Add some convenience geometry methods

CHANGELOG.md

@@ -9,6 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+* Added `compas.geometry.Line.point_from_start` and `compas.geometry.Line.point_from_end`.
+* Added `compas.geometry.Line.flip` and `compas.geometry.Line.flipped`.
 * Added an `compas.geometry.Frame.interpolate_frame(s)` method
 * Added `compas.colors.Color.contrast`.
 * Added `compas.geometry.Brep.from_plane`.

src/compas/geometry/curves/line.py

@@ -297,17 +297,19 @@ def transform(self, T):
     # ==========================================================================
 
     def point_at(self, t):
-        """Construct a point at a specific location along the line.
+        """Construct a point along the line at a fractional position.
 
         Parameters
         ----------
         t : float
-            The location along the line.
+            The relative position along the line as a fraction of the length of the line.
+            0.0 corresponds to the start point and 1.0 corresponds to the end point.
+            Numbers outside of this range are also valid and correspond to points beyond the start and end point.
 
         Returns
         -------
         :class:`compas.geometry.Point`
-            The point at the specified location.
+            The point at the specified position.
 
         See Also
         --------
@@ -323,6 +325,44 @@ def point_at(self, t):
         point = self.point + self.vector * t
         return point
 
+    def point_from_start(self, distance):
+        """Construct a point along the line at a distance from the start point.
+
+        Parameters
+        ----------
+        distance : float
+            The distance along the line from the start point towards the end point.
+            If the distance is negative, the point is constructed in the opposite direction of the end point.
+            If the distance is larger than the length of the line, the point is constructed beyond the end point.
+
+        Returns
+        -------
+        :class:`compas.geometry.Point`
+            The point at the specified distance.
+
+        """
+        point = self.point + self.direction * distance
+        return point
+
+    def point_from_end(self, distance):
+        """Construct a point along the line at a distance from the end point.
+
+        Parameters
+        ----------
+        distance : float
+            The distance along the line from the end point towards the start point.
+            If the distance is negative, the point is constructed in the opposite direction of the start point.
+            If the distance is larger than the length of the line, the point is constructed beyond the start point.
+
+        Returns
+        -------
+        :class:`compas.geometry.Point`
+            The point at the specified distance.
+
+        """
+        point = self.end - self.direction * distance
+        return point
+
     def closest_point(self, point, return_parameter=False):
         """Compute the closest point on the line to a given point.
 
@@ -349,3 +389,43 @@ def closest_point(self, point, return_parameter=False):
         if return_parameter:
             return closest, t
         return closest
+
+    def flip(self):
+        """Flip the direction of the line.
+
+        Returns
+        -------
+        None
+
+        Examples
+        --------
+        >>> line = Line([0, 0, 0], [1, 2, 3])
+        >>> line
+        Line(Point(x=0.0, y=0.0, z=0.0), Point(x=1.0, y=2.0, z=3.0))
+        >>> line.flip()
+        >>> line
+        Line(Point(x=1.0, y=2.0, z=3.0), Point(x=0.0, y=0.0, z=0.0))
+
+        """
+        new_vector = self.vector.inverted()
+        self.start = self.end
+        self.vector = new_vector
+
+    def flipped(self):
+        """Return a new line with the direction flipped.
+
+        Returns
+        -------
+        :class:`Line`
+            A new line.
+
+        Examples
+        --------
+        >>> line = Line([0, 0, 0], [1, 2, 3])
+        >>> line
+        Line(Point(x=0.0, y=0.0, z=0.0), Point(x=1.0, y=2.0, z=3.0))
+        >>> line.flipped()
+        Line(Point(x=1.0, y=2.0, z=3.0), Point(x=0.0, y=0.0, z=0.0))
+
+        """
+        return Line(self.end, self.start)

tests/compas/geometry/test_curves_line.py

@@ -11,6 +11,7 @@
 from compas.geometry import Vector
 from compas.geometry import Frame
 from compas.geometry import Line
+from compas.tolerance import TOL
 
 
 @pytest.mark.parametrize(
@@ -216,3 +217,68 @@ def test_line_accessors(p1, p2):
 # =============================================================================
 # Other Methods
 # =============================================================================
+
+
+@pytest.mark.parametrize(
+    "p1,p2",
+    [
+        ([0, 0, 0], [1, 0, 0]),
+        ([0, 0, 0], [1, 2, 3]),
+        ([1, 2, 3], [-1, -2, -3]),
+        ([-11.1, 22.2, 33.3], [1.1, -2.2, -3.3]),
+    ],
+)
+def test_line_point_from_start(p1, p2):
+    distances = [0, 1, 4, -9, 3.3, 0.00001, -0.00001]
+    for distance in distances:
+        line = Line(p1, p2)
+        point = line.point_from_start(distance)
+        distance_to_start = distance_point_point(point, p1)
+        distance_to_end = distance_point_point(point, p2)
+        # Check that the distance is correct
+        assert TOL.is_close(distance_to_start, abs(distance))
+        # Check that negative distance gives a point far away from end
+        if distance < 0:
+            assert distance_to_end > line.length
+
+
+@pytest.mark.parametrize(
+    "p1,p2",
+    [
+        ([0, 0, 0], [1, 0, 0]),
+        ([0, 0, 0], [1, 2, 3]),
+        ([1, 2, 3], [-1, -2, -3]),
+        ([-11.1, 22.2, 33.3], [1.1, -2.2, -3.3]),
+    ],
+)
+def test_line_point_from_end(p1, p2):
+    distances = [0, 1, 4, -9, 3.3, 0.00001, -0.00001]
+    for distance in distances:
+        line = Line(p1, p2)
+        point = line.point_from_end(distance)
+        distance_to_start = distance_point_point(point, p1)
+        distance_to_end = distance_point_point(point, p2)
+        # Check that the distance is correct
+        assert TOL.is_close(distance_to_end, abs(distance))
+        # Check that negative distance gives a point far away from start
+        if distance < 0:
+            assert distance_to_start > line.length
+
+
+@pytest.mark.parametrize(
+    "p1,p2",
+    [
+        ([0, 0, 0], [1, 0, 0]),
+        ([0, 0, 0], [1, 2, 3]),
+        ([1, 2, 3], [-1, -2, -3]),
+        ([-11.1, 22.2, 33.3], [1.1, -2.2, -3.3]),
+    ],
+)
+def test_line_flip(p1, p2):
+    line = Line(p1, p2)
+    line.flip()
+    assert TOL.is_zero(distance_point_point(line.start, p2))
+    assert TOL.is_zero(distance_point_point(line.end, p1))
+    flipped_line = Line(p1, p2).flipped()
+    assert TOL.is_zero(distance_point_point(flipped_line.start, p2))
+    assert TOL.is_zero(distance_point_point(flipped_line.end, p1))