pointb)
     assert line.n_points == 2
     assert line.n_cells == 1
-    line = pyvista.Line((0,0,0), (10, 1., 3), 10)
+    line = pyvista.Line(pointa, pointb, 10)
     assert line.n_points == 11
     assert line.n_cells == 1
 
+    with pytest.raises(ValueError):
+        pyvista.Line(pointa, pointb, -1)
+
+    with pytest.raises(TypeError):
+        pyvista.Line(pointa, pointb, 0.1) # from vtk
+
 
 def test_cube():
     cube = pyvista.Cube()